tag:theconversation.com,2011:/ca-fr/topics/corals-1254/articlesCorals – La Conversation2024-03-28T12:47:33Ztag:theconversation.com,2011:article/2244802024-03-28T12:47:33Z2024-03-28T12:47:33ZAs climate change and pollution imperil coral reefs, scientists are deep-freezing corals to repopulate future oceans<figure><img src="https://images.theconversation.com/files/584286/original/file-20240326-20-w2d62d.jpg?ixlib=rb-1.1.0&rect=29%2C0%2C3964%2C2994&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Healthy corals like these on Australia's Lady Elliot Reef could disappear by the 2030s if climate change is not curbed. </span> <span class="attribution"><span class="source">Rebecca Spindler</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Coral reefs are some of the <a href="https://sanctuaries.noaa.gov/education/teachers/coral-reef/background.html">oldest, most diverse ecosystems</a> on Earth, and among the most valuable. They nurture <a href="https://www.noaa.gov/education/resource-collections/marine-life/coral-reef-ecosystems">25% of all ocean life</a>, <a href="https://oceanservice.noaa.gov/facts/coral_protect.html">protect coasts from storms</a> and add <a href="https://oceanservice.noaa.gov/facts/coral_economy.html">billions of dollars yearly</a> to the global economy through their influences on fisheries, new pharmaceuticals, tourism and recreation. </p>
<p>Today, the world’s coral reefs are degrading at <a href="https://oceanservice.noaa.gov/education/tutorial_corals/coral09_humanthreats.html">unprecedented rates</a> due to pollution, overfishing and <a href="https://doi.org/10.1016/j.biocon.2017.04.024">destructive forestry</a> and <a href="https://doi.org/10.1016/j.scitotenv.2019.07.139">mining practices</a> on land. Climate change driven by human activities is <a href="https://www.ipcc.ch/report/ar6/wg1/downloads/factsheets/IPCC_AR6_WGI_Regional_Fact_Sheet_Ocean.pdf">warming and acidifying the ocean</a>, producing a <a href="https://theconversation.com/corals-are-starting-to-bleach-as-global-ocean-temperatures-hit-record-highs-209770">reef crisis</a> that could cause most corals to go extinct <a href="https://doi.org/10.1029/2021EF002608">within a few generations</a>. </p>
<p>I am a <a href="https://www.researchgate.net/scientific-contributions/Mary-Hagedorn-2111114778">marine biologist</a> at the Smithsonian’s <a href="https://nationalzoo.si.edu/conservation/about-scbi">National Zoo and Conservation Biology Institute</a>. For 17 years, I have worked with colleagues to create a global science program called the <a href="https://global.si.edu/projects/reef-recovery-initiative">Reef Recovery Initiative</a> that aims to help save coral reefs by using the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/cryopreservation">science of cryopreservation</a>. </p>
<p>This novel approach involves storing and cooling coral sperm and larvae, or <a href="https://wi.mit.edu/news/immortality-germ-cells">germ cells</a>, at very low temperatures and holding them in <a href="https://naturalhistorymuseum.blog/2022/07/26/biodiversity-biobanks-an-invaluable-resource-for-the-future/">government biorepositories</a>.</p>
<p>These repositories are an important hedge against extinction for corals. Managed effectively, they can help offset threats to the Earth’s reefs on a global scale. These frozen assets can be used today, 10 years or even 100 years from now to help reseed the oceans and restore living reefs.</p>
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<figcaption><span class="caption">Smithsonian scientists use cryopreserved coral sperm to increase the genetic diversity of elkhorn coral.</span></figcaption>
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<h2>Safely frozen alive</h2>
<p>Cryopreservation is a process for freezing biological material while maintaining its viability. It involves introducing sugarlike substances, called cryoprotectants, into cells to help prevent lethal ice formation during the freezing phase. If done properly, the cells remain frozen and alive in liquid nitrogen, unchanged, for many years. </p>
<p>Many organisms survive through cold winters in nature by becoming naturally cryopreserved as temperatures in their habitats drop below freezing, Two examples that are common across North America are <a href="https://new.nsf.gov/news/how-do-microscopic-creatures-called-tardigrades">tardigrades – microscopic animals that live in mosses and lichens</a> – and <a href="https://doi.org/10.1016/j.cbpb.2022.110747">wood frogs</a>. </p>
<p>Today, coral cryopreservation techniques rely largely on <a href="https://doi.org/10.1371/journal.pone.0033354">freezing sperm</a> <a href="https://doi.org/10.1038/s41598-018-34035-0">and larvae</a>. Since 2007, I have trained many colleagues in coral cryopreservation and worked with them to successfully preserve coral sperm. Today we have sperm from over 50 species of corals <a href="https://nationalzoo.si.edu/center-for-species-survival/coral-species-cryopreserved-global-collaborators">preserved in biorepositories worldwide</a>. </p>
<p>We have used this cryopreserved sperm to produce new coral across the Caribbean via a selective breeding process called <a href="https://doi.org/10.1073/pnas.2110559118">assisted gene flow</a>. The goal was to use cryopreserved sperm and interbreed corals that would not necessarily have encountered each other – a type of long-distance matchmaking. </p>
<p>Genetic diversity is maintained by combining as many different parents as possible to produce new sexually produced offspring. Since corals are cemented to the seabed, when population numbers in their area decline, new individuals can be introduced via cryopreservation. The hope is that these new genetic combinations might have an adaptation that will help coral survive changes in future warming oceans.</p>
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<a href="https://images.theconversation.com/files/584774/original/file-20240327-20-jmcyqb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two coral heads, one bleached white, the other still its natural brown color." src="https://images.theconversation.com/files/584774/original/file-20240327-20-jmcyqb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/584774/original/file-20240327-20-jmcyqb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/584774/original/file-20240327-20-jmcyqb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/584774/original/file-20240327-20-jmcyqb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/584774/original/file-20240327-20-jmcyqb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/584774/original/file-20240327-20-jmcyqb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/584774/original/file-20240327-20-jmcyqb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Corals in Kaneohe Bay, Hawaii during 2014 and 2015 warming events in which over 80% of corals were affected. Some species and individuals, like the coral at left, were resistant to warming.</span>
<span class="attribution"><span class="source">Claire Lager, Smithsonian</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>These assisted gene flow studies produced 600 new genetic-assorted individuals of the threatened elkhorn coral <em>Acropora palmata</em>. As of early 2024, there are only about 150 elkhorn individuals left in the wild in the Florida population. If given the chance, these selectively bred corals held in captivity could significantly increase the wild elkhorn gene pool. </p>
<p>Preserving sperm cells and larvae is an important hedge against the loss of biodiversity and species extinctions. But we can only collect this material during <a href="https://www.youtube.com/watch?v=eO_2JJynlOA">fleeting spawning events</a> when corals release egg and sperm into the water. </p>
<p>These episodes occur over just a few days a year – a small time window that poses logistical challenges for researchers and conservationists, and limits the speed at which we can successfully cryo-bank coral species. </p>
<p>To complicate matters further, warming oceans and increasingly frequent marine heat waves can biologically stress corals. This can make their reproductive material too weak to withstand the rigors of being cryopreserved and thawed. </p>
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<a href="https://images.theconversation.com/files/582584/original/file-20240318-24-kam7rc.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/582584/original/file-20240318-24-kam7rc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/582584/original/file-20240318-24-kam7rc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=482&fit=crop&dpr=1 600w, https://images.theconversation.com/files/582584/original/file-20240318-24-kam7rc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=482&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/582584/original/file-20240318-24-kam7rc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=482&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/582584/original/file-20240318-24-kam7rc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=605&fit=crop&dpr=1 754w, https://images.theconversation.com/files/582584/original/file-20240318-24-kam7rc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=605&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/582584/original/file-20240318-24-kam7rc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=605&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">An elkhorn coral produced through assisted gene flow, showing vigorous growth and development.</span>
<span class="attribution"><span class="source">Cody Engelsma</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<h2>Scaling up the rescue</h2>
<p>To collect coral material faster, we are developing a cryopreservation process for whole coral fragments, using a method called <a href="https://doi.org/10.1038/s41467-023-40500-w">isochoric vitrification</a>. This technique is still developing. However, if fully successful, it will preserve whole coral fragments without causing ice to form in their tissues, thus producing viable fragments after they’ve thawed that thrive and can be placed back out on the reef. </p>
<p>To do this, we dehydrate the fragment by exposing it to a viscous cryoprotectant cocktail. Then we place it into a small aluminum cylinder and immerse the cylinder in liquid nitrogen, which has a temperature of <a href="https://www.sciencedirect.com/topics/chemical-engineering/liquid-nitrogen">minus 320 degrees Fahrenheit (minus 196 Celsius)</a>. </p>
<p>This process freezes the cylinder’s contents so fast that the cryoprotectant forms a clear glass instead of allowing ice crystals to develop. When we want to thaw the fragments, we place them into a warm water bath for a few minutes, then rehydrate them in seawater. </p>
<p>Using this method, we can collect and cryopreserve coral fragments year-round, since we don’t have to wait and watch for fleeting spawning events. This approach greatly accelerates our conservation efforts. </p>
<p>Protecting as many species as possible will require expanding and sharing our science to create robust cryopreserved-and-thawed coral material through multiple methods. My colleagues and I want the technology to be easy, fast and cheap so any professional can replicate our process and help us preserve corals across the globe. </p>
<p>We have created a video-based coral cryo-training program that includes directions for <a href="https://nationalzoo.si.edu/center-for-species-survival/coral-cryopreservation-training-course">building simple, 3D-printed cryo-freezers</a>, and have collaborated with engineers to develop new methods that now allow coral larvae to be frozen by the hundreds on <a href="https://doi.org/10.1002/advs.202303317">simple, inexpensive metal meshes</a>. These new tools will make it possible for labs around the world to significantly accelerate coral collection around the globe within the next five years.</p>
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<figcaption><span class="caption">Without coral reefs, the world would lose a valuable source of food, coastal protection, medicines and income – and some of the world’s most unique and beautiful ecosystems.</span></figcaption>
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<h2>Safeguarding the future</h2>
<p>Recent climate models estimate that if greenhouse gas emissions continue unabated, 95% or more of the world’s corals <a href="https://doi.org/10.1371/journal.pclm.0000004">could die by the mid-2030s</a>. This leaves precious little time to conserve the biodiversity and genetic diversity of reefs.</p>
<p>One approach, which is already under way, is bringing all coral species into human care. The Smithsonian is part of the <a href="https://nationalzoo.si.edu/center-for-species-survival/coral-biobank-alliance">Coral Biobank Alliance</a>, an international collaboration to conserve corals by collecting live colonies, skeletons and genetic samples and using the best scientific practices to help rebuild reefs. </p>
<p>To date, over 200 coral species, out of some 1,000 known hard coral species, and thousands of colonies are under human care in institutions around the world, including organizations connected with the U.S. and European arms of the <a href="https://www.aza.org/">Association of Zoos and Aquariums</a>. Although these are clones of colonies from the wild, these individuals could be put into coral breeding systems that could be used for later cryopreservation of their genetically-assorted larvae. Alternatively, their larvae could be used for reef restoration projects. </p>
<p>Until climate change is slowed and reversed, reefs will continue to degrade. Ensuring a better future for coral reefs will require building up coral biorepositories, establishing on-land nurseries to hold coral colonies and develop new larval settlers, and training new cryo-professionals. </p>
<p>For decades, zoos have used <a href="https://www.cnn.com/2020/09/17/world/captive-breeding-species-cte-scn-spc-intl/index.html">captive breeding and reintroduction</a> to protect animals species that have fallen to critically low levels. Similarly, I believe our novel solutions can create hope and help save coral reefs to reseed our oceans today and long into the future.</p><img src="https://counter.theconversation.com/content/224480/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mary Hagedorn receives funding from Revive & Restore; Paul M. Angell Family Foundation; Volgenau Foundation; CORDAP Foundation; Zegar Family Foundation; Oceankind; Mastriani Family; De Witt Family; Anela Kolohe Foundation; Cedar Hill Foundation; Sidney E. Frank Foundation; Scintilla Foundation; and the Smithsonian Women’s Committee.
She is affiliated with Smithsonian National Zoo and Conservation Biology Institute and the Hawaii Institute of Marine Biology. </span></em></p>Just as the world’s zoos breed critically endangered animals in captivity to repopulate the wild, scientists are building a global effort to freeze corals for reef restoration.Mary Hagedorn, Research Scientist, Smithsonian InstitutionLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2253482024-03-09T08:43:31Z2024-03-09T08:43:31ZThe Great Barrier Reef’s latest bout of bleaching is the fifth in eight summers – the corals now have almost no reprieve<p>For the fifth time in just the past eight summers – 2016, 2017, 2020, 2022 and now 2024 - huge swathes of the Great Barrier Reef are experiencing extreme heat stress that has triggered yet another <a href="https://www2.gbrmpa.gov.au/learn/reef-health/reef-health-updates">episode of mass coral bleaching</a>. </p>
<p>Including two earlier heating episodes – in 1998 (which was at the time the hottest year globally on record) and 2002 – this brings the tally to seven such extreme events in the past 26 years. </p>
<p>The most conspicuous impact of unusually high temperatures on tropical and subtropical reefs is wide-scale coral bleaching and death. Sharp spikes in temperature can destroy coral tissue directly even before bleaching unfolds. Consequently, if temperatures exceed 2°C above the normal summer maximum, heat-sensitive corals die very quickly. </p>
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<figcaption><span class="caption">Reef Health Update (8 March 2024) Great Barrier Reef Marine Park Authority.</span></figcaption>
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<h2>What is coral bleaching?</h2>
<p>Bleaching happens when marine heatwaves disrupt the relationship between corals and their “photosynthetic symbionts” – tiny organisms that live inside the corals’ tissues and help power their metabolism.</p>
<p>Severe bleaching is often fatal, whereas corals that are mildly bleached can slowly regain their symbionts and normal colour after the end of summer, and survive. </p>
<p>Before 1998, coral bleaching on the Great Barrier Reef was infrequent and localised. But over the past four decades, bleaching has increased in frequency, severity and sptial scale, as a result of <a href="https://www.science.org/doi/10.1126/science.aan8048">human-induced climate heating</a>.</p>
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Read more:
<a href="https://theconversation.com/we-just-spent-two-weeks-surveying-the-great-barrier-reef-what-we-saw-was-an-utter-tragedy-135197">We just spent two weeks surveying the Great Barrier Reef. What we saw was an utter tragedy</a>
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<p>“Mass coral bleaching” refers to bleaching that is severe and widespread, affecting reefs at a regional scale or even throughout the tropics triggered by rising global sea temperatures.</p>
<p>The Great Barrier Reef consists of more than 3,000 individual coral reefs. It’s the same size as Japan or Italy, and extends for 2,300km along the coast of Queensland. Widespread coral deaths during extreme heatwaves, affecting hundreds of millions of coral colonies, <a href="https://onlinelibrary.wiley.com/doi/10.1111/gcb.15805">far exceed the damage</a> typically caused by a severe cyclone.</p>
<h2>How bad is 2024?</h2>
<p>Heat stress this week is reaching record levels on large parts of the Great Barrier Reef. </p>
<p>Climate scientists can measure the accumulation of heat stress throughout the summer by using a metric called “<a href="https://www.pacioos.hawaii.edu/voyager/info/coral_bleaching_degree_heating_week.html">degree heating weeks</a>” (DHW), which factors in both the duration and intensity of extreme heat exposure. This measures how far the temperature is above the threshold that triggers mild bleaching (1°C hotter than the normal summer maximum), and how long it stays above that threshold.</p>
<p>The same DHW exposure can result either from a long, moderate heatwave or from a short, intense peak in temperatures. The 2023–24 summer has been a slow burner on the Great Barrier Reef – sea temperatures have not been as extreme as during previous bleaching events, but they have <a href="http://www.bom.gov.au/oceanography/oceantemp/sst-outlook-map.shtml">persisted for longer</a>.</p>
<p>As a general rule of thumb, 2–4 DHW units can trigger the onset of bleaching, and heat-sensitive species of coral begin to die at 6–8 DHW units. So far this summer, <a href="https://x.com/profterryhughes/status/1762293105175445921?s=12&t=jfoU3j0RiQtYeeHqbSpjlA">according to the US National Oceanographic and Atmospheric Administration</a>, heat stress on the Great Barrier Reef has climbed to 10–12 DHW units on many individual reefs, and has been north and south compared to the central region. Heat stress will likely peak in the next week or two at levels above all previous mass bleaching and mortality events since 1998, before falling as temperatures drop.</p>
<p>Coral bleaching is typically very patchy at the enormous scale of the Great Barrier Reef. In each of the previous events since 1998, <a href="https://www.cell.com/current-biology/pdfExtended/S0960-9822(21)01490-1">20–55% of individual reefs</a> experienced severe bleaching and coral deaths, whereas 14–48% of reefs were unharmed.</p>
<p>Given the near-record levels of heat stress this summer, we can expect heavy losses of corals to occur on hundreds of individual reefs over the next few months.</p>
<h2>What’s the longer-term outlook?</h2>
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<p>This latest, still-unfolding event was entirely predictable, as ocean temperatures continue to rise due to global heating. </p>
<p>Three of the seven mass bleaching events so far on the Great Barrier Reef coincided with El Niño conditions (1998, 2016 and this summer), and the remaining four did not. Increasingly, climate-driven coral bleaching and death is happening regardless of whether we are in an El Niño or La Niña phase. Average tropical sea surface temperatures are <a href="https://www.science.org/doi/10.1126/science.aan8048">already warmer today</a> under La Niña conditions than they were during El Niño events only three or four decades ago.</p>
<p>The Great Barrier Reef is now a chequerboard of reefs with different recent histories of coral bleaching. Reefs that bleached in 2017 or 2016 have had only five or six years to recover before being hit again this summer – assuming they escaped bleaching during the 2020 and 2022 episodes. </p>
<p>Clearly, the gap between consecutive heat extremes is shrinking – we are vanishingly unlikely to see another 14-year reprieve like 2002 to 2016 again in our lifetimes, until global temperatures stabilise.</p>
<p>Ironically, the corals that are now prevalent on many reefs are young colonies of fast-growing, heat-sensitive species of branching and table-shaped corals – analogous to the rapid recovery of flammable grasses after a forest fire. These species can restore coral cover quickly, but they also make the Great Barrier Reef more vulnerable to future heatwaves. </p>
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Read more:
<a href="https://theconversation.com/concern-for-the-great-barrier-reef-can-inspire-climate-action-but-the-way-we-talk-about-it-matters-216992">Concern for the Great Barrier Reef can inspire climate action - but the way we talk about it matters</a>
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<p>Attempts to restore depleted coral cover through coral gardening, assisted migration (by harvesting larvae) and assisted evolution (rearing corals in an aquarium) are prohibitively expensive and <a href="https://www.cell.com/one-earth/pdf/S2590-3322(23)00189-6.pdf">unworkable at any meaningful scale</a>. In Florida, coral nurseries <a href="https://thehill.com/homenews/ap/ap-u-s-news/ap-hot-seawater-killed-most-of-cultivated-coral-in-florida-keys-in-setback-for-restoration-effort/">suffered mass deaths</a> due to record sea temperatures last summer.</p>
<p>The only long-term way to protect corals on the Great Barrier Reef and elsewhere is to rapidly reduce global greenhouse emissions.</p><img src="https://counter.theconversation.com/content/225348/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Terry Hughes does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The Great Barrier Reef is facing its worst summer of sustained heat stress since the mass bleaching event of 1998, but now with less time to recover amid repeated brutal conditions.Terry Hughes, Distinguished Professor, James Cook UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2211462024-01-25T14:45:02Z2024-01-25T14:45:02ZThe deep Mediterraneen: a temporary refuge for gorgonian coral forests facing marine heat waves<figure><img src="https://images.theconversation.com/files/569263/original/file-20231207-29-5ng5yh.jpg?ixlib=rb-1.1.0&rect=119%2C23%2C7821%2C5225&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">At a depth of more than 60 metres, the gorgonians are healthy, colourful and in good condition, protected from the rise in temperature.</span> <span class="attribution"><span class="source">Alexis Rosenfeld/Unesco</span>, <span class="license">Fourni par l'auteur</span></span></figcaption></figure><p>Over the last 20 years, the world’s oceans have experienced a significant increase in episodes of high-sea surface temperatures, known as <a href="https://theconversation.com/ocean-heat-is-off-the-charts-heres-what-that-means-for-humans-and-ecosystems-around-the-world-207902">marine heat waves</a>.</p>
<p>These events have become more frequent and intense over time, leading to significant changes in <a href="https://theconversation.com/el-nino-is-coming-and-ocean-temps-are-already-at-record-highs-that-can-spell-disaster-for-fish-and-corals-202424">marine ecosystems</a>. High ocean temperatures often lead to massive die-offs <a href="https://doi.org/10.1146/annurev-marine-032122-121437">among marine organisms</a>.</p>
<p>This phenomenon is particularly pronounced during the summer months in the Mediterranean Sea between July and August. Among the <a href="https://theconversation.com/inside-the-mediterranean-seas-animal-forests-an-encounter-with-the-gorgonian-corals-180194">species greatly affected by this environmental disturbance</a> is the red gorgonian, <em>Paramuricea clavata</em>.</p>
<p>Corals have a major ecological importance because of <a href="http://hdl.handle.net/10261/185600">their role as an engineer species</a>. When populations of red gorgonians reach high densities of large individuals, they create habitats similar to underwater forests that serve as a refuge or hunting ground for many species, thereby enhancing local biodiversity. Their decline can therefore have devastating consequences for the marine ecosystem as a whole.</p>
<p>However, <a href="https://ejournals.epublishing.ekt.gr/index.php/hcmr-med-mar-sc/article/view/35564">recent research carried out with several colleagues</a> suggests that by finding refuge deeper in the sea, where the temperature does not rise as much, red gorgonians could escape marine heat waves.</p>
<h2>Marine heat waves and mortality</h2>
<p>Episodes of mass mortality of red gorgonian have been reported since the 1980s, but the frequency of documented events <a href="https://doi.org/10.1371/journal.pone.0115655">intensified from 1999 onwards</a>: 2003, 2006, 2018 and 2022…</p>
<p>Just as fires devastate forests on land, marine heatwaves decimate shallow populations in the Mediterranean, from Spain to France and Italy, as well as in Croatia. The heatwave of summer 2022, one of the most dramatic in the history of the western Mediterranean, was particularly deadly for red gorgonian at depths of <a href="https://doi.org/10.1111/gcb.16931">up to 30 metres</a>.</p>
<p>The severity of these losses – directly linked to <a href="https://doi.org/10.1146/annurev-marine-032122-121437">heat at the sea surface</a> – seems to depend both on the severity of the temperature rise and the length of time that the high temperatures persist. Two parameters that together make its survival increasingly difficult.</p>
<h2>Looking for cooler water at greater depths</h2>
<p>Despite this worrying situation, there is still a glimmer of hope. The red gorgonian has a wide bathymetric range – in other words, the depth range within which the species can survive. If this range is wide, the species will be present both near the surface and at greater depths.</p>
<p>This is the case here, since it is found between 10 and 200 metres: even if the surface populations decline, those at greater depths remain. Conversely, a species found only in the first 30 metres of water would be completely eliminated by mortality linked to the rise in water temperature.</p>
<p>Up until now, readings indicate that during marine heat waves, the temperature decreases the deeper you go. In other words, gorgonian forests can still find refuge in deeper areas to protect themselves from the threats they face at the surface.</p>
<h2>Insufficient scientific data</h2>
<p>Unfortunately, most of the <a href="https://doi.org/10.3389/fmars.2019.00707">scientific data</a> on red gorgonian mortality mainly concern shallow populations, located at depths of between 15 and 25 metres, with a few rare cases going beyond 30 metres.</p>
<p>Recently, citizen science programmes – often carried out by recreational scuba divers – have played an essential role in the early detection of these mortality events by providing valuable data. But their observations are generally limited to shallow depths.</p>
<p>Thanks to significant advances in scuba diving technologies, scientists are now able to conduct research at unprecedented depths. The adoption of closed-circuit rebreathers (CCRs), which recycle exhaled air, allows for longer dives, and the use of breathing gas mixtures, known as TRIMIXs, make dives to even greater depths possible.</p>
<p>Thanks to these advances, our group of French (CNRS, Ifremer, Sorbonne and Septentrion Environnement) and Spanish (CSIC) researchers has been able to monitor the health of red gorgonian populations at depths of up to 90 metres in the Mediterranean Sea.</p>
<h2>Mortality down at depths of over 40 metres</h2>
<p>Analysis of data collected from 14 deep red gorgonian populations between 40 and 90 metres deep, combined with data from 29 shallower populations from a citizen science initiative (T-MedNet database), revealed a significant reduction in mortality below the <a href="https://doi.org/10.12681/mms.35564">40-metre threshold</a>.</p>
<p>This discovery suggests that the zone below 40 metres, also known as the mesophotic zone – or twilight zone due to the marked reduction in <a href="https://doi.org/10.1007/978-3-319-17001-5_4-1">light penetration</a> – may function as a refuge for the Mediterranean red gorgonian, protecting its populations from the harmful effects of marine heat waves.</p>
<p>These findings confirm the <a href="https://link.springer.com/article/10.1007/s00338-009-0581-x">“deep reef refugia” hypothesis</a>, according to which marine populations residing at greater depths are less sensitive to the impacts of climate change, particularly with regard to rising sea surface temperatures.</p>
<h2>Temporary refuge</h2>
<p>However, our knowledge of populations below 40 metres is still limited, which restricts our ability to predict how marine heat waves will affect them.</p>
<p>The preservation of populations at depth may not last when more frequent and severe marine heat waves affect temperatures at previously unexposed depths. At that point, populations in deeper areas could also have a lower heat tolerance <a href="https://doi.org/10.1016/j.jembe.2007.12.006">than their shallower counterparts</a> and therefore be more vulnerable.</p>
<p>As a result, this refuge at depth does not definitively protect gorgonians from the effects of climate change. Their survival will depend above all on the extent of connectivity between these populations (in other words, their ability to intermingle) and their reaction to rising water temperatures, parameters that are still poorly understood.</p>
<h2>Better understanding for better protection</h2>
<p>It is therefore vital to improve our knowledge of the mesophotic zone, the connectivity between deep and shallow populations and the way in which each population adapts to changing environmental conditions, in order to determine how long these refuges will last.</p>
<p>Let’s see this temporary refuge as a gift from the deep sea, offering us an additional period during which the deep populations are sheltered from the effects of global warming. And let’s make the most of this period of respite to understand how these underwater forests function, the mechanisms of resilience, and possibly design restoration interventions.</p>
<p>All this will be of no use, however, if we do not commit to reversing the process of climate change by adopting policies to reduce CO<sub>2</sub> emissions.</p>
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<p><em>UNESCO’s duty remains to reaffirm the humanist missions of education, science and culture. Mobilise education to transform lives; Reconcile with the living; Promote inclusion and mutual understanding; Foster science and technology at the service of humanity are UNESCO’s key strategic objectives.</em></p><img src="https://counter.theconversation.com/content/221146/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lorenzo Bramanti has received funding from Fondation BNP PARIBAS (DEEPLIFE) and COST Action CA20102 Marine Animal Forests of the World (MAF-WORLD). This study is the result of a scientific collaboration between the CNRS, Sorbonne Universitè, Ifremer, Septentrion Environnement and CSIC, with the support of the 1Ocean Foundation and UNESCO as part of the Deep Sea Noah's Ark project.</span></em></p>In the Mediterranean, heat waves are decimating underwater forests that are essential to ecosystems. The gorgonians seem to be better able to resist in the depths, but this refuge may only be temporary.Lorenzo Bramanti, Chargé de Recherches CNRS à l'Observatoire Océanologique de Banyuls, au Laboratoire d'écogéochimie des environnements benthiques, Sorbonne UniversitéLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2146882023-12-19T18:13:36Z2023-12-19T18:13:36ZShipwrecks teem with underwater life, from microbes to sharks<figure><img src="https://images.theconversation.com/files/555600/original/file-20231024-25-xo8h4f.jpg?ixlib=rb-1.1.0&rect=30%2C15%2C5061%2C3534&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A school of grunts on a sunken World War II German submarine in the Atlantic Ocean off North Carolina.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/diver-and-schooling-tomtates-on-wwii-u-352-german-royalty-free-image/153943111">Karen Doody/Stocktrek Images via Getty Images</a></span></figcaption></figure><p>Humans have sailed the world’s oceans for thousands of years, but they haven’t all reached port. Researchers estimate that there are <a href="https://unesdoc.unesco.org/ark:/48223/pf0000152883">some three million shipwrecks</a> worldwide, resting in shallow rivers and bays, coastal waters and the deep ocean. Many sank during catastrophes – some during storms or after running aground, others in battle or collisions with other vessels.</p>
<p>Shipwrecks like <a href="https://www.britannica.com/topic/Titanic">the RMS Titanic</a>, <a href="https://www.britannica.com/topic/Lusitania-British-ship">RMS Lusitania</a> and <a href="https://www.britannica.com/technology/monitor-ship-type#ref51448">USS Monitor</a> conjure tales of human courage and sacrifice, sunken treasure and unsolved mysteries. But there’s another angle to their stories that doesn’t feature humans. </p>
<p>I have <a href="https://scholar.google.com/citations?user=wZ-kv2AAAAAJ&hl=en">studied the biology of shipwrecks</a> in the United States and internationally for 14 years. From this work, I have learned that shipwrecks are not only cultural icons but can also be biological treasures that create habitat for diverse communities of underwater life. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/FTYyzAxt3JI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The USS Monitor, which sank off Cape Hatteras, North Carolina, in a storm on Dec. 31, 1862, is now a center for sea life.</span></figcaption>
</figure>
<p>Recently, I led an international team of biologists and archaeologists in disentangling the mysteries of how this transformation happens. Drawing on scientific advances from our team and international colleagues, our <a href="https://academic.oup.com/bioscience/article-lookup/doi/10.1093/biosci/biad084">new study</a> describes how wrecked vessels can have second lives as seabed habitats.</p>
<h2>A new home for underwater life</h2>
<p>Ships are typically made of metal or wood. When a vessel sinks, it adds foreign, artificial structure to the seafloor. </p>
<p>For example, the World War II tanker <a href="https://monitor.noaa.gov/shipwrecks/clark.html">E.M. Clark</a> sank on a relatively flat, sandy seabed in 1942 when it was torpedoed by a German submarine. To this day, the intact metal wreck looms over the North Carolina seafloor like an underwater skyscraper, creating an island oasis in the sand. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/Bx_uzNvNU1s?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">In this video narrated by NOAA research scientist Avery Paxton, sand tiger sharks hover above the wreck of the E.M. Clark off North Carolina, with vermilion snapper schooling nearby. Jacks and an invasive lionfish also appear.</span></figcaption>
</figure>
<p>The creatures that reside on and around sunken ships are so diverse and abundant that scientists often colloquially call these sites “<a href="https://3d-shipwreck-data-viewer-noaa.hub.arcgis.com/">living shipwrecks</a>.” Marine life ranging from microscopic critters to some of the largest animals in the sea use shipwrecks as homes. Brilliantly colored corals and sponges blanket the wrecks’ surfaces. Silvery schools of baitfish dart and shimmer around the structures, chased by sleek, fast-moving predators. Sharks sometimes cruise around wrecks, likely resting or looking for prey. </p>
<h2>The origin of a second life</h2>
<p>A ship’s transformation from an in-service vessel into a thriving metropolis for marine life can seem like a fairy tale. It has a once-upon-a-time origin story – the wrecking event – and a sequence of life arriving on the sunken structure and beginning to blossom.</p>
<p>Tiny microbes invisible to the naked human eye initially settle on the wreck’s surface, forming a carpet of cells, called a <a href="https://www.britannica.com/science/biofilm">biofilm</a>. This coating helps to <a href="https://doi.org/10.3389/fmars.2019.00048">make the wreck structure suitable</a> for larval animals like sponges and corals to settle and grow there.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Shellfish, deepwater coral and anemones cling to the surface of a sunken wreck." src="https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Diverse sea creatures living on the 19th-century, wooden-hulled Ewing Bank wreck, which lies 2,000 feet (610 meters) deep in the Gulf of Mexico.</span>
<span class="attribution"><a class="source" href="https://oceanexplorer.noaa.gov/explorations/19microbial-stowaways/background/archaeology/media/img2-hires.jpg">NOAA</a></span>
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<p>Larger animals like fish sometimes appear within minutes after a ship sinks. <a href="https://coastalscience.noaa.gov/news/artificial-reefs-may-help-tropical-fish-expand-geographic-range-video/">Small fish</a> hide in the structure’s cracks and crevices, while <a href="https://doi.org/10.1016/j.fooweb.2020.e00147">large sharks</a> glide around it. <a href="https://doi.org/10.1016/j.marenvres.2020.104916">Sea turtles</a> and marine mammals such as <a href="https://doi.org/10.1371/journal.pone.0130581">fur seals</a> have also been spotted on wrecks.</p>
<h2>Hot spots for biodiversity</h2>
<p>Shipwrecks host quantities and varieties of marine life that can make them hot spots for biodiversity. The microbes that transform the wreck structure into habitat also enrich the surrounding sand. Evidence from deep Gulf of Mexico wrecks shows that a <a href="https://doi.org/10.1038/s41396-021-00978-y">halo of increased microbial diversity</a> radiates outward anywhere from 650 to 1,000 feet (200-300 meters) from the wreck. In the Atlantic Ocean, <a href="https://doi.org/10.1111/faf.12548">thousands of grouper</a>, a type of reef fish highly valued by fishers, congregate around and inside shipwrecks.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Fish hover above a wrecked ship's surface." src="https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Groupers and a conger eel, bottom center, on the wreck of the German submarine U-576 off the coast of North Carolina.</span>
<span class="attribution"><a class="source" href="https://oceanexplorer.noaa.gov/explorations/16battlefield/logs/sept7/sept7.html">NOAA</a></span>
</figcaption>
</figure>
<p>Shipwrecks can also serve as stepping stones across the ocean floor that animals use as temporary homes while moving from one location to another. This has been documented in areas of the world with dense concentrations of shipwrecks, such as off North Carolina, where storms and war have sunk hundreds of ships.</p>
<p>In this part of the ocean, popularly known as the “<a href="https://www.ncpedia.org/graveyard-atlantic">Graveyard of the Atlantic</a>,” reef fish likely <a href="https://doi.org/10.1038/s42003-019-0398-2">use the islandlike shipwrecks as corridors</a> when moving north or south away from the equator to find favorable water temperatures as climate change <a href="https://theconversation.com/ocean-heat-is-at-record-levels-with-major-consequences-174760">warms the oceans</a>. Scientists have also observed <a href="https://doi.org/10.1002/ecy.2687">sand tiger sharks</a> traveling from one wreck to another, possibly using the shipwrecks like rest stops during migration.</p>
<p>In the deep sea, life growing on shipwrecks can even generate energy. Tube worms that grow on organic shipwreck materials such as paper, cotton and wood host symbiotic bacteria that produce chemical energy. Such tube worm colonies have been documented in the Gulf of Mexico on the steel <a href="https://www.boem.gov/sites/default/files/boem-newsroom/Library/Ocean-Science/Ocean-Science-Jul-Aug-Sep-2014.pdf">luxury yacht Anona</a>. </p>
<h2>Biological mysteries abound</h2>
<p>Despite their biological value, shipwrecks can also threaten underwater life by altering or destroying natural habitats, causing pollution and spreading invasive species.</p>
<p>When a ship sinks, it can damage existing seafloor habitats. In a well-documented case in the Line Islands of the central Pacific, an <a href="https://doi.org/10.1038/ismej.2011.114">iron shipwreck</a> sank on a healthy coral reef. The iron infusion substantially decreased coral cover, and the reef was overcome by algae.</p>
<p>Ships may carry pollutants as fuel or cargo. As shipwrecks deteriorate in seawater, there is a risk that these pollutants may be released. The <a href="https://doi.org/10.1016/j.marpolbul.2021.112087">level of risk</a> depends on how much of the pollutant the ship was carrying and how intact the wreck is. One recent investigation revealed that effects from shipwreck pollutants can be detected in microbes up to <a href="https://doi.org/10.3389/fmars.2022.1017136">80 years after the wreck</a>.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/JTq4b9c3Z00?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Ships and planes wrecked in wartime can leak toxic materials for decades after they come to rest in the ocean.</span></figcaption>
</figure>
<p>Shipwrecks may also inadvertently assist the spread of invasive plants and animals that wreak biological havoc. Wrecks are new structures that invasive species can settle on, grow and use as a hub to expand to other habitats. <a href="https://doi.org/10.1016/j.marpolbul.2020.111394">Invasive cup coral</a> has spread on World War II shipwrecks off Brazil. In Palmyra Atoll in the Pacific, a type of anemone called a corallimorph <a href="https://doi.org/10.1371/journal.pone.0002989">rapidly invaded</a> a shipwreck and now <a href="https://doi.org/10.1007/s10530-018-1696-1">threatens healthy coral reefs</a>.</p>
<h2>The future of shipwreck exploration</h2>
<p>Shipwrecks create millions of study sites that scientists can use to ask questions about marine life and habitats. One of the greatest challenges is that many wrecks are undiscovered or in remote locations. Advances in technology can help researchers see into the most inaccessible areas of the ocean, not only to find shipwrecks but to better understand their biology. </p>
<p>Maximizing discovery will require biologists, archaeologists and engineers to work together to explore these special habitats. Ultimately, the more we learn, the more effectively we can conserve these historical and biological gems.</p><img src="https://counter.theconversation.com/content/214688/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Avery Paxton is affiliated with NOAA National Centers for Coastal Ocean Science. </span></em></p>When ships sink, they add artificial structures to the seafloor that can quickly become diverse, ecologically important underwater communities.Avery Paxton, Research Marine Biologist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2159772023-10-26T22:16:17Z2023-10-26T22:16:17ZDiscover 6 fascinating animals that live at the bottom of the St. Lawrence River<figure><img src="https://images.theconversation.com/files/554598/original/file-20231016-24-cndzzv.jpg?ixlib=rb-1.1.0&rect=7%2C3%2C2537%2C1912&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Not only do corals inhabit the cold waters of the St. Lawrence, but the species that holds the title of largest marine invertebrate on the planet is present at the entrance to the Gulf.</span> <span class="attribution"><span class="source">(Fisheries and Oceans Canada)</span>, <span class="license">Fourni par l'auteur</span></span></figcaption></figure><p>In the vast St. Lawrence River, an impressive variety of animals live on the seabed. This group of organisms is called benthos. </p>
<p>These organisms live either buried in the sediment (infaunas) or on the surface of the seabed (epibenthos). Benthic invertebrates have no backbone, are not very mobile and are generally small. </p>
<p>And they are far from being rare. As far back as 1988 <a href="https://books.google.ca/books?hl=fr&lr=&id=CoDHrKyVgscC">researchers</a> listed over 1,855 species of benthic invertebrates living in the estuary and gulf of the St. Lawrence River. These represent 84 per cent of all invertebrate species in the St. Lawrence waters. </p>
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<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/469058/original/file-20220615-9549-jj1phn.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em>This article is part of our series, <a href="https://theconversation.com/ca-fr/topics/fleuve-saint-laurent-116908">The St. Lawrence River: In depth</a>.
Don’t miss new articles on this mythical river of remarkable beauty. Our experts look at its fauna, flora and history, and the issues it faces. This series is brought to you by <a href="https://theconversation.com/ca-fr">La Conversation</a>.</em></p>
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<p>Needless to say, many new species have been identified since then, and our knowledge about them continues to grow.</p>
<p>As specialists in benthic ecology, we invite you to discover the benthos through six special features that are certain to pique your curiosity.</p>
<h2>Luminous worms</h2>
<p>Like earthworms in our gardens, marine worms inhabit the ocean floor. They come in all shapes and sizes, and some are even covered in scales. But their originality doesn’t stop there. Some of these worms are actually capable of <a href="https://doi.org/10.11646/ZOOSYMPOSIA.2.1.26">bioluminescence</a>. The production of light in the form of luminous flashes has three general functions: defensive (to escape predators), offensive (in support of predation) and communicative (for reproduction). </p>
<p>In the St. Lawrence River, the only scale worms with this ability are of the <em>Harmothoe</em> genus, of which there are five species. These species can be found on both clay and rocky bottoms in both coastal and deep-water areas.</p>
<h2>Are corals cold?</h2>
<p>For many, oceans bring to mind vacations, heat, diving and coral reefs. But does coral only grow in warm waters? Absolutely not. Some <a href="https://www.dfo-mpo.gc.ca/oceans/ceccsr-cerceef/corals-coraux-eng.html">20 species</a> live in the salty waters of the St. Lawrence ecosystems and this number <a href="https://research.library.mun.ca/12107/1/thesis.pdf">triples</a> if we include the East Coast of Canada. </p>
<p>But what is coral? Corals are actually marine <a href="https://oceanservice.noaa.gov/facts/coral.html">polyps</a>, cylindrical animals with a mouth surrounded by a ring of tentacles, that secrete a molecule called calcium carbonate to form a skeleton. </p>
<p>There are two types: soft corals, with an internal skeleton that reinforces the structure of the <a href="https://oceanservice.noaa.gov/facts/coral.html">colony</a> (a collection of cloned individuals) while ensuring its elasticity, and hard corals, where each polyp secretes a cup-shaped external skeleton, creating their characteristic rigidity. </p>
<p>Not only do corals inhabit the cold waters of the St. Lawrence, but the species that holds the title of largest marine invertebrate on the planet is present at the entrance to the Gulf, notably on the rocky slopes of the Scotian Shelf. This is the <a href="https://www.dfo-mpo.gc.ca/oceans/publications/cs-ce/index-eng.html"><em>Paragorgia arborea</em></a>, some colonies of which can reach six metres in height.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/554072/original/file-20231016-27-sgbiot.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="corals on the seabed" src="https://images.theconversation.com/files/554072/original/file-20231016-27-sgbiot.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/554072/original/file-20231016-27-sgbiot.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554072/original/file-20231016-27-sgbiot.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554072/original/file-20231016-27-sgbiot.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554072/original/file-20231016-27-sgbiot.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554072/original/file-20231016-27-sgbiot.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554072/original/file-20231016-27-sgbiot.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Some colonies of Paragorgia arborea can reach six metres in height.</span>
<span class="attribution"><span class="source">(Fisheries and Oceans Canada)</span>, <span class="license">Fourni par l'auteur</span></span>
</figcaption>
</figure>
<h2>Starfish: dreaded gourmets</h2>
<p>Starfish are so colourful and pretty you can find them in souvenir stores, but don’t be fooled by their appearance. They are actually <a href="https://www.thecanadianencyclopedia.ca/en/article/starfish">fearsome predators</a>, and understanding how they feed will likely change the way you see them. </p>
<p>Faced with the two greediest species in the St. Lawrence (<em>Asterias rubens</em> and <em>Leptasterias polaris</em>), mussels normally have nothing to fear. But thanks to dozens of ambulacral feet — little suckers on their underside — starfish can easily open mussels. As soon as the mussel shows a sign of weakness, the starfish is able to extract its own stomach from its body and insert it into the mussel, where on contact with the flesh, it begins digesting it. In this rather unusual situation the meal can last around 10 hours. Afterwards, the starfish swallows its stomach again and starts hunting for new prey.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/554073/original/file-20231016-27-9kcy6a.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="starfish" src="https://images.theconversation.com/files/554073/original/file-20231016-27-9kcy6a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/554073/original/file-20231016-27-9kcy6a.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=643&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554073/original/file-20231016-27-9kcy6a.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=643&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554073/original/file-20231016-27-9kcy6a.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=643&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554073/original/file-20231016-27-9kcy6a.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=808&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554073/original/file-20231016-27-9kcy6a.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=808&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554073/original/file-20231016-27-9kcy6a.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=808&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Starfish are formidable predators.</span>
<span class="attribution"><span class="source">(Cindy Grant)</span>, <span class="license">Fourni par l'auteur</span></span>
</figcaption>
</figure>
<h2>You said centenarian?</h2>
<p>Present in the Gulf of St. Lawrence, particularly in the Magdalen Islands, the Northern quahog (<em>Arctica islandica</em>) is the world’s longest-living animal. It is a <a href="https://www.dfo-mpo.gc.ca/shellfish-mollusques/identification-eng.htm">bivalve mollusc</a> protected by a calcareous shell with two valves, like that of a mussel or oyster. The Northern quahog can easily live up to 200 years, but the oldest specimen, recorded in Iceland, <a href="https://www.nationalgeographic.com/animals/article/131116-oldest-clam-dead-ming-science-ocean-507">was 507 years old</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/554074/original/file-20231016-27-vxm7uh.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="bivalve mollusc" src="https://images.theconversation.com/files/554074/original/file-20231016-27-vxm7uh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/554074/original/file-20231016-27-vxm7uh.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=533&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554074/original/file-20231016-27-vxm7uh.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=533&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554074/original/file-20231016-27-vxm7uh.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=533&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554074/original/file-20231016-27-vxm7uh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=670&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554074/original/file-20231016-27-vxm7uh.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=670&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554074/original/file-20231016-27-vxm7uh.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=670&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Northern quahog is the world’s longest-living animal.</span>
<span class="attribution"><span class="source">(Lisa Treau De Coeli)</span>, <span class="license">Fourni par l'auteur</span></span>
</figcaption>
</figure>
<p>Other bivalves are known to live long lives. The age of these molluscs can be determined by the growth rings on their shells, rather like trees, but the technique here is called sclerochronology. It is even possible to <a href="https://www.frontiersin.org/articles/10.3389/fmars.2019.00483/full">read the history of the climate</a> on the shells of several bivalves and use this information to predict future conditions.</p>
<h2>Worms, medicine and the Olympics</h2>
<p>Arenicolous worms (<em>Arenicola marina</em>) can be identified by the typical shape of their burrows (a mound of small wiggles), which can be seen at low tide on the St. Lawrence coast.</p>
<p>Although seemingly trivial, these marine worms could enable major advances in medicine thanks to their <a href="https://pubmed.ncbi.nlm.nih.gov/34210070/">hemoglobin</a>, which is capable of transporting up to 50 times more oxygen than that of humans. This particular property enables the worms to store oxygen from seawater at high tide and use this reserve at low tide. </p>
<p><a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8304559/">In medicine</a>, the hemoglobin of the arenicolous worm could be used to improve organ preservation during transplants, to make oxygenating dressings or to develop a blood substitute for emergency transfusions. </p>
<p>Although this worm could revolutionize medicine, it could also pose problems for anti-doping agencies and athletes. Virtually undetectable and hyper-performing, the incredible oxygenating benefits of the arenicolous worm’s hemoglobin could undoubtedly boost athletes’ performance at the next Olympics.</p>
<h2>Natural “crazy glue”</h2>
<p>Although mussels are tossed about by breaking waves all day long, they still manage to hold tight to the rocks. Their secret? The <a href="https://www.nature.com/articles/ncomms14539">byssus</a>, a collection of hair-sized fibres that are both strong and elastic. </p>
<p>The proteins that make up byssus form natural ‘crazy glue’; this liquid glue hardens rapidly, enabling the mussel to adhere with unrivalled tenacity to virtually any surface, even wet ones. </p>
<p>The unusual properties of byssus have fascinated humans since ancient times. In days gone by, these filaments of “marine silk” were used to weave luxurious garments. More recently, the particular chemical composition of the sticky proteins derived from byssal threads has inspired the creation of <a href="https://news.northwestern.edu/stories/2022/03/mussels-synthetic-glue/">underwater adhesives and surgical glues</a>.</p>
<p>In conclusion, while the epifauna of the St. Lawrence is relatively well known, knowledge of the endofauna remains sparse and patchy, even in 2023. Initiatives are underway to discover and characterize this sediment-dwelling fauna. </p>
<p>These studies will undoubtedly lead to the discovery of other exciting facts about the benthos.</p><img src="https://counter.theconversation.com/content/215977/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Philippe Archambault is scientific co-director of the ArcticNet network of centers of excellence, and a member of the Québec Océan strategic cluster, the CNRS/Université Laval International Research Laboratory, Takuvik, and co-director of the 'Ecosystem Functioning and Environmental Protection' axis at the Institut Nordique du Québec.</span></em></p><p class="fine-print"><em><span>Cindy Grant is a member of the Québec-Océan strategic group and of the Unité Mixte Internationale Takuvik.</span></em></p><p class="fine-print"><em><span>Gabrièle Deslongchamps is a member of the Québec-Océan strategic group and of the Unité Mixte Internationale Takuvik.</span></em></p><p class="fine-print"><em><span>Lisa Treau De Coeli is a member of the Québec-Océan strategic group and of the Unité Mixte Internationale Takuvik.</span></em></p>In the vast St. Lawrence River, an impressive variety of animals live on the seabed. This group of organisms is called benthos or benthic invertebrates.Philippe Archambault, Professor & CoScientific Director of ArcticNet, Université LavalCindy Grant, Professionnelle de recherche, biologie marine & écologie benthique, Université LavalGabrièle Deslongchamps, Professionnelle de recherche, Université LavalLisa Treau De Coeli, Professionnelle de recherche en écologie benthique, Université LavalLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2143642023-10-08T19:26:21Z2023-10-08T19:26:21ZThere’s a hidden source of excess nutrients suffocating the Great Barrier Reef. We found it<figure><img src="https://images.theconversation.com/files/551919/original/file-20231003-17-uvt38a.jpg?ixlib=rb-1.1.0&rect=46%2C108%2C5083%2C3337&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Coral impacted by excess nutrients in the Great Barrier Reef.</span> <span class="attribution"><span class="source">Ashly McMahon</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>The Great Barrier Reef is one of Australia’s most important environmental and economic assets. It is estimated to contribute A$56 billion per year and supports about 64,000 full-time jobs, <a href="https://www.barrierreef.org/the-reef/the-value">according to the Great Barrier Reef Foundation</a>. However, the reef is under increasing pressure. </p>
<p>While much public attention is focused on the <a href="https://theconversation.com/severely-threatened-and-deteriorating-global-authority-on-nature-lists-the-great-barrier-reef-as-critical-151275">impacts of climate change</a> on the Great Barrier Reef and the <a href="https://theconversation.com/australian-government-was-blindsided-by-un-recommendation-to-list-great-barrier-reef-as-in-danger-but-its-no-great-surprise-163159">debate around its endangered status</a>, water quality is also crucial to the reef’s health and survival.</p>
<p>Our new study, published today in the journal <a href="https://doi.org/10.1021/acs.est.3c03725.">Environmental Science and Technology</a>, found that previously unquantified groundwater inputs are the largest source of new nutrients to the reef. This finding could potentially change how the Great Barrier Reef is managed.</p>
<h2>Too much of a good thing</h2>
<p>Although nitrogen and phosphorous are essential to support the incredible biodiversity of the reef, <a href="https://www.sciencedirect.com/science/article/abs/pii/S0272771416301469">too much nutrient</a> can lead to losses of coral biodiversity and coverage. It also increases the abundance of algae and the ability of coral larvae to grow into adult coral, and impacts seagrass coverage and health, which is crucial for fisheries and biodiversity. </p>
<p>Nutrient enrichment can also promote the breeding success of <a href="https://link.springer.com/article/10.1007/s00338-010-0628-z">crown-of-thorns starfish</a>, whose increasing populations and voracious appetite for corals have decimated parts of the reef in recent decades. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/551916/original/file-20231003-29-k9m16h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A side by side underwater photo collage of vivid healthy coral and pale murky coral" src="https://images.theconversation.com/files/551916/original/file-20231003-29-k9m16h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/551916/original/file-20231003-29-k9m16h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=200&fit=crop&dpr=1 600w, https://images.theconversation.com/files/551916/original/file-20231003-29-k9m16h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=200&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/551916/original/file-20231003-29-k9m16h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=200&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/551916/original/file-20231003-29-k9m16h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=252&fit=crop&dpr=1 754w, https://images.theconversation.com/files/551916/original/file-20231003-29-k9m16h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=252&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/551916/original/file-20231003-29-k9m16h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=252&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pristine coral and coral affected by excess nutrient in the Great Barrier Reef.</span>
<span class="attribution"><span class="source">Ashly McMahon</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>What are the sources of nutrients driving the degradation of the reef? Previous studies have <a href="https://www.reefplan.qld.gov.au/__data/assets/pdf_file/0031/45994/2017-scientific-consensus-statement-summary-chap02.pdf">focused on river discharge</a>. According to one estimate, there has been a <a href="https://www.sciencedirect.com/science/article/abs/pii/S0025326X11005583">fourfold increase in riverine nutrient</a> input to the Great Barrier Reef since pre-industrial times.</p>
<p>This past focus on rivers has emphasised reducing surface water nutrient inputs through changing regulations for land-clearing and agriculture, while neglecting other potential sources. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/floods-of-nutrients-from-fertilisers-and-wastewater-trash-our-rivers-could-offsetting-help-203235">Floods of nutrients from fertilisers and wastewater trash our rivers. Could offsetting help?</a>
</strong>
</em>
</p>
<hr>
<p>However, the most recent nutrient budget for the Great Barrier Reef found river-derived nutrient inputs can account for only a <a href="https://www.sciencedirect.com/science/article/abs/pii/S0278434311003025">small proportion of the nutrients</a> necessary to support the abundant life in the reef. This imbalance suggests large, unidentified sources of nutrients to the reef. Not knowing what these are may lead to ineffective management approaches.</p>
<p>With recent government funding of <a href="https://www.barrierreef.org/what-we-do/reef-trust-partnership">more than $200 million to tackle water quality on the reef</a> which is largely focused on managing river water inputs, it is crucial to make sure other nutrient sources are not overlooked.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/551905/original/file-20231003-19-ayf7sc.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram listing nutrient sources to the reef" src="https://images.theconversation.com/files/551905/original/file-20231003-19-ayf7sc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/551905/original/file-20231003-19-ayf7sc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=270&fit=crop&dpr=1 600w, https://images.theconversation.com/files/551905/original/file-20231003-19-ayf7sc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=270&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/551905/original/file-20231003-19-ayf7sc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=270&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/551905/original/file-20231003-19-ayf7sc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=339&fit=crop&dpr=1 754w, https://images.theconversation.com/files/551905/original/file-20231003-19-ayf7sc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=339&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/551905/original/file-20231003-19-ayf7sc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=339&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The source of potential groundwater inputs to the Great Barrier Reef.</span>
<span class="attribution"><span class="source">Douglas Tait</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>We found a new nutrient source</h2>
<p>Our research team decided to try and track down this missing source of nutrients.</p>
<p>We used natural tracers to track groundwater inputs off Queensland’s coast. This allows us to quantify how much invisible groundwater flows into the Great Barrier Reef, along with the nutrients hitching a ride with this water. Our findings indicate that current efforts to preserve and restore the health of the reef may require a new perspective.</p>
<p>Our team collected data from offshore surveys, rivers and coastal bores along the coastline from south of Rockhampton to north of Cairns. We used the natural groundwater tracer radium to track how much nutrient is transported from the land and shelf sediments via invisible groundwater flows.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-a-disgruntled-scientist-looking-to-prove-his-food-wasnt-fresh-discovered-radioactive-tracers-and-won-a-nobel-prize-80-years-ago-214784">How a disgruntled scientist looking to prove his food wasn't fresh discovered radioactive tracers and won a Nobel Prize 80 years ago</a>
</strong>
</em>
</p>
<hr>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/551907/original/file-20231003-19-ves2t4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A blue and white ship sailing on a calm ocean" src="https://images.theconversation.com/files/551907/original/file-20231003-19-ves2t4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/551907/original/file-20231003-19-ves2t4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/551907/original/file-20231003-19-ves2t4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/551907/original/file-20231003-19-ves2t4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/551907/original/file-20231003-19-ves2t4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/551907/original/file-20231003-19-ves2t4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/551907/original/file-20231003-19-ves2t4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The AIMS research vessel, Cape Ferguson.</span>
<span class="attribution"><span class="source">Ashly McMahon</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>We found that groundwater discharge was 10–15 times greater than river inputs. This meant roughly one-third of new nitrogen and two-thirds of phosphorous inputs came via groundwater discharge. This was nearly twice the amount of nutrient delivered by river waters.</p>
<p>Past investigations have revealed that groundwater discharge delivers nutrients and affects water quality in a <a href="https://www.nature.com/articles/s43017-021-00152-0">diverse range of coastal environments</a>, including estuaries, coral reefs, coastal embayments and lagoons, intertidal wetlands such as mangroves and saltmarshes, the continental shelf and even the global ocean.</p>
<p>In some cases, this can account for <a href="https://aslopubs.onlinelibrary.wiley.com/doi/abs/10.4319/lo.2011.56.2.0673">90% of the nutrient inputs</a> to coastal areas, which has major implications for global biologic production. </p>
<p>Nevertheless, this pathway remains overlooked in most coastal nutrient budgets and water quality models.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/551909/original/file-20231003-29-npys7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A beach early in the morning with people digging into the sand" src="https://images.theconversation.com/files/551909/original/file-20231003-29-npys7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/551909/original/file-20231003-29-npys7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=339&fit=crop&dpr=1 600w, https://images.theconversation.com/files/551909/original/file-20231003-29-npys7a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=339&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/551909/original/file-20231003-29-npys7a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=339&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/551909/original/file-20231003-29-npys7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=426&fit=crop&dpr=1 754w, https://images.theconversation.com/files/551909/original/file-20231003-29-npys7a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=426&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/551909/original/file-20231003-29-npys7a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=426&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The research team sampling groundwater near the Great Barrier Reef.</span>
<span class="attribution"><span class="source">Ashly McMahon</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>A paradigm shift needed?</h2>
<p>Our results suggest the need for a strategic <a href="https://niwa.co.nz/our-science/freshwater/tools/kaitiaki_tools/land-use/agriculture/mitigation">shift in management approaches</a> aimed at safeguarding the Great Barrier Reef from the effects of excess nutrients.</p>
<p>This includes better land management practices to ensure fewer nutrients are entering groundwater aquifers. We can also use ecological (such as seaweed and bivalve aquaculture, enhancing seagrass, oyster reefs, mangroves and salt marsh) and hydrological (increasing flushing where possible) practices at groundwater discharge hotspots to <a href="https://www.frontiersin.org/articles/10.3389/fmars.2018.00470/full">reduce excess nutrients in the water column</a>. </p>
<p><a href="https://medium.com/water-food-nexus/water-recycling-and-reuse-in-agriculture-for-circularity-of-food-and-water-f08fe4b131b3">The reuse of nutrient-rich groundwater</a> for agriculture also needs to be explored as it represents an untapped and inexpensive nutrient source.</p>
<p>Importantly, unlike river outflow, nutrients in groundwater can be <a href="https://www.sciencedirect.com/science/article/abs/pii/S004896972035539X">stored underground for decades</a> before being discharged into coastal waters. This means research and strategies to protect the reef need to be long-term. The potential large lag time may lead to significant problems in the coming decades as the nutrients now stored in underground aquifers make their way to coastal waters regardless of changes to current land use practices.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/551908/original/file-20231003-17-z4u9tf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A vivid landscape of colourful corals in an underwater photo" src="https://images.theconversation.com/files/551908/original/file-20231003-17-z4u9tf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/551908/original/file-20231003-17-z4u9tf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/551908/original/file-20231003-17-z4u9tf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/551908/original/file-20231003-17-z4u9tf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/551908/original/file-20231003-17-z4u9tf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/551908/original/file-20231003-17-z4u9tf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/551908/original/file-20231003-17-z4u9tf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pristine corals on the Great Barrier Reef.</span>
<span class="attribution"><span class="source">Ashly McMahon</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The understanding and ability to manage the sources of nutrients is pivotal in preserving global coral reef systems.</p>
<p>While we need to reduce the impact of climate change on this fragile ecosystem, we also need to adjust our policies to manage nutrient inputs and safeguard the Great Barrier Reef for generations to come.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/out-of-danger-because-the-un-said-so-hardly-the-barrier-reef-is-still-in-hot-water-210787">Out of danger because the UN said so? Hardly – the Barrier Reef is still in hot water</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/214364/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors receive funding from the Australian Research Council, the Herman Slade Foundation and the Great Barrier Reef Foundation. </span></em></p><p class="fine-print"><em><span>Damien Maher receives funding from the Australian Research Council, Hermon Slade Foundation, Great Barrier Reef Foundation. </span></em></p>While the Great Barrier Reed needs nutrients to support the ecosystem, it is possible to have too much of a good thing.Douglas Tait, Senior Researcher, Southern Cross UniversityDamien Maher, Professor, Southern Cross UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2128492023-09-20T21:09:33Z2023-09-20T21:09:33ZSex life discovery raises IVF hope for endangered purple cauliflower soft coral<figure><img src="https://images.theconversation.com/files/549271/original/file-20230920-25-omlgkz.jpg?ixlib=rb-1.1.0&rect=7%2C27%2C1650%2C2293&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">David Harasti</span></span></figcaption></figure><p>Vital coastal habitat was destroyed in the devastating floods that hit New South Wales in 2021 and 2022. </p>
<p>The purple cauliflower soft coral <em>Dendronephthya australis</em>, now listed as an endangered species, was almost completely wiped out in the Port Stephens estuary and along the coast. That’s a tragedy because this coral shelters young snapper and the endangered White’s seahorse. </p>
<p>Unfortunately, a lack of knowledge hampered recovery efforts – until now. </p>
<p>In <a href="https://doi.org/10.1007/s00227-023-04298-x">our new research</a> we discovered how the coral reproduces. We used IVF (in-vitro fertilisation) to create baby coral in the lab. And we successfully transplanted the coral into the wild. This offers new hope for the survival of the species. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/tOIFmMCRU3I?wmode=transparent&start=58" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Understanding the sex life of purple cauliflower soft coral offers hope for the species.</span></figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/beautiful-rare-purple-cauliflower-coral-off-nsw-coast-may-be-extinct-within-10-years-160184">Beautiful, rare 'purple cauliflower' coral off NSW coast may be extinct within 10 years</a>
</strong>
</em>
</p>
<hr>
<h2>Variety is the spice of life</h2>
<p>Corals have a complicated sex life. There’s more than one way to “do it”. And gender varies too. </p>
<p>Corals can reproduce asexually, meaning they create genetic copies of themselves. This process often entails shedding polyps that can attach to reefs to form new colonies. </p>
<p>Using this process is a common approach for coral restoration. It’s a bit like propagating plants. Cuttings or fragments are removed from adult colonies, briefly maintained in the lab, and then new corals are transplanted into the wild. This isn’t a simple process for soft corals, though we have been exploring <a href="https://doi.org/10.1002/aqc.3895">ways to make this work</a> for <em>Dendronephthya australis</em>.</p>
<p>Many corals are hermaphrodites, which means they have both male and female reproductive organs. Others form colonies that are entirely male or female. And some mix or swap sexes. </p>
<p>Spawning is the release of eggs and sperm. Again, corals can use various techniques. Broadcast spawning is where eggs and sperm are released into the water column. Brooding is where eggs are fertilised within colonies and later released as larvae. </p>
<p>But until sexual reproduction of an individual species is observed, their sex life remains a private matter.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/548615/original/file-20230916-27-tj4s7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Graphic illustrating the life cycle of the purple cauliflower coral, which begins with an egg being fertilised by sperm, to embryo cell division within 2-4 hours, to fully grown larvae by day 5, to metamorphosis to polyp from 8 days of age." src="https://images.theconversation.com/files/548615/original/file-20230916-27-tj4s7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548615/original/file-20230916-27-tj4s7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548615/original/file-20230916-27-tj4s7a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548615/original/file-20230916-27-tj4s7a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548615/original/file-20230916-27-tj4s7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548615/original/file-20230916-27-tj4s7a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548615/original/file-20230916-27-tj4s7a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The life cycle of the purple cauliflower coral <em>Dendronephthya australis</em> begins with an egg being fertilised by sperm, proceeds to embryo cell division within 2-4 hours, to fully grown larvae by day 5, to metamorphosis to polyp from 8 days of age.</span>
<span class="attribution"><span class="source">Meryl Larkin</span></span>
</figcaption>
</figure>
<h2>A chance discovery in the lab</h2>
<p>We were growing coral in the lab, raising asexual clones from fragments, when we noticed something unusual. </p>
<p>There were small orange dots inside some of the corals. These were much larger than the grains of dry orange “coral food” we fed them. So they had to be something else. </p>
<p>We soon realised the orange dots were unfertilised eggs. Half of the fragments in our care contained eggs. As sperm is much smaller, we had to sacrifice small portions of the remaining coral fragments for closer inspection of their contents (under a microscope). In doing this, we discovered the other half were sperm-bearing. </p>
<p>As fate would have it, we had collected fragments from two donor colonies – one female and one male. By chance, we discovered <em>Dendronephthya australis</em> is “gonochoric” (meaning colonies are either male or female). </p>
<p>We watched the corals carefully over the following weeks and made more discoveries. Females spawned (released their eggs) around the “neap tide” (when the moon appears half full) during the summer months. </p>
<p>Maybe the coral evolved to spawn when tidal currents are slowest, to maximise the chance of fertilisation. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/548616/original/file-20230916-27-8l7r3c.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A closeup photo of a soft coral fragment containing unfertilised eggs (orange dots)" src="https://images.theconversation.com/files/548616/original/file-20230916-27-8l7r3c.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548616/original/file-20230916-27-8l7r3c.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=470&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548616/original/file-20230916-27-8l7r3c.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=470&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548616/original/file-20230916-27-8l7r3c.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=470&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548616/original/file-20230916-27-8l7r3c.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=591&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548616/original/file-20230916-27-8l7r3c.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=591&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548616/original/file-20230916-27-8l7r3c.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=591&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Unfertilised eggs (orange dots) were observed in <em>Dendronephthya australis</em> fragments for the first time.</span>
<span class="attribution"><span class="source">Meryl Larkin</span></span>
</figcaption>
</figure>
<h2>Coral IVF for making babies</h2>
<p>We used IVF techniques to fertilise harvested eggs. Cell division occurred within hours. Mobile larvae grew over the following week. </p>
<p>From eight days of age, the larvae started to transform into polyps; we were the first people to witness these tiny cauliflower coral babies (as single polyps).</p>
<p>Within just a few weeks, we had produced 280 babies from just a few coral fragments. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/548617/original/file-20230916-29-f94gns.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A closeup photo showing baby single coral polyps after metamorphosis from the larval stage" src="https://images.theconversation.com/files/548617/original/file-20230916-29-f94gns.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548617/original/file-20230916-29-f94gns.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=429&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548617/original/file-20230916-29-f94gns.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=429&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548617/original/file-20230916-29-f94gns.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=429&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548617/original/file-20230916-29-f94gns.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=539&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548617/original/file-20230916-29-f94gns.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=539&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548617/original/file-20230916-29-f94gns.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=539&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Researchers achieved larval settlement, witnessing the change to the single polyp stage of the soft coral.</span>
<span class="attribution"><span class="source">David Harasti</span></span>
</figcaption>
</figure>
<p>Understanding how the purple cauliflower coral reproduces is important for several reasons:</p>
<ul>
<li><p>maintaining genetic diversity: if the sex ratio becomes unbalanced, the effective population size will be lower than the total number of remaining individuals</p></li>
<li><p>achieving fertilisation: broadcast spawning in corals is density-dependent. That means if more colonies are lost, the chance of natural sexual reproduction decreases </p></li>
<li><p>restoring gender balance: any attempt to grow more coral from fragments will need to ensure both male and female colonies are represented </p></li>
<li><p>scaling up production: sexual reproduction provides an opportunity to raise more baby corals while maintaining genetic diversity in the population. </p></li>
</ul>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/548618/original/file-20230916-29-ebwo29.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo of a Four-month-old juvenile coral transplanted in Port Stephens" src="https://images.theconversation.com/files/548618/original/file-20230916-29-ebwo29.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548618/original/file-20230916-29-ebwo29.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=475&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548618/original/file-20230916-29-ebwo29.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=475&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548618/original/file-20230916-29-ebwo29.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=475&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548618/original/file-20230916-29-ebwo29.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=597&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548618/original/file-20230916-29-ebwo29.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=597&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548618/original/file-20230916-29-ebwo29.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=597&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Four-month-old juvenile coral transplanted in Port Stephens.</span>
<span class="attribution"><span class="source">Meryl Larkin</span></span>
</figcaption>
</figure>
<h2>Ongoing restoration work</h2>
<p>Since this discovery, we have successfully repeated these IVF techniques. We transplanted hundreds of coral babies and released thousands of larvae back into Port Stephens. </p>
<p>Early results suggest some IVF babies survived at least the first 18 months and performed better than the asexual fragments.</p>
<p>We plan to implement the IVF program annually. We’re optimistic that we can boost the population of this endangered coral in ways never thought possible.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/coral-meet-coral-how-selective-breeding-may-help-the-worlds-reefs-survive-ocean-heating-166412">Coral, meet coral: how selective breeding may help the world's reefs survive ocean heating</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/212849/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Meryl Larkin receives funding from the NSW Department of Primary Industries, Southern Cross University’s National Marine Science Centre and Marine Ecology Research Centre, and the Australian Government Research Training Program. Ongoing work (subsequent to Meryl Larkin's PhD project) has been supported with funding from the NSW Environmental Trust. </span></em></p><p class="fine-print"><em><span>David Harasti received funding from the NSW Environmental Trust to implement recovery actions for the endangered soft coral.</span></em></p><p class="fine-print"><em><span>Kirsten Benkendorff, Stephen D. A. Smith, and Tom R Davis do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>After a chance discovery in the lab, this team used IVF to make hundreds of coral babies for restoration projects in New South Wales. So far the IVF babies are doing well in the wild.Meryl Larkin, PhD Candidate, Southern Cross UniversityDavid Harasti, Adjunct assistant professor, Southern Cross UniversityKirsten Benkendorff, Professor, Southern Cross UniversityStephen D. A. Smith, Professor of Marine Science, National Marine Science Centre, Southern Cross UniversityTom R Davis, Research Scientist - Marine Climate Change, Hunter New England Local Health DistrictLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2110072023-08-23T21:22:36Z2023-08-23T21:22:36ZCoral reefs: How climate change threatens the hidden diversity of marine ecosystems<figure><img src="https://images.theconversation.com/files/543317/original/file-20230817-23-tvw75n.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3982%2C2976&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A healthy reef on Kiritimati (Christmas Island, Republic of Kiribati).</span> <span class="attribution"><span class="source">(Danielle Claar)</span>, <span class="license">Author provided</span></span></figcaption></figure><iframe style="width: 100%; height: 100px; border: none; position: relative; z-index: 1;" allowtransparency="" allow="clipboard-read; clipboard-write" src="https://narrations.ad-auris.com/widget/the-conversation-canada/coral-reefs-how-climate-change-threatens-the-hidden-diversity-of-aquatic-ecosystems" width="100%" height="400"></iframe>
<p>Like the heat waves on land we have all grown familiar with, <a href="https://doi.org/10.1146/annurev-marine-032720-095144">marine heat waves</a> are being <a href="https://doi.org/10.1038/s41586-018-0383-9">amplified by climate change</a>. These extreme warm water events have <a href="https://doi.org/10.1038/s41558-019-0412-1">ushered in some of the most catastrophic impacts</a> of climate change and are now a major threat to ocean life. </p>
<p>Coral reefs, which are <a href="https://doi.org/10.1017/9781009157964.001">home to a quarter of all life in the ocean, are the most vulnerable</a>.
This is a dire situation, given the vast number of people who <a href="https://doi.org/10.1016/j.rsma.2019.100699">depend on coral reefs</a> for their sustenance and livelihoods. </p>
<p>As climate change pushes corals beyond their limits, a key question is <a href="https://doi.org/10.1016/j.cub.2017.04.047">why different corals vary in their sensitivity</a> to warm waters. </p>
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<img alt="" src="https://images.theconversation.com/files/542485/original/file-20230813-167275-4irzrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/542485/original/file-20230813-167275-4irzrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/542485/original/file-20230813-167275-4irzrr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/542485/original/file-20230813-167275-4irzrr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/542485/original/file-20230813-167275-4irzrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/542485/original/file-20230813-167275-4irzrr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/542485/original/file-20230813-167275-4irzrr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">A reef on Kiritimati (Christmas Island) at the end of the 2015-16 marine heat wave where some Porites lobata colonies survived (yellow/tan colours), some were alive but bleached (white colonies), and some died along with the rest of the reef (red/purple/pink colours of turf algae covering dead colonies). (Danielle Claar), Author provided.</span>
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<p>In our <a href="https://doi.org/10.1126/sciadv.adf0954">new study in <em>Science Advances</em></a>, we examined the genetics of hundreds of individual corals during the 2015-16 El Niño-driven heat wave. Our results suggest that heat waves have hidden impacts on the genetic composition of reef-building corals. Understanding this could help scientists bolster reef resilience to future heat waves. </p>
<h2>Pushing corals out of their comfort zones</h2>
<p>Corals are <a href="https://doi.org/10.1126/science.aan8048">highly adapted to the temperature</a> of their local waters, with temperatures even 1 C warmer than normal pushing them out of their comfort zone. </p>
<p>Unusually warm water <a href="https://doi.org/10.1146/annurev.ecolsys.34.011802.132417">disrupts the vital relationship</a> between stony corals (the reef-builders) and their symbiotic partners, microscopic algae that provide food to the corals. This causes coral bleaching, and in many cases mortality. </p>
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Read more:
<a href="https://theconversation.com/is-the-great-barrier-reef-reviving-or-dying-heres-whats-happening-beyond-the-headlines-210558">Is the Great Barrier Reef reviving – or dying? Here's what's happening beyond the headlines</a>
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<p>The tropical heat wave at our study site in the central Pacific Ocean, Kiritimati (Christmas Island), lasted for ten months, a world record. This led to extensive coral bleaching, presenting an opportunity to determine why some corals died and others survived. </p>
<h2>Cryptic diversity within a widespread coral species</h2>
<p>We focused on the widespread lobed coral (<em>Porites lobata</em>). This species is amongst the most heat-tolerant corals, and despite <a href="https://doi.org/10.1126/sciadv.abq5615">almost 90 per cent of all coral cover being lost</a> on Kiritimati, over half of lobed corals survived. </p>
<p>In fact, some <em>Porites</em> colonies didn’t bleach at all. </p>
<p>Why?</p>
<p>Using genomic tools, we identified three distinct types of <em>Porites lobata</em> on Kiritimati. These lineages, which may represent distinct species, are indistinguishable by eye but genetically different. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/542847/original/file-20230815-29-rh83z4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/542847/original/file-20230815-29-rh83z4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/542847/original/file-20230815-29-rh83z4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/542847/original/file-20230815-29-rh83z4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/542847/original/file-20230815-29-rh83z4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/542847/original/file-20230815-29-rh83z4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/542847/original/file-20230815-29-rh83z4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Two colonies of Porities growing side-by-side on Kiritimati (Christmas Island) during the 2015-16 marine heat wave. One colony appears healthy while the other is severely bleached. (Kieran Cox), Author provided.</span>
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<p>Such biodiversity is known as <a href="https://doi.org/10.1186/jbiol60">“cryptic diversity” or “hidden diversity.”</a> Although cryptic diversity is widespread across corals, its ecological implications remain unclear. </p>
<h2>Marine heat waves threaten cryptic diversity</h2>
<p>We found that one genetic lineage of <em>Porites</em> was highly sensitive to the heat wave: only 15 per cent of its colonies survived compared to 50-60 per cent in the other lineages. Thus, even in a coral widely considered to be stress tolerant, heat waves can have hidden impacts, threatening diversity that is invisible to the naked eye.</p>
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Read more:
<a href="https://theconversation.com/out-of-danger-because-the-un-said-so-hardly-the-barrier-reef-is-still-in-hot-water-210787">Out of danger because the UN said so? Hardly – the Barrier Reef is still in hot water</a>
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<p>If future marine heat waves continue to have similar effects, eventually sensitive genotypes like this one could be completely lost, reducing the genetic diversity of coral reefs. </p>
<p>Because interbreeding between cryptic lineages and species can offer a <a href="https://doi.org/10.1046/j.1365-294x.2001.01216.x">potential avenue for future adaptation</a>, losses of genetic diversity could make a bad problem even worse by limiting future adaptation to changing environments.</p>
<h2>A forced breakup</h2>
<p>So why did <em>Porites</em> lineages on Kiritimati differ in survival? </p>
<p>One hypothesis is that they house symbiotic partners with different heat sensitivities. Using metabarcoding, a technique that attempts to identify everything found living in the coral tissue, we identified which symbionts were partnered with which corals before, during and after the heat wave.</p>
<p>We found that the distinct <em>Porites</em> lineages had different partnerships before the heat wave. <em>Porites</em> species pass on their symbionts from <a href="https://doi.org/10.1111/j.1529-8817.2012.01220.x">one generation to the next</a> and so these relationships likely arose over many generations.</p>
<figure class="align-center ">
<img alt="two divers inspect a coral reef" src="https://images.theconversation.com/files/543319/original/file-20230817-29-myzq3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/543319/original/file-20230817-29-myzq3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/543319/original/file-20230817-29-myzq3d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/543319/original/file-20230817-29-myzq3d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/543319/original/file-20230817-29-myzq3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/543319/original/file-20230817-29-myzq3d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/543319/original/file-20230817-29-myzq3d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Danielle Claar and a team member sample a tracked surviving colony at the end of the heat wave on Kiritimati (Christmas Island).</span>
<span class="attribution"><span class="source">(Julia K. Baum), Author provided.</span></span>
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<p>By the end of the heat wave, however, one of <em>Porites’</em> unique algal partners had been virtually eliminated. The survivors of all lineages had similar symbionts, suggesting specialized relationships between the partners had been lost under extreme temperatures. </p>
<p>Thus, not only was a cryptic coral lineage left teetering on the edge of local extinction, but its specialized symbiotic relationship had also been forcefully broken up.</p>
<h2>Implications for conserving coral reefs</h2>
<p>Due to climate change and other threats, we are currently experiencing a <a href="https://doi.org/10.1038/35002708">biodiversity crisis</a>. Our findings underscore that this crisis extends beyond what the eye can see.</p>
<p>Cryptic species often occupy <a href="https://doi.org/10.1111/1365-2664.12246">unique ecological niches and play specific roles within ecosystems</a>. Discovering these hidden differences can enhance our understanding of how ecosystems function. But worryingly, we may be losing this critical diversity before it is even discovered. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/through-the-magnifying-glass-how-cutting-edge-technology-is-helping-scientists-understand-baby-corals-210372">Through the magnifying glass: how cutting-edge technology is helping scientists understand baby corals</a>
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<p>Continued study of cryptic diversity could prove essential to building climate resilient ecosystems. Using heat tolerant cryptic lineages in <a href="https://doi.org/10.3389/fmars.2020.00237">restoration approaches</a>, for example, could help make reefs more tolerant to future warming. </p>
<p>Ultimately, <a href="https://doi.org/10.1126/science.aaw6974">greenhouse gas emissions must be rapidly reduced to curb planetary warming</a>. While targeted efforts to bolster coral reefs against climate change may buy limited time, the current heat waves blanketing the world’s oceans underscore that the ocean is simply becoming too hot for corals and we need to act rapidly to mitigate the damage.</p><img src="https://counter.theconversation.com/content/211007/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Samuel Starko receives funding from the Forrest Research Foundation, The University of Western Australia, The Australian Research Council (ARC), and Revive & Restore.</span></em></p><p class="fine-print"><em><span>Julia K. Baum receives funding from the Natural Sciences and Engineering Research Council of Canada (NSERC), the U.S. National Science Foundation (NSF), the David and Lucile Packard Foundation, the Rufford Maurice Laing Foundation, the Canadian Foundation for Innovation, British Columbia Knowledge Development Fund, University of Victoria, The Pew Charitable Trusts, and the National Geographic Society.
</span></em></p>Exploring the often unseen, and poorly understood, nuances of diversity within coral reefs may prove essential for ensuring the long-term health of Earth’s oceans.Samuel Starko, Forrest Research Fellow, The University of Western AustraliaJulia K. Baum, Professor of Biology, University of VictoriaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2118522023-08-22T14:24:09Z2023-08-22T14:24:09ZRemote Pacific coral reef shows at least some ability to cope with ocean warming – new study<figure><img src="https://images.theconversation.com/files/543575/original/file-20230820-225972-21eyt4.jpeg?ixlib=rb-1.1.0&rect=0%2C13%2C1736%2C1101&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A healthy coral reef in Palau in the western Pacific Ocean.</span> <span class="attribution"><span class="source">Liam Lachs</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Unprecedented ocean temperatures are triggering mass coral bleaching events across the <a href="https://coralreefwatch.noaa.gov/satellite/bleachingoutlook_cfs/weekly_90.php">world</a>. This year, the world’s third largest barrier reef, in Florida, is already being <a href="https://twitter.com/AFP/status/1685299136764280833">hit hard</a>.</p>
<p>New research by my colleagues and I offers a glimmer of hope: coral reefs we studied in the Pacific appear to have increased their resistance to high ocean temperatures. But this can only improve their long-term futures if there is strong global action on reducing carbon emissions.</p>
<p>We know that corals will need to withstand rising ocean temperatures to survive under climate change. And we know reef-building corals are acutely sensitive to even small increases in temperature. What we don’t yet know is whether their “thermal tolerance” – essentially their ability to handle high temperatures – can keep pace with ocean warming.</p>
<p>In normal conditions, corals live in symbiosis with microscopic algae housed within their tissue. These algae give corals their <a href="https://theconversation.com/revealed-why-some-corals-are-more-colourful-than-others-36866">beautiful colours</a>, and provide them with food through photosynthesis, just like plants (corals are animals, don’t forget). </p>
<p>However, this relationship <a href="https://www.cell.com/current-biology/pdf/S0960-9822(20)31591-8.pdf">breaks down when it’s too hot</a>: the microalgae are expelled, leaving the corals stark white, or bleached, which usually leads to death. Extreme temperatures can even kill corals outright, bypassing the gradual bleaching process.</p>
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<a href="https://images.theconversation.com/files/543509/original/file-20230818-15-ee0qxl.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="bleached coral" src="https://images.theconversation.com/files/543509/original/file-20230818-15-ee0qxl.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/543509/original/file-20230818-15-ee0qxl.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/543509/original/file-20230818-15-ee0qxl.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/543509/original/file-20230818-15-ee0qxl.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/543509/original/file-20230818-15-ee0qxl.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/543509/original/file-20230818-15-ee0qxl.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/543509/original/file-20230818-15-ee0qxl.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Mass bleaching in the Maldives in 2016 which led to many corals dying.</span>
<span class="attribution"><a class="source" href="https://link.springer.com/chapter/10.1007/978-3-030-20389-4_13">Stephen Bergacker</a>, <span class="license">Author provided</span></span>
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<p>In our new study published in <a href="https://doi.org/10.1038/s41467-023-40601-6">Nature Communications</a> on the coral reefs of Palau, a nation of more than 300 small islands in the western Pacific Ocean, we found that the tolerance of corals to warm conditions has likely increased over the past three decades.</p>
<h2>Testing thermal tolerance</h2>
<p>Palau experienced intense marine heatwaves in 1998, 2010 and 2017, but interestingly, each successive event led to less coral bleaching. Such a phenomenon has also been recorded in <a href="https://www.sciencedirect.com/science/article/pii/S0960982221014901">Australia’s Great Barrier Reef</a>, <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0033353">south-east Asia</a>, and <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0070443">French Polynesia</a>. </p>
<p>Is this evidence that coral communities are adapting to hotter temperatures? We set out to test whether thermal tolerance has likely increased for at least those reefs in Palau, and if so, how quickly. </p>
<p>Our international team of researchers designed a simulation study, drawing on 35 years of sea surface temperature data and historic observations of bleaching. We found that the thermal tolerance of the coral communities in Palau has likely increased at 0.1°C/decade. That’s slightly less than the increase in global temperatures (about <a href="https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature">0.18°C/decade</a>) but does suggest these coral reefs have an innate capacity for climate resilience.</p>
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<a href="https://images.theconversation.com/files/543578/original/file-20230820-153592-nwaj3l.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="scuba diver above coral reef" src="https://images.theconversation.com/files/543578/original/file-20230820-153592-nwaj3l.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/543578/original/file-20230820-153592-nwaj3l.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/543578/original/file-20230820-153592-nwaj3l.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/543578/original/file-20230820-153592-nwaj3l.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/543578/original/file-20230820-153592-nwaj3l.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/543578/original/file-20230820-153592-nwaj3l.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/543578/original/file-20230820-153592-nwaj3l.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Researcher conducting a 3D mapping survey of a coral reef in Palau.</span>
<span class="attribution"><span class="source">Eveline van der Steeg</span>, <span class="license">Author provided</span></span>
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<h2>How coral reefs are adapting to warmer oceans</h2>
<p>More work is needed to pin down exactly what has happened, but there are various mechanisms that could explain this. </p>
<p>One involves the turnover of species. There are hundreds of different coral species, each with a <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/j.1461-0248.2012.01861.x?casa_token=8vXhQAvJA0cAAAAA:6E3XAgHUbuzWIXTrFc3Cq6mCXOI1w7cG8RrgsUb0tLnrOfYZK2aMenY5wMlsBb7Cg_EbafteVgUyVn0">unique evolutionary history and life strategy</a>. Some, like branching <em>Acropora</em>, are fast-growing yet sensitive to temperature, while others, like massive <em>Porites</em>, are slow-growing but more stress tolerant. </p>
<p>Severe heatwaves can weed out the sensitive species, leaving the coral reef dominated by the tougher ones, which can compromise important ecological functions like reef growth and habitat provision for seafood species.</p>
<p>The second mechanism is genetic adaptation. Thermal tolerance is a complex trait that is likely <a href="https://www.frontiersin.org/articles/10.3389/fmars.2017.00434/full">influenced by thousands of genes</a>, but most corals only have some of these. Following Darwin’s theory of survival of the fittest, natural selection can choose the winners under climate change. Over multiple generations and many rounds of selection, thermal tolerance genes can become more prevalent, and thus increase the thermal tolerance of species populations.</p>
<p>The final explanation involves individual acclimatisation. Even within the lifetime of a single coral, its ability to survive thermal stress events can change. As the saying goes, “<a href="https://www.the-scientist.com/features/environmental-memory-how-corals-are-adjusting-to-warmer-waters-69640">what doesn’t kill you makes you stronger</a>”, and so, being exposed to low-level thermal stress can later improve chances of survival under high-level thermal stress.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/543589/original/file-20230821-229778-hhvlx0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Three photos of corals" src="https://images.theconversation.com/files/543589/original/file-20230821-229778-hhvlx0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/543589/original/file-20230821-229778-hhvlx0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/543589/original/file-20230821-229778-hhvlx0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/543589/original/file-20230821-229778-hhvlx0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/543589/original/file-20230821-229778-hhvlx0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/543589/original/file-20230821-229778-hhvlx0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/543589/original/file-20230821-229778-hhvlx0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">a) Community of corals with high species diversity; b) two corals of the same species with contrasting bleaching susceptibility; c) the symbiotic microalgal community housed within coral tissues.</span>
<span class="attribution"><a class="source" href="https://www.oist.jp/image/coral-polyps-and-their-symbionts">Liam Lachs; Laurie Raymundo; OIST</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>To make things more complicated, all of these processes – species-turnover, genetic adaptation and acclimatisation – can also occur in the microalgae communities living within each coral. Scientists like me will need to disentangle the mechanisms that have driven potential shifts in thermal tolerance in Palau and elsewhere.</p>
<h2>What does the future hold?</h2>
<p>Can coral thermal tolerance continue increasing into the future? If so, then will it be fast enough to keep pace with ocean warming? Our study tackles these questions using high-resolution future temperature projections from 17 <a href="https://www.carbonbrief.org/qa-how-do-climate-models-work/">global climate models</a>.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/543593/original/file-20230821-25-dna4wg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="three graphs" src="https://images.theconversation.com/files/543593/original/file-20230821-25-dna4wg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/543593/original/file-20230821-25-dna4wg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=750&fit=crop&dpr=1 600w, https://images.theconversation.com/files/543593/original/file-20230821-25-dna4wg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=750&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/543593/original/file-20230821-25-dna4wg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=750&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/543593/original/file-20230821-25-dna4wg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=942&fit=crop&dpr=1 754w, https://images.theconversation.com/files/543593/original/file-20230821-25-dna4wg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=942&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/543593/original/file-20230821-25-dna4wg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=942&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Projections of coral bleaching in Palau: if the Paris Agreement is achieved, in a middle-of-the-road scenario, and a worst-case scenario. An increase in thermal tolerance (blue line) buys some time, but coral reefs will still struggle unless climate change is halted.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1038/s41467-023-40601-6">Lachs et al</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Our analysis reaffirms the scientific consensus, that ultimately the future of coral reefs depends on rapidly reducing carbon emissions. However, if coral thermal tolerance can continue rising, then bleaching could be avoided on some reefs, or at least delayed. </p>
<p><a href="https://doi.org/10.1038/s41467-023-40601-6">Our study</a> and <a href="https://doi.org/10.1029/2021GL094128">others</a> have identified reefs with some level of innate climate resilience. This might buy us some time, but securing a future for coral reefs still hinges on rapid climate action. As our oceans get hotter, fewer reefs will escape bleaching conditions. </p>
<p>There are promising conservation measures, restoration efforts and more experimental interventions such as <a href="https://theconversation.com/coral-meet-coral-how-selective-breeding-may-help-the-worlds-reefs-survive-ocean-heating-166412">selective breeding</a> to increase thermal tolerance. All of these might <a href="https://www.sciencedirect.com/science/article/pii/S0006320721001592">help corals persist into the future</a>, but reducing carbon emissions is ultimately the only sure bet.</p>
<hr>
<figure class="align-right ">
<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
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<p class="fine-print"><em><span>Liam Lachs receives funding from the Natural Environment Research Council's ONE Planet Doctoral Training Programme. </span></em></p>This may buy us time, but many reefs are still doomed without serious action on climate change.Liam Lachs, PhD Candidate in Climate Change Ecology and Evolution, Newcastle UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2109742023-08-09T12:32:33Z2023-08-09T12:32:33ZThe heroic effort to save Florida’s coral reef from extreme ocean heat as corals bleach across the Caribbean<figure><img src="https://images.theconversation.com/files/541348/original/file-20230806-200746-p7nvgb.jpg?ixlib=rb-1.1.0&rect=0%2C17%2C828%2C580&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Elkhorn coral fragments rescued from overheating ocean nurseries sit in cooler water at Keys Marine Laboratory.</span> <span class="attribution"><a class="source" href="https://www.climate.gov/news-features/event-tracker/noaa-and-partners-race-rescue-remaining-florida-corals-historic-ocean">NOAA</a></span></figcaption></figure><p>Armed with scrub brushes, <a href="https://divingwithapurpose.org/">young scuba divers</a> took to the waters of Florida’s Alligator Reef in late July to try to help corals struggling to survive 2023’s extraordinary marine heat wave. They carefully scraped away harmful algae and predators impinging on staghorn fragments, under the supervision and training of interns from <a href="https://icareaboutcoral.org">Islamorada Conservation and Restoration Education</a>, or I.CARE.</p>
<p>Normally, I.CARE’s volunteer divers would be transplanting corals to waters off the Florida Keys this time of year, as part of a <a href="https://www.fisheries.noaa.gov/southeast/habitat-conservation/restoring-seven-iconic-reefs-mission-recover-coral-reefs-florida-keys">national effort to restore the Florida Reef</a>. But this year, everything is going in reverse.</p>
<p>As water temperatures spiked in the Florida Keys, scientists from universities, coral reef restoration groups and government agencies launched <a href="https://www.pbs.org/newshour/show/coral-reefs-off-coast-of-florida-bleached-as-water-temperatures-top-100-degrees-fahrenheit">a heroic effort</a> to save the corals. Divers have been in the water every day, <a href="https://www.pbs.org/newshour/show/coral-reefs-off-coast-of-florida-bleached-as-water-temperatures-top-100-degrees-fahrenheit?fbclid=IwAR1fhi0rBA2WrtlmBNFgAK5cIHqOcQDBo3dSUx_RS1XOFUvHoBHFoYwee7E">collecting thousands of corals</a> from ocean nurseries along the Florida Keys reef tract and moving them to cooler water and into giant tanks on land. </p>
<p>Marine scientist Ken Nedimyer and his team at <a href="https://reefrenewalusa.org/">Reef Renewal USA</a> moved an entire <a href="https://www.semanticscholar.org/paper/Coral-tree-nursery%C2%A9%3A-an-innovative-approach-to-in-Nedimyer-Gaines/02e1e8a6253b9a894edf92cf3131e0aaf56bc02c">coral tree nursery</a> from shallow waters off Tavernier to an area 60 feet deep and <a href="https://www.nytimes.com/2023/07/31/climate/coral-reefs-heat-florida-ocean-temperatures.html">2 degrees Fahrenheit (1.1 Celsius) cooler</a>. Even there, temperatures were running about 85 to 86 F (30 C). </p>
<figure class="align-center ">
<img alt="A diver with a collection bag retrieves corals from a stand underwater." src="https://images.theconversation.com/files/541398/original/file-20230807-20-ec3q71.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541398/original/file-20230807-20-ec3q71.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=768&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541398/original/file-20230807-20-ec3q71.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=768&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541398/original/file-20230807-20-ec3q71.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=768&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541398/original/file-20230807-20-ec3q71.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=965&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541398/original/file-20230807-20-ec3q71.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=965&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541398/original/file-20230807-20-ec3q71.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=965&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Marine scientist Ken Nedimyer collects still-healthy elkhorn coral fragments for moving. The tree structure keeps the corals free of harmful algae.</span>
<span class="attribution"><a class="source" href="https://reefrenewalusa.org/beat-the-heat/">Reef Renewal USA</a></span>
</figcaption>
</figure>
<p>Their efforts are part of an emergency response on a scale never before seen in Florida.</p>
<p>The <a href="https://floridascoralreef.org/">Florida Reef</a> – a nearly 350-mile arc along the Florida Keys that is crucial to fish habitat, coastal storm protection and <a href="https://sanctuaries.noaa.gov/science/socioeconomic/factsheets/floridakeys.html">the local economy</a> – began experiencing <a href="https://www.climate.gov/news-features/event-tracker/noaa-and-partners-race-rescue-remaining-florida-corals-historic-ocean">record-hot ocean temperatures</a> in June 2023, weeks earlier than expected. The continuing heat has triggered <a href="https://www.aoml.noaa.gov/cheeca-rocks-reef-completely-bleached/">widespread coral bleaching</a> off Florida in particular, but also beyond.</p>
<p>By mid-August, coral bleaching <a href="https://research.noaa.gov/wp-content/uploads/2023/08/NOAA-Deep-Dive-Coral-Briefing.pptx-5.pdf%22%22">had been reported</a> in the Bahamas, Cuba, Mexico, Belize, El Salvador, Costa Rica, Panama and Colombia, as well as Puerto Rico and the U.S. Virgin Islands. This is particularly devastating because some of the healthiest remaining coral reefs are in the <a href="https://www.iucn.org/sites/default/files/import/downloads/caribbean_coral_reefs___status_report_1970_2012.pdf">southern Caribbean</a>. Scientists worry they may be seeing the sixth mass bleaching of Caribbean corals since 1995 and the <a href="https://www.agrra.org/coral-bleaching">third within the past 12 years</a>, and the heat is <a href="https://www.epa.gov/climate-indicators/climate-change-indicators-sea-surface-temperature">likely to continue</a>.</p>
<figure class="align-center ">
<img alt="A white coral mound with groves and a tag on the side." src="https://images.theconversation.com/files/541480/original/file-20230807-6265-nodvp1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541480/original/file-20230807-6265-nodvp1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541480/original/file-20230807-6265-nodvp1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541480/original/file-20230807-6265-nodvp1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541480/original/file-20230807-6265-nodvp1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541480/original/file-20230807-6265-nodvp1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541480/original/file-20230807-6265-nodvp1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A bleached mound of coral at the Cheeca Rocks monitoring site in the Florida Keys National Marine Sanctuary that had been previously tagged shows the coral skeleton.</span>
<span class="attribution"><a class="source" href="https://www.aoml.noaa.gov/cheeca-rocks-reef-completely-bleached/">NOAA AOML</a></span>
</figcaption>
</figure>
<p>While corals can recover from mass bleaching events, long periods of high heat can leave them weak and vulnerable to disease that can <a href="https://www.surfrider.org/news/soaring-ocean-temperatures-trigger-coral-bleaching-event-in-south-florida">ultimately kill them</a>.</p>
<p>That’s what scientists and volunteers have been scrambling to avoid. </p>
<h2>The heartbeat of the reef</h2>
<p>The Florida Reef has struggled for years under the pressure of overfishing, disease, storms and global warming that have decimated its live corals. </p>
<p>A massive <a href="https://www.fisheries.noaa.gov/southeast/habitat-conservation/restoring-seven-iconic-reefs-mission-recover-coral-reefs-florida-keys">coral restoration effort</a> – the National Oceanic and Atmospheric Administration’s Mission: Iconic Reef – has been underway since 2019 to restore the reef with transplanted corals, particularly those most resilient to the rising temperatures. But even the hardiest coral transplants are now at risk.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/PDJXgxHs7Ak?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Divers involved in NOAA’s Mission: Iconic Reef show how staghorn and elkhorn corals are being transplanted to help the Florida Reef recover.</span></figcaption>
</figure>
<p>Reef-building corals are the foundation species of shallow tropical waters due to their unique symbiotic relationship with microscopic algae in their tissues.</p>
<p>During the day, these algae photosynthesize, producing both food and oxygen for the coral animal. At night, coral polyps feed on plankton, providing nutrients for their algae. The result of this symbiotic relationship is the coral’s ability to build a calcium carbonate skeleton and reefs that <a href="https://www.fisheries.noaa.gov/corals#overview">support nearly 25% of all marine life</a>.</p>
<p>Unfortunately, corals are very temperature sensitive, and the extreme ocean heat off South Florida, with <a href="https://www.miamiherald.com/news/local/environment/climate-change/article277828813.html">some reef areas reaching temperatures in the 90s,</a> has put them under extraordinary stress.</p>
<figure class="align-center ">
<img alt="Two images show a colorful coral with fish swimming over it and the same coral bleached, looking ghostly white." src="https://images.theconversation.com/files/541343/original/file-20230806-225752-p7nvgb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541343/original/file-20230806-225752-p7nvgb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541343/original/file-20230806-225752-p7nvgb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541343/original/file-20230806-225752-p7nvgb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541343/original/file-20230806-225752-p7nvgb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541343/original/file-20230806-225752-p7nvgb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541343/original/file-20230806-225752-p7nvgb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A boulder brain coral, <em>Colpophyllia natans</em>, before and after bleaching during the 2014 marine heat wave in the Florida Keys.</span>
<span class="attribution"><span class="source">Photos by Michael Childress and Kylie Smith</span></span>
</figcaption>
</figure>
<p>When corals get too hot, they expel their symbiotic algae. The corals appear white – bleached – because their carbonate skeleton shows through their clear tissue that lack any colorful algal cells.</p>
<p>Corals <a href="https://oceanservice.noaa.gov/facts/coral_bleach.html">can recover</a> new algal symbionts if water conditions return to normal within a few weeks. However, the increase in global temperatures due to the effects of greenhouse gas emissions from human activities is causing <a href="https://doi.org/10.1038/nature22901">longer and more frequent</a> periods of coral bleaching worldwide, leading to <a href="https://www.hawaii.edu/news/2022/10/11/coral-reefs-climate-change-threat/">concerns for the future</a> of coral reefs.</p>
<h2>A MASH unit for corals</h2>
<p>This year, the Florida Keys reached an alert level 2, indicating extreme risk of bleaching, about six weeks earlier than normal.</p>
<p>The early warnings and forecasts from <a href="https://coralreef.noaa.gov/">NOAA</a>’s <a href="https://coralreefwatch.noaa.gov/">Coral Reef Watch Network</a> gave scientists time to begin preparing labs and equipment, track the locations and intensity of the growing marine heat and, importantly, recruit volunteers.</p>
<figure class="align-center ">
<img alt="Two charts show ocean temperatures far above normal." src="https://images.theconversation.com/files/544101/original/file-20230822-28-k0267g.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/544101/original/file-20230822-28-k0267g.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/544101/original/file-20230822-28-k0267g.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/544101/original/file-20230822-28-k0267g.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/544101/original/file-20230822-28-k0267g.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/544101/original/file-20230822-28-k0267g.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/544101/original/file-20230822-28-k0267g.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This year’s maximum sea surface temperature (top chart, black bar) and degree heating weeks (lower chart, black bar), a measure of accumulated heat stress, have been the highest since record-keeping began.</span>
<span class="attribution"><a class="source" href="https://coralreefwatch.noaa.gov/data/vs/ts_figures/ts_multi_year/vs_ts_multiyr_florida_keys.png">NOAA</a></span>
</figcaption>
</figure>
<p>At the <a href="https://www.fio.usf.edu/keys-marine-lab/">Keys Marine Laboratory</a>, scientists and trained volunteers have dropped off thousands of coral fragments collected from heat-threatened offshore nurseries. Director Cindy Lewis described the lab’s giant tanks as looking like “a <a href="https://en.wikipedia.org/wiki/Mobile_Army_Surgical_Hospital">MASH unit</a> for corals.”</p>
<p>Volunteers there and at other labs across Florida will hand-feed the tiny creatures to keep them alive until the Florida waters cool again and they can be returned to the ocean and eventually transplanted onto the reef.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/543388/original/file-20230818-19-i65j2j.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A map shows high heat off Florida and the Bahamas, as well as in the tropical Pacific along the equator, where warm water indicates El Nino conditions." src="https://images.theconversation.com/files/543388/original/file-20230818-19-i65j2j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/543388/original/file-20230818-19-i65j2j.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=505&fit=crop&dpr=1 600w, https://images.theconversation.com/files/543388/original/file-20230818-19-i65j2j.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=505&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/543388/original/file-20230818-19-i65j2j.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=505&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/543388/original/file-20230818-19-i65j2j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=634&fit=crop&dpr=1 754w, https://images.theconversation.com/files/543388/original/file-20230818-19-i65j2j.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=634&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/543388/original/file-20230818-19-i65j2j.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=634&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Degree heating weeks is a measure of accumulated heat stress over the previous 12 weeks. At 4-degree Celsius-weeks (7.2 Fahrenheit-weeks), coral bleaching is expected. Above 8 C-weeks (14.4 F-weeks), significant bleaching and mortality are expected to begin.</span>
<span class="attribution"><a class="source" href="https://coralreefwatch.noaa.gov/product/5km/index_5km_dhw.php">NOAA Coral Reef Watch</a></span>
</figcaption>
</figure>
<h2>Protecting corals still in the ocean</h2>
<p><a href="https://icareaboutcoral.org">I.CARE</a> launched another type of emergency response. </p>
<p>I.CARE co-founder Kylie Smith, a coral reef ecologist and a former student of mine in marine sciences, discovered a few years ago that coral transplants with large amounts of fleshy algae around them were <a href="https://doi.org/10.1007/s00338-019-01823-7">more likely to bleach</a> during times of elevated temperature. Removing that algae may give corals a better chance of survival.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/541347/original/file-20230806-213730-ugyy8l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two photos show young people being trained to work with coral fragments and then on a dive clearing algae from around corals." src="https://images.theconversation.com/files/541347/original/file-20230806-213730-ugyy8l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541347/original/file-20230806-213730-ugyy8l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=299&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541347/original/file-20230806-213730-ugyy8l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=299&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541347/original/file-20230806-213730-ugyy8l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=299&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541347/original/file-20230806-213730-ugyy8l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=375&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541347/original/file-20230806-213730-ugyy8l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=375&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541347/original/file-20230806-213730-ugyy8l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=375&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Youth members of Diving With a Purpose attend a training session and coral maintenance dive with the Islamorada Conservation and Restoration Education team in Islamorada, Fla.</span>
<span class="attribution"><span class="source">I.CARE</span></span>
</figcaption>
</figure>
<p>Smith’s group typically works with local dive operators to train recreational divers to assist in transplanting and maintaining coral fragments in an effort to restore the reefs of Islamorada. In summer 2023, I.CARE has been training volunteers, like the young divers from <a href="https://divingwithapurpose.org/">Diving with a Purpose</a>, to remove algae and coral predators, such as <a href="https://www.marinespecies.org/aphia.php?p=taxdetails&id=419934">coral-eating snails</a> and <a href="https://www.marinebio.org/species/bearded-fireworms/hermodice-carunculata">fireworms</a>, to help boost the corals’ chances of survival.</p>
<h2>Monitoring for corals at risk</h2>
<p>To help spot corals in trouble, volunteer divers are also being trained as reef observers through Mote Marine Lab’s <a href="https://mote.org/research/program/coral-reef-science-monitoring/bleachwatch">BleachWatch</a> program.</p>
<p>Scuba divers have long been attracted to the reefs of the Florida Keys for their beauty and accessibility. The lab is training them to recognize bleached, diseased and dead corals of different species and then use an online portal to submit bleach reports across the entire Florida Reef. </p>
<p>The more eyes on the reef, the more accurate the maps showing the areas of greatest bleaching concern.</p>
<figure class="align-center ">
<img alt="A diver looks at a mounds of bleached corals" src="https://images.theconversation.com/files/541346/original/file-20230806-96278-k8vdyv.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541346/original/file-20230806-96278-k8vdyv.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541346/original/file-20230806-96278-k8vdyv.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541346/original/file-20230806-96278-k8vdyv.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541346/original/file-20230806-96278-k8vdyv.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541346/original/file-20230806-96278-k8vdyv.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541346/original/file-20230806-96278-k8vdyv.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Ian Enochs, a research ecologist and lead of NOAA’s Atlantic Oceanographic and Meteorological Lab Coral Program, found that every coral in the Cheeca Rocks area had bleached by Aug. 1, 2023.</span>
<span class="attribution"><a class="source" href="https://www.aoml.noaa.gov/cheeca-rocks-reef-completely-bleached/">NOAA AOML</a></span>
</figcaption>
</figure>
<h2>Rebuilding the reef</h2>
<p>While the marine heat wave in the Keys will inevitably kill some corals, many more will survive.</p>
<p>Through <a href="https://link.springer.com/article/10.1007/s00338-020-01948-0">careful analysis</a> of the species, genotypes and reef locations experiencing bleaching, scientists and practitioners are learning valuable information as they work to protect and rebuild a more resilient coral reef for the future.</p>
<p>That is what gives hope to Smith, Lewis, Nedimyer and hundreds of others who believe this coral reef is worth saving. Volunteers are crucial to the effort, whether they’re helping with coral reef maintenance, reporting bleaching or raising the awareness of what is at stake if humanity fails to stop warming the planet.</p>
<p><em>This article was updated Aug. 22, 2023, to correct the description of the impact of degree-heating weeks accompanying two charts. At 4-degree Celsius-weeks, coral bleaching is expected. Above 8 C-weeks, signficant bleaching and mortality are expected.</em></p><img src="https://counter.theconversation.com/content/210974/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael Childress does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Ocean temperatures have hit record highs off the Florida Keys. Scientists and volunteer divers are racing to save these valuable creatures.Michael Childress, Associate Professor of Biological Sciences & Environmental Conservation, Clemson UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2097702023-07-14T12:49:06Z2023-07-14T12:49:06ZCorals are starting to bleach as global ocean temperatures hit record highs<figure><img src="https://images.theconversation.com/files/537483/original/file-20230714-23-yzqhp8.png?ixlib=rb-1.1.0&rect=0%2C23%2C5176%2C3422&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Mass coral bleaching in 2014 left the Coral Reef Monitoring Program monitoring site at Cheeca Rocks off the Florida Keys a blanket of white.</span> <span class="attribution"><a class="source" href="https://www.aoml.noaa.gov/coral-bleaching-cheeca-rocks/">NOAA</a></span></figcaption></figure><p>The water off South Florida is <a href="https://coralreefwatch.noaa.gov/data/vs/ts_figures/ts_multi_year/vs_ts_multiyr_florida_keys.png">over 90 degrees Fahrenheit</a> (32 Celsius) in mid-July, and scientists are already seeing signs of coral bleaching off Central and South America. Particularly concerning is how early in the summer we are seeing these high ocean temperatures. If the <a href="https://theconversation.com/ocean-heat-is-off-the-charts-heres-what-that-means-for-humans-and-ecosystems-around-the-world-207902">extreme heat</a> persists, it could have dire consequences for coral reefs.</p>
<p>Just like humans, corals can handle some degree of stress, but the longer it lasts, the more harm it can do. Corals can’t move to cooler areas when water temperatures rise to dangerous levels. They are stuck in it. For those that are <a href="https://doi.org/10.1007/s00338-022-02232-z">particularly sensitive to temperature stress</a>, that can be devastating.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two photos shows a coral on two different dates, one healthy and reddish in color, the other white." src="https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=246&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=246&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=246&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=310&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=310&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=310&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A transplanted coral in the Port of Miami that was healthy in early 2023 had bleached in the warm water by July 11, 2023.</span>
<span class="attribution"><span class="source">NOAA/University of Miami</span></span>
</figcaption>
</figure>
<p><a href="https://scholar.google.com/citations?user=WS4sEzgAAAAJ&hl=en">I lead</a> the <a href="https://www.aoml.noaa.gov/coral-reef-ecosystems/">Coral Program</a> at the National Oceanic and Atmospheric Administration’s Atlantic Oceanographic and Meteorological Lab in Miami, Florida. Healthy coral reef ecosystems are important for humans in numerous ways. Unfortunately, <a href="https://theconversation.com/el-nino-is-coming-and-ocean-temps-are-already-at-record-highs-that-can-spell-disaster-for-fish-and-corals-202424">marine heat waves are becoming more common</a> and more extreme, with potentially devastating consequences for reefs around the world that are already in a fragile state.</p>
<h2>Why coral reefs matter to everyone</h2>
<p>Coral reefs are hot spots of biodiversity. They are often referred to as the <a href="https://oceanexplorer.noaa.gov/okeanos/explorations/10index/background/biodiversity/biodiversity.html">rainforests of the sea</a> because they are home to the highest concentrations of species in the ocean.</p>
<p>Healthy reefs are vibrant ecosystems that support fish and fisheries, which in turn <a href="https://www.noaa.gov/education/resource-collections/marine-life/coral-reef-ecosystems#">support economies and food for millions of people</a>. Additionally, they provide billions of dollars in economic activity every year through tourism, particularly in places like the Florida Keys, where people go to scuba dive, snorkel, fish and experience the natural beauty of coral reefs.</p>
<p>If that isn’t enough, <a href="https://www.usgs.gov/centers/pcmsc/science/role-reefs-coastal-protection">reefs also protect shorelines</a>, beaches and billions of dollars in coastal infrastructure by buffering wave energy, particularly during storms and hurricanes. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/IEWJAEkGeNk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">What goes into a coral reef?</span></figcaption>
</figure>
<p>But corals are quite <a href="https://scied.ucar.edu/learning-zone/climate-change-impacts/corals-and-climate">sensitive to warming water</a>. They host a microscopic symbiotic <a href="https://oceanservice.noaa.gov/education/tutorial_corals/coral02_zooxanthellae.html">algae called zooxanthella</a> that photosynthesizes just like plants, providing food to the coral. When the surrounding waters get too warm for too long, the zooxanthellae leave the coral, and the coral can turn pale or white – a process known as bleaching.</p>
<p>If corals stay bleached, they can become energetically compromised and ultimately die.</p>
<p>When corals die or their growth slows, these beautiful, complex reef habitats start disappearing and can eventually erode to sand. A recent paper by <a href="https://www.aoml.noaa.gov/tag/john-morris/">John Morris</a>, a scientist in my lab in Florida, shows that around <a href="https://doi.org/10.1038/s41598-022-23394-4">70% of reefs are now net erosional in the Florida Keys</a>, meaning they are losing more habitat than they build.</p>
<figure class="align-center ">
<img alt="Two maps show large areas of above average heat, particularly along the equator in the Pacific, which is an indicator of El Nino, and in much of the Atlantic." src="https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=670&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=670&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=670&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=842&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=842&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=842&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">About 40% of the global ocean was experiencing a marine heat wave in July 2023. NOAA’s experimental forecasts for August and October show sea surface temperatures well above average in many regions. An increase of 1 degree Celsius = 1.8 degrees Fahrenheit.</span>
<span class="attribution"><a class="source" href="https://psl.noaa.gov/marine-heatwaves/#report">NOAA PSL</a></span>
</figcaption>
</figure>
<p>Unfortunately, these critical coral reef habitats are in decline around the world because of extreme bleaching events, disease and numerous other human-caused stressors. In the Florida Keys, coral cover has decline by about <a href="https://www.climate.gov/news-features/features/mission-iconic-reefs-noaa-aims-restore-florida-keys-climate-resilient-corals">90% over the past several decades</a>.</p>
<h2>Coral bleaching in 2023</h2>
<p>In the Port of Miami, where we have found <a href="https://doi.org/10.1038/s41598-023-33467-7">particularly resilient coral communities</a>, a doctoral candidate in my lab, <a href="https://www.researchgate.net/profile/Allyson-Demerlis">Allyson DeMerlis</a>, documented the first coral bleaching of her experimentally <a href="https://reefresilience.org/management-strategies/restoration/coral-populations/coral-gardening/outplanting/">outplanted corals</a> on July 11, 2023.</p>
<p>Other scientists we work with have reported coral bleaching off of Colombia, El Salvador, Costa Rica and Mexico in the eastern Pacific, as well as along the Caribbean coasts of Panama, Mexico and Belize.</p>
<p>We have yet to see widespread coral death associated with this particular marine heat wave, so it is possible the corals could recover if sea surface temperatures cool down soon. However, global sea surface <a href="https://theconversation.com/ocean-heat-is-off-the-charts-heres-what-that-means-for-humans-and-ecosystems-around-the-world-207902">temperatures are at record highs</a>, and large parts of the Atlantic and eastern Pacific are <a href="https://coralreefwatch.noaa.gov/satellite/bleachingoutlook_cfs/index.php">under bleaching alerts</a>. At this point, the evidence points to the potential for a very negative outcome.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A chart of every year's global daily average sea surface temperature shows 2023 far above all other years since satellite records started in 1981." src="https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=382&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=382&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=382&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=480&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=480&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=480&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sea surface temperatures have been off the charts. The thick black line is 2023. The orange line is 2022. The 1982-2011 average is the middle dashed line.</span>
<span class="attribution"><a class="source" href="https://climatereanalyzer.org/clim/sst_daily/">ClimateReanalyzer.org/NOAA OISST v2.1</a></span>
</figcaption>
</figure>
<p><a href="https://theconversation.com/el-nino-is-back-thats-good-news-or-bad-news-depending-on-where-you-live-205974">El Niño</a> is contributing to the problem this year, but the longer-term trends of rising ocean heat are <a href="https://climate.nasa.gov/">driven by global warming</a> fueled by human activities.</p>
<p>To put that into context, <a href="https://doi.org/10.1038/srep16762">a paper</a> by NOAA scientist <a href="https://scholar.google.com/citations?user=rEv8BNoAAAAJ&hl=en">Derek Manzello</a> showed that in the Florida Keys, the number of days per year in which water temperatures were higher than 90 F (32 C) had increased by more than 2,500% in the two decades following the mid-1990s relative to the prior 20 years. That is a remarkable increase in the number of days that corals are experiencing particularly stressful warm water.</p>
<h2>What can we do to protect corals?</h2>
<p>First, we cannot give up on corals.</p>
<p><a href="https://www.aoml.noaa.gov/people/alice-webb/">Alice Webb</a>, a coral reef scientist working with our group, recently published <a href="https://doi.org/10.1038/s41598-022-26930-4">a study</a> based on years of our research in the Florida Keys. She modeled reef habitat persistence under climate, restoration and adaptation scenarios and found that protecting reefs is going to take everything – active restoration of reefs, helping corals acclimate or adapt to changing temperatures, and, importantly, human curbing of greenhouse gas emissions.</p>
<figure class="align-center ">
<img alt="A map shows warm ocean temperatures across a large part of the Atlantic and Pacific around North America." src="https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=504&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=504&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=504&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=634&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=634&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=634&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Sea surface temperatures off South Florida were abnormally high in mid-July 2023.</span>
<span class="attribution"><a class="source" href="https://coralreefwatch.noaa.gov/product/5km/index_5km_sst.php">Coral Reef Watch/NOAA</a></span>
</figcaption>
</figure>
<p>Major restoration efforts are underway in the Florida Keys as part of the NOAA-led <a href="https://marinesanctuary.org/mission-iconic-reefs/">Mission Iconic Reefs</a>. We are also assessing how different coral individuals perform under stress, hoping to identify those that are particularly stress-tolerant by combing through the massive amounts of <a href="https://www.ingentaconnect.com/contentone/umrsmas/bullmar/2023/00000099/00000002/art00006">data from restoration projects and coral nurseries</a>.</p>
<p>We are also evaluating stress-hardening techniques. For example, in tide pools, corals are exposed to large swings in temperature over short periods, making them more resilient to subsequent thermal stress events. We are exploring whether it’s possible to replicate that natural process in the lab, before corals are planted onto reefs, to better <a href="https://doi.org/10.1007/s00338-022-02232-z">prepare them for stressful summers in the wild</a>.</p>
<p>Coral bleaching on a large scale has really been documented only since the early 1980s. When I talk to people who have been fishing and diving in the Florida Keys since before I was born, they have amazing stories of how vibrant the reefs used to be. They know firsthand how bad things have become because they have lived it.</p>
<p>There isn’t currently a single silver-bullet solution, but ignoring the harm being done is not an option. There is simply too much at stake.</p><img src="https://counter.theconversation.com/content/209770/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ian Enochs receives funding from NOAA. </span></em></p>Water temperatures in the 90s off Florida in July are alarming, a NOAA coral scientist writes. Scientists in several North American countries have already spotted coral bleaching off their coasts.Ian Enochs, Research Ecologist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1977882023-02-15T16:00:14Z2023-02-15T16:00:14ZWas Earth already heating up, or did global warming reverse a long-term cooling trend?<figure><img src="https://images.theconversation.com/files/508700/original/file-20230207-21-1bdmxo.jpg?ixlib=rb-1.1.0&rect=166%2C39%2C5107%2C3328&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Natural records suggest a cooling trend was underway thousands of years ago.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/ploughing-scene-wall-painting-tomb-of-sennedjem-valley-of-news-photo/475591523">DeAgostini/Getty Images</a></span></figcaption></figure><p>Over the past century, the Earth’s average temperature has swiftly <a href="https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature">increased by about 1 degree Celsius</a> (1.8 degrees Fahrenheit). The evidence is hard to dispute. It comes from thermometers and other sensors around the world.</p>
<p>But what about the thousands of years before the Industrial Revolution, before thermometers, and before humans warmed the climate by <a href="https://climate.nasa.gov/faq/19/what-is-the-greenhouse-effect/">releasing heat-trapping carbon dioxide from fossil fuels</a>?</p>
<p>Back then, was Earth’s temperature warming or cooling?</p>
<p>Even though scientists know more about the most recent 6,000 years than any other multimillennial interval, studies on this long-term global temperature trend have come to <a href="https://doi.org/10.1073/pnas.1407229111">contrasting conclusions</a>.</p>
<p>To try to resolve the difference, we conducted a comprehensive, global-scale assessment of the existing evidence, including both natural archives, like tree rings and seafloor sediments, and climate models. Our results, <a href="https://www.nature.com/articles/s41586-022-05536-w">published Feb. 15, 2023</a>, suggest ways to improve climate forecasting to avoid missing some important slow-moving, naturally occurring climate feedbacks.</p>
<h2>Global warming in context</h2>
<p>Scientists like us who study past climate, or <a href="https://www.usgs.gov/programs/climate-research-and-development-program/science/paleoclimate-research">paleoclimate</a>, look for temperature data from far back in time, long before thermometers and satellites.</p>
<p>We have two options: We can find information about past climate stored <a href="https://interactive.carbonbrief.org/how-proxy-data-reveals-climate-of-earths-distant-past/">in natural archives</a>, or we can simulate the past using <a href="https://www.carbonbrief.org/qa-how-do-climate-models-work/">climate models</a>.</p>
<p>There are several natural archives that record changes in the climate over time. The growth rings that form each year in <a href="https://scied.ucar.edu/learning-zone/how-climate-works/tree-rings-and-climate">trees</a>, <a href="https://eos.org/editors-vox/stalagmite-layers-reveal-hidden-climate-stories">stalagmites</a> and <a href="https://www.ncei.noaa.gov/news/how-can-corals-teach-us-about-climate">corals</a> can be used to reconstruct past temperature. Similar data can be found in <a href="https://icecores.org/about-ice-cores">glacier ice</a> and in tiny shells found in the <a href="https://www.icm.csic.es/en/news/what-do-marine-sediments-tell-us-about-earths-climate">sediment that builds up over time at the bottom of the ocean</a> or <a href="https://www.earth.ox.ac.uk/2017/01/using-lake-sediments-to-understand-past-climate/">lakes</a>. These serve as substitutes, or proxies, for thermometer-based measurements.</p>
<figure class="align-center ">
<img alt="Illustration shows different types of natural archives and how cores are taken." src="https://images.theconversation.com/files/506970/original/file-20230130-508-h5lwde.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/506970/original/file-20230130-508-h5lwde.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/506970/original/file-20230130-508-h5lwde.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/506970/original/file-20230130-508-h5lwde.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/506970/original/file-20230130-508-h5lwde.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/506970/original/file-20230130-508-h5lwde.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/506970/original/file-20230130-508-h5lwde.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Trees are the best-known natural archives. Here are several others that hold evidence of past temperature. Cores or other samples from these archives can be used to reconstruct changes over time.</span>
<span class="attribution"><a class="source" href="https://www.victorleshyk.com/">Viktor O. Leshyk</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>For example, changes in the width of tree rings can <a href="https://doi.org/10.1007/s00382-012-1611-x">record temperature fluctuations</a>. If temperature during the growing season is too cold, the tree ring forming that year is thinner that one from a year with warmer temperatures.</p>
<p>Another temperature proxy is found in seafloor sediment, in the remains of tiny ocean-dwelling creatures called <a href="https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/foraminifera/">foraminifera</a>. When a foraminifer is alive, the chemical composition of its <a href="https://blogs.egu.eu/divisions/cl/2017/11/24/forams-the-sea-thermometers-of-the-past/">shell changes depending on the temperature of the ocean</a>. When it dies, the shell sinks and gets buried by other debris over time, forming layers of sediment at the ocean floor. Paleoclimatologists can then extract sediment cores and chemically analyze the shells in those layers to determine their composition and age, sometimes going back millennia.</p>
<figure class="align-center ">
<img alt="Two female scientists aboard a boat examine a sediment core, with the layers clearly visible." src="https://images.theconversation.com/files/506968/original/file-20230130-14-2uvwwp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/506968/original/file-20230130-14-2uvwwp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/506968/original/file-20230130-14-2uvwwp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/506968/original/file-20230130-14-2uvwwp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/506968/original/file-20230130-14-2uvwwp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/506968/original/file-20230130-14-2uvwwp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/506968/original/file-20230130-14-2uvwwp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Ellie Broadman, right, an author of this article, holds a sediment core from a lake on Alaska’s Kenai Peninsula.</span>
<span class="attribution"><span class="source">Emily Stone</span></span>
</figcaption>
</figure>
<p>Climate models, our other tool for exploring past environments, are mathematical representations of the Earth’s climate system. They model relationships among the atmosphere, biosphere and hydrosphere to create our best replica of reality.</p>
<p>Climate models are used to <a href="https://www.carbonbrief.org/analysis-how-well-have-climate-models-projected-global-warming/">study current conditions</a>, <a href="https://www.ipcc.ch/report/emissions-scenarios/?idp=0">forecast changes in the future</a> and <a href="https://pmip.lsce.ipsl.fr/about_us/overview">reconstruct the past</a>. For example, scientists can input the past concentrations of greenhouse gases, which we know from <a href="https://doi.org/10.1038/s43017-022-00351-3">information stored in tiny bubbles in ancient ice</a>, and the model can use that information to simulate past temperature. Modern climate data and details from natural archives are used to test their accuracy.</p>
<p>Proxy data and climate models have different strengths.</p>
<p>Proxies are tangible and measurable, and they often have a well-understood response to temperature. However, they are not evenly distributed around the world or through time. This makes it difficult to reconstruct global, continuous temperatures.</p>
<p>In contrast, climate models are continuous in space and time, but while they are often very skillful, they will never capture every detail of the climate system.</p>
<h2>A paleo-temperature conundrum</h2>
<p>In our <a href="https://www.nature.com/articles/s41586-022-05536-w">new review paper</a>, we assessed climate theory, proxy data and model simulations, focusing on indicators of global temperature. We carefully considered naturally occurring processes that affect the climate, including long-term variations in <a href="https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/">Earth’s orbit around the Sun</a>, greenhouse gas concentrations, <a href="https://scied.ucar.edu/learning-zone/how-climate-works/how-volcanoes-influence-climate">volcanic eruptions</a> and <a href="https://www.climate.gov/news-features/understanding-climate/climate-change-incoming-sunlight">the strength of the Sun’s heat energy</a>.</p>
<p>We also examined important climate feedbacks, such as vegetation and sea ice changes, that can <a href="https://scied.ucar.edu/learning-zone/how-climate-works/albedo-and-climate">influence global temperature</a>. For example, there is strong evidence that <a href="https://doi.org/10.1016/j.quascirev.2013.10.022">less Arctic sea ice</a> and <a href="https://doi.org/10.2307/2997337">more vegetation cover</a> existed during a period around 6,000 years ago than in the 19th century. That would have darkened the Earth’s surface, causing it to absorb more heat.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/507969/original/file-20230202-12383-ugtxhe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/507969/original/file-20230202-12383-ugtxhe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/507969/original/file-20230202-12383-ugtxhe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=323&fit=crop&dpr=1 600w, https://images.theconversation.com/files/507969/original/file-20230202-12383-ugtxhe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=323&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/507969/original/file-20230202-12383-ugtxhe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=323&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/507969/original/file-20230202-12383-ugtxhe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=406&fit=crop&dpr=1 754w, https://images.theconversation.com/files/507969/original/file-20230202-12383-ugtxhe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=406&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/507969/original/file-20230202-12383-ugtxhe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=406&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Some example of foraminifera shells.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Foraminifera_Phototable.jpg">From Anna Tikhonova, Sofia Merenkova, Sergei Korsun and Alexander Matul via Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Our two types of evidence offer different answers regarding the Earth’s temperature trend over the 6,000 years before modern global warming.
Natural archives generally show that Earth’s average temperature roughly 6,000 years ago was warmer by <a href="https://doi.org/10.1038/s41597-020-0530-7">about 0.7 C (1.3 F) compared with the 19th century median</a>, and then cooled gradually until the Industrial Revolution. We found that most evidence points to this result.</p>
<p>Meanwhile, climate models generally show a slight warming trend, corresponding to a gradual increase in carbon dioxide as <a href="https://education.nationalgeographic.org/resource/development-agriculture">agriculture-based societies developed</a> during the millennia after <a href="https://www.livescience.com/40311-pleistocene-epoch.html">ice sheets retreated</a> in the Northern Hemisphere.</p>
<h2>How to improve climate forecasts</h2>
<p>Our assessment highlights some ways to improve climate forecasts.</p>
<p>For example, we found that models would be more powerful if they more fully represented certain climate feedbacks. One <a href="https://doi.org/10.1126/sciadv.abj6535">climate model experiment</a> that included increased vegetation cover in some regions 6,000 years ago was able to simulate the global temperature peak we see in proxy records, unlike most other model simulations, which don’t include this expanded vegetation.</p>
<p>Understanding and better incorporating these and other feedbacks <a href="https://doi.org/10.1029/2019GL085982">will be important</a> as scientists continue to improve our ability to predict future changes.</p><img src="https://counter.theconversation.com/content/197788/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ellie Broadman has received funding from the National Science Foundation, the University of Arizona, and Northern Arizona University.</span></em></p><p class="fine-print"><em><span>Darrell Kaufman receives funding from the National Science Foundation.</span></em></p>Evidence in Earth’s natural archives, from tree rings to seafloor sediments, points to one trend. Some climate models suggest another.Ellie Broadman, Postdoctoral Research Associate in Climate Science, University of ArizonaDarrell Kaufman, Professor of Earth and Environmental Sciences, Northern Arizona UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1972152023-01-09T17:10:21Z2023-01-09T17:10:21ZInvasive rats are changing fish behaviour on coral reefs – new study<figure><img src="https://images.theconversation.com/files/503231/original/file-20230105-1808-63w6g0.jpg?ixlib=rb-1.1.0&rect=14%2C0%2C4866%2C2744&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Invasive rats can fundamentally alter the functioning of surrounding marine ecosystems.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/funny-image-three-positions-running-rat-48864871">Bluerain/Shutterstock</a></span></figcaption></figure><p>Coral reefs are degrading rapidly to the extent that their marine inhabitants must either adapt or die. For many animals, including reef fish, <a href="https://www.nature.com/articles/s41558-018-0314-7">behaviour</a> is one of the first responses to changes in environmental conditions.</p>
<p>Behavioural changes may be critical for predicting the future survival of many animal species. This is encouraging marine scientists to study how, why or when these changes happen. </p>
<p>Much of the existing research into the impact of environmental change on reef fish species tends to focus on increasing sea temperatures and ocean acidification. But some coral reef ecosystems are also threatened by one, more surprising source. An invasive species – the black rat – has overrun many islands in the <a href="https://commons.wikimedia.org/wiki/File:Chagos_map.PNG">Chagos Archipelago</a>, a remote group of small islands in the Indian Ocean. The rats are altering the functioning of surrounding marine ecosystems. </p>
<p><a href="https://www.nature.com/articles/s41559-022-01931-8">Recent research</a> that we co-authored alongside colleagues from Lakehead University in Canada revealed that these rats are affecting the territorial behaviour of fish by reducing the flow of nutrients from bird droppings into the ocean. </p>
<p>We focused on the <a href="https://seaunseen.com/jewel-damselfish/">jewel damselfish</a>, a small fish that aggressively defends patches of edible algae it cultivates through a process known as “farming”. Our research surveyed coral reefs both around islands with high seabird densities and without rats, and islands with low seabird densities and many rats. Jewel damselfish in the seas surrounding rat-infested islands were less aggressive and defended larger territories than those surrounding rat-free islands. </p>
<h2>Invasive rats</h2>
<p>The rats, many of which arrived on the Chagos Archipelago on ships in the 18th century, prey on small seabirds and their eggs. This has decimated seabird populations on these islands. Seabird densities are up to <a href="https://www.nature.com/articles/s41586-018-0202-3">760 times smaller</a> on rat-infested islands than on islands without rats. </p>
<p>But seabirds are a key component of the nutrient cycle. They feed in the ocean and return to the islands to roost and breed where they deposit large quantities of droppings. Their droppings, which are rich in nutrients, are then washed into the sea and onto nearby coral reefs. </p>
<p>By supplementing coral reefs with additional natural nutrients, seabirds are able to fertilise these ecosystems. Rat predation has disrupted this cycle and removed the nutrients provided by seabirds to coral ecosystems. </p>
<figure class="align-center ">
<img alt="A bird in flight against the backdrop of the ocean." src="https://images.theconversation.com/files/503224/original/file-20230105-18-vbjshz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/503224/original/file-20230105-18-vbjshz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/503224/original/file-20230105-18-vbjshz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/503224/original/file-20230105-18-vbjshz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/503224/original/file-20230105-18-vbjshz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/503224/original/file-20230105-18-vbjshz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/503224/original/file-20230105-18-vbjshz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Brown booby, a seabird species found in the Chagos.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/full-stretch-flight-juvenile-brown-bobby-1311357596">sushil20087817/Shutterstock</a></span>
</figcaption>
</figure>
<h2>Aggressive economics</h2>
<p>We found that algae in jewel damselfish territories next to rat-free islands were richer in nutrients than in territories next to rat-infested islands. However, the total amount of algae within the territories was unaffected. </p>
<p>This means that the quality, but not the quantity, of the food resources available to the jewel damselfish is higher in the waters surrounding rat-free islands. The fish in these territories get “more for their money” when foraging. The quality of nutrients means that fish are able to find all the food they need in smaller territories than fish around rat-infested islands. </p>
<p>But this carries behavioural consequences. We found that jewel damselfish in reefs surrounding rat-free islands were five times more likely to be more aggressive and 70 times more likely to hold smaller territories than those next to rat-infested islands.</p>
<p>The additional nutrients from seabird droppings in seas around islands with large seabird populations raise the quality of jewel damselfish territories and make them worth defending. The quality of nutrients in these locations means that the nutritional benefits of defending a territory are higher than the energy costs expended by aggressively defending them. </p>
<p>This is not the case for jewel damselfish in seas around rat-infested islands. The disruption to the nutrient cycle here results in lower quality territories that are less worth defending. </p>
<h2>Small fish, big impact</h2>
<p>By disrupting the nutrient cycle, invasive rats have directly reduced the aggressive tendencies of damselfish. But this behavioural change may alter the wider coral ecosystem. </p>
<p>The social organisation of <a href="https://www.nationalgeographic.com/animals/fish/facts/blue-tang">blue tangs</a>, a fish native to coral reefs in the Indo-Pacific, can be influenced by the territoriality of farming damselfish. Tangs tend to form schools in areas of the reef with high densities of territorial damselfish. This is likely because it allows “safety in numbers” when accessing defended algae and increases competition for algal food resources. But <a href="https://doi.org/10.1007/s10641-004-2861-1">research</a> has found that where damselfish densities are low, tangs rarely form schools. </p>
<figure class="align-center ">
<img alt="A school of blue fish swimming through a coral reef." src="https://images.theconversation.com/files/503247/original/file-20230105-18-yexznc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/503247/original/file-20230105-18-yexznc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/503247/original/file-20230105-18-yexznc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/503247/original/file-20230105-18-yexznc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/503247/original/file-20230105-18-yexznc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/503247/original/file-20230105-18-yexznc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/503247/original/file-20230105-18-yexznc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Invasive rats may indirectly affect the social organisation of some species.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/school-blue-tang-136660415">Isabelle Kuehn/Shutterstock</a></span>
</figcaption>
</figure>
<p>Algal productivity (grams of biomass per square metre) can also be affected by territorial damselfish. Algae within farming damselfish territories can, for example, be <a href="https://www.int-res.com/articles/meps/40/m040p041.pdf">up to 3.4 times</a> more productive than algae growing outside of the territories.</p>
<p>Territorial damselfish can also impact the density of coral within an area and therefore the structure of a reef. In Kenya, <a href="https://doi.org/10.1007/s00338-014-1229-z">research</a> has shown that the density of juvenile coral is lower inside farming damselfish territories than that in non-defended areas. Invasive rats may therefore affect coral replenishment and the functioning of the wider ecosystem.</p>
<p>By establishing the link between fish behaviour and the seabird nutrient cycle, our study highlights the potential for rat eradication to restore territorial fish behaviour. Measures to eradicate invasive rats from tropical islands have slowly been introduced across the Indian Ocean over the past 16 years. <a href="https://doi.org/10.1016/j.cub.2021.03.104">Evidence</a> suggests that these measures have contributed to the return of seabird nutrients to tropical islands and coral reefs. </p>
<p>Animal behaviour is an important but understudied aspect of biological research into ecological responses to environmental change and should be a focal point for future studies.</p><img src="https://counter.theconversation.com/content/197215/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sally Keith receives funding from NERC. </span></em></p><p class="fine-print"><em><span>This research was supported by the Natural Environment Research Council (Rachel L. Gunn, grant number NE/L002604/1), with Rachel L. Gunns studentship through the Envision Doctoral Training Partnership.</span></em></p>Rats are disrupting the flow of nutrients towards the sea on many tropical islands – this has consequences for fish behaviour and the wider ecosystem.Sally Keith, Senior Lecturer, Lancaster UniversityRachel Gunn, Postdoctoral researcher in the Animal Evolutionary Ecology, University of TübingenLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1951122022-11-23T13:19:32Z2022-11-23T13:19:32ZScientists discover five new species of black corals living thousands of feet below the ocean surface near the Great Barrier Reef<figure><img src="https://images.theconversation.com/files/496848/original/file-20221122-17-4lu9z6.jpg?ixlib=rb-1.1.0&rect=10%2C15%2C3375%2C1888&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Researchers discovered five new species of black corals, including this *Hexapathes bikofskii* growing out of a nautilus shell more than 2,500 feet (760 meters) below the surface.</span> <span class="attribution"><span class="source">Jeremy Horowitz</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p><em>The <a href="https://theconversation.com/us/topics/research-brief-83231">Research Brief</a> is a short take about interesting academic work.</em> </p>
<h2>The big idea</h2>
<p>Using a remote-controlled submarine, my colleagues <a href="https://scholar.google.com/citations?user=inNswpIAAAAJ&hl=en&oi=sra">and I</a> <a href="https://doi.org/10.11646/zootaxa.5213.1.1">discovered five new species of black corals</a> living as deep as 2,500 feet (760 meters) below the surface in the Great Barrier Reef and Coral Sea off the coast of Australia.</p>
<p>Black corals can be found growing both in <a href="https://doi.org/10.11646/zootaxa.4821.3.7">shallow waters and down to depths of over 26,000 feet</a> (8,000 meters), and some individual corals <a href="https://ocean.si.edu/ocean-life/invertebrates/how-old-black-coral">can live for over 4,000 years</a>. Many of these corals are branched and look like <a href="http://dx.doi.org/10.1016/B978-0-12-394282-1.00002-8">feathers, fans or bushes, while others are straight</a> like a whip. Unlike their colorful, shallow-water cousins that rely on the sun and photosynthesis for energy, black corals are <a href="http://dx.doi.org/10.1016/B978-0-12-394282-1.00002-8">filter feeders and eat tiny zooplankton</a> that are abundant in deep waters.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/MYncyEIDr10?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The team of researchers collected 60 specimens of black corals over 31 dives using a remotely operated submarine.</span></figcaption>
</figure>
<p>In 2019 and 2020, I and a team of Australian scientists used the <a href="https://schmidtocean.org/">Schmidt Ocean Institute’s</a> remotely operated vehicle – a submarine named SuBastian – to explore the Great Barrier Reef and Coral Sea. Our goal was to collect samples of coral species living in waters from 130 feet to 6,000 feet (40 meters to 1,800 meters) deep. In the past, corals from the deep parts of this region were collected <a href="https://doi.org/10.11646/zootaxa.4472.2.5">using dredging and trawling</a> methods that would often destroy the corals. </p>
<p>Our two expeditions were the first to send a robot down to these particular deep-water ecosystems, allowing our team to actually see and safely collect deep sea corals in their natural habitats. Over the course of 31 dives, my colleagues and I collected 60 black coral specimens. We would carefully remove the corals from the sandy floor or coral wall using the rover’s robotic claws, place the corals in a pressurized, temperature-controlled storage box and then bring them up to the surface. We would then examine the physical features of the corals and sequence their DNA. </p>
<p>Among the many interesting specimens were five new species – including one we found growing on the shell of a nautilus more than <a href="https://doi.org/10.11646/zootaxa.5213.1.1">2,500 feet (760 meters) below the ocean’s surface</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/496843/original/file-20221122-15-lxiyuo.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A robotic arm grabbing a thin coral off of a rock." src="https://images.theconversation.com/files/496843/original/file-20221122-15-lxiyuo.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/496843/original/file-20221122-15-lxiyuo.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=541&fit=crop&dpr=1 600w, https://images.theconversation.com/files/496843/original/file-20221122-15-lxiyuo.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=541&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/496843/original/file-20221122-15-lxiyuo.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=541&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/496843/original/file-20221122-15-lxiyuo.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=680&fit=crop&dpr=1 754w, https://images.theconversation.com/files/496843/original/file-20221122-15-lxiyuo.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=680&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/496843/original/file-20221122-15-lxiyuo.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=680&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Researchers used the robotic arm of their rover to collect over 100 samples of rare corals and brought them up to the surface for further study.</span>
<span class="attribution"><span class="source">Jeremy Horowitz</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Why it matters</h2>
<p>Similarly to shallow-water corals that build colorful reefs full of fish, black corals act as important habitats where <a href="http://dx.doi.org/10.1016/B978-0-12-394282-1.00002-8">fish</a> and <a href="https://doi.org/10.26496/bjz.2019.33">invertebrates</a> feed and hide from predators in what is otherwise a mostly barren sea floor. For example, a single black coral colony researchers collected in 2005 off the coast of California was <a href="https://www.researchgate.net/publication/228350918">home to 2,554 individual invertebrates</a>.</p>
<p>Recent research has begun to paint a picture of a deep sea that contains <a href="https://doi.org/10.5670/oceanog.2020.supplement.01">far more species</a> than <a href="https://doi.org/10.3389/fmars.2021.608665">biologists previously thought</a>. Considering there are only 300 known species of black corals in the world, finding five new species in one general location was very surprising and exciting for our team. Many black corals are <a href="https://www.researchgate.net/publication/304623882_Illegal_harvesting_and_trading_of_black_corals_Antipatharia_in_Madagascar_the_necessity_of_field_studies">threatened by illegal harvesting for jewelry</a>. In order to pursue smart conservation of these fascinating and hard-to-reach habitats, it is important for researchers to know what species live at these depths and the geographic ranges of individual species. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/496830/original/file-20221122-25-tu2m7q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A large, white, tree-like coral underwater." src="https://images.theconversation.com/files/496830/original/file-20221122-25-tu2m7q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/496830/original/file-20221122-25-tu2m7q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=515&fit=crop&dpr=1 600w, https://images.theconversation.com/files/496830/original/file-20221122-25-tu2m7q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=515&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/496830/original/file-20221122-25-tu2m7q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=515&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/496830/original/file-20221122-25-tu2m7q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=647&fit=crop&dpr=1 754w, https://images.theconversation.com/files/496830/original/file-20221122-25-tu2m7q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=647&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/496830/original/file-20221122-25-tu2m7q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=647&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Black corals don’t form large reefs like shallow corals, but individuals can get quite large – like this <em>Antipathes dendrochristos</em> found off the coast of California – and act as habitat for thousands of other organisms.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/File:Antipathes_dendrochristos.jpg#/media/File:Antipathes_dendrochristos.jpg">Mark Amend/NOAA via Wikimedia Commons</a></span>
</figcaption>
</figure>
<h2>What still isn’t known</h2>
<p>Every time scientists explore the deep sea, they discover new species. Simply exploring more is the best thing researchers can do to fill in knowledge gaps about what species live there and how they are distributed.</p>
<p>Because so few specimens of deep-sea black corals have been collected, and so many undiscovered species are likely still out there, there is also a lot to learn about the evolutionary tree of corals. The more species that biologists discover, the better we will be able to understand their evolutionary history – including how they have <a href="https://doi.org/10.1038/s41559-020-01291-1">survived at least four mass extinction events</a>.</p>
<h2>What’s next</h2>
<p>The next step for my colleagues and me is to continue to explore the ocean’s seafloor. Researchers have yet to <a href="https://doi.org/10.11646/zootaxa.5213.1.1">collect DNA from most of the known species of black corals</a>. In future expeditions, my colleagues and I plan to return to other deep reefs in the Great Barrier Reef and Coral Sea to continue to learn more about and better protect these habitats.</p><img src="https://counter.theconversation.com/content/195112/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jeremy Horowitz currently works for the Smithsonian Institution.
This research was funded through the ARC DECRA (DE170100516), the ARC
Centre of Excellence Program (CE140100020), and ARC Centre of Excellence Discovery Grant DP180103199.
</span></em></p>Black corals provide critical habitat for many creatures that live in the dark, often barren, deep sea, and researchers are learning more about these rare corals with every dive.Jeremy Horowitz, Post-doctoral Fellow in Invertebrate Zoology, Smithsonian InstitutionLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1920142022-11-14T19:00:33Z2022-11-14T19:00:33ZAt least 700,000 years ago, the world’s largest sand island emerged as the barrier that helped the Great Barrier Reef form<figure><img src="https://images.theconversation.com/files/494994/original/file-20221114-15-f7r4qi.jpg?ixlib=rb-1.1.0&rect=1279%2C0%2C4749%2C3215&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Scientists had always been puzzled why the Great Barrier Reef formed long after Australia had conditions suitable for reef growth. It turns out the answer might be K'gari (Fraser Island). </p>
<p>K’gari, the world’s largest sand island and a <a href="https://whc.unesco.org/en/list/630/">UNESCO World Heritage Area</a>, juts out from the Australian coastline where the continent extends furthest east. It lies at the northern end of one of the world’s largest and longest <a href="https://www.internetgeography.net/topics/what-is-longshore-drift/">longshore drift</a> systems. If not for the presence of K’gari, the sand carried by this system would continue to migrate northward directly into the area of the Great Barrier Reef, which starts a little north of the island.</p>
<p>The volumes of sand carried along the coast are immense. It is estimated <a href="https://www.abc.net.au/news/2020-06-13/weather-longshore-drift-queensland-nsw-beaches/12347828">500,000 cubic metres of sand</a> moves north past each metre of shoreline every year. </p>
<p>K’gari plays a key role in delivering this sand to the deep ocean. Sand moving along its eastern beaches is directed across the continental shelf and into the deep immediately north of the island. The dominant south-easterly trades would drive sand all the way into the full tropics if K’gari did not direct it off the shelf.</p>
<p><a href="https://www.nature.com/articles/s41561-022-01062-6">Our research</a>, published today, has established the age of K'gari as being older than the Greater Barrier Reef. This suggests the reef became established only after the island protected it from the northward drift of sand.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/437049/original/file-20211212-170692-b3s288.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/437049/original/file-20211212-170692-b3s288.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/437049/original/file-20211212-170692-b3s288.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=672&fit=crop&dpr=1 600w, https://images.theconversation.com/files/437049/original/file-20211212-170692-b3s288.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=672&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/437049/original/file-20211212-170692-b3s288.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=672&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/437049/original/file-20211212-170692-b3s288.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=844&fit=crop&dpr=1 754w, https://images.theconversation.com/files/437049/original/file-20211212-170692-b3s288.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=844&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/437049/original/file-20211212-170692-b3s288.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=844&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The northernmost point of K’gari, Sandy Point, marks where the sand heads deeper underwater, moving along the continental shelf before dropping off the edge.</span>
<span class="attribution"><span class="source">Data: Geoscience Australia Landsat 5 and 8 Geomedian. Compilation: Will Farebrother, from Conversation article by Hanna Power</span></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/from-enormous-tides-to-millions-of-shells-here-are-6-unique-beaches-for-your-summer-road-trip-169164">From enormous tides to millions of shells, here are 6 unique beaches for your summer road trip</a>
</strong>
</em>
</p>
<hr>
<h2>Why does the reef depend on the island?</h2>
<p>The southern limit of the Great Barrier Reef is not a result of the climate being too cool further south. Corals can and do grow many hundreds of kilometres further south in places like Moreton Bay (Brisbane) and Lord Howe Island. </p>
<p>The main limiting factor for the southern extent of the reef is the drowning of corals by the rivers of sand going north. The corals in places like Moreton Bay occur where they have a hard substrate to grow on and are sheltered from sediment inundation. </p>
<p>The sand comes from sediment delivered to the Tasman Sea via the Hawkesbury and Hunter rivers in mid-New South Wales. Prevailing south-easterly breezes and their associated coastal wave systems sweep these sediments north for more than 1,000 kilometres. </p>
<p>The geological setting of eastern Australia is rather stable, so this longshore drift system should have been in operation for many millions of years. The Great Barrier Reef corals could not have survived without some protection from this northward flow of sand.</p>
<p>The <a href="https://onlinelibrary.wiley.com/doi/10.1002/esp.5387">techniques</a> we used to establish the age of the coastal dune fields of K’gari and the adjacent Cooloola Sand Mass on the mainland south of K’gari show the first coastal dunes date to about 1 million years ago. The modern dune fields were established by 700,000-800,000 years ago. Prior to 1 million years and definitely prior to 700,000-800,000 years ago, sand would have drifted north into the region of the modern barrier reef. </p>
<figure class="align-center ">
<img alt="Looking out to sea from a coastal dune" src="https://images.theconversation.com/files/494996/original/file-20221114-20-ks48az.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/494996/original/file-20221114-20-ks48az.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/494996/original/file-20221114-20-ks48az.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/494996/original/file-20221114-20-ks48az.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/494996/original/file-20221114-20-ks48az.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/494996/original/file-20221114-20-ks48az.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/494996/original/file-20221114-20-ks48az.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Dating of the Cooloola dune fields on the mainland shows the oldest dunes are about 1 million years old.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/celebrating-kgari-why-the-renaming-of-fraser-island-is-about-so-much-more-than-a-name-168378">Celebrating K’gari: why the renaming of Fraser Island is about so much more than a name</a>
</strong>
</em>
</p>
<hr>
<h2>Why did K'gari form at that time?</h2>
<p>This timing coincides with a major geo-astronomical event, the <a href="https://en.wikipedia.org/wiki/Mid-Pleistocene_Transition">Mid-Pleistocene Transition</a>. At this time Earth’s glacial cycles changed from a period of about 40,000 years to about 100,000 years. This change had a major impact on global sea levels because the longer cycles supported the growth of larger ice caps during cold periods. </p>
<p>Prior to this transition, global sea levels went up and down about 70 metres between warm (interglacial) and cold (glacial) periods. Afterwards, the range increased to 120-130m.</p>
<p>Under a longshore drift system some sediment “leaks” out into deeper water where currents and waves are not strong enough to move it. A drop of 70m would still leave the South-East Queensland coastline on the continental shelf. So, before the Mid-Pleistocene Transition, sand moving north would be gradually stored on the outer parts of the continental shelf, potentially accumulating over millions of years. </p>
<p>Once the first 100,000-year cycle occurred, sea levels would have dropped to the outer edge of the continental shelf. During the start of the next warm period, rising sea levels would erode the accumulated sands and transport it shoreward. This would drive a major period of dune building along the coast. </p>
<p>This was a major event because sediment accumulated over millions of years was added back into the sedimentary system. The very different dune types associated with plentiful sand are recorded in the oldest parts of the cliff sections at Cooloola and K’gari. </p>
<p>Again, remnants of dunes formed when sea levels were low are preserved directly off this coastline. We have shown a major pulse of sand was released into the dune systems formed during the earliest high sea-level periods of the 100,000-year climate cycles.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/climate-explained-humans-have-dealt-with-plenty-of-climate-variability-145043">Climate explained: humans have dealt with plenty of climate variability</a>
</strong>
</em>
</p>
<hr>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/494999/original/file-20221114-42960-xt8y6i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/494999/original/file-20221114-42960-xt8y6i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/494999/original/file-20221114-42960-xt8y6i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/494999/original/file-20221114-42960-xt8y6i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/494999/original/file-20221114-42960-xt8y6i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/494999/original/file-20221114-42960-xt8y6i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/494999/original/file-20221114-42960-xt8y6i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The extraordinary beauty and diversity of the Great Barrier Reef would not exist without protection from the rivers of sand flowing north along the coast.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>How does that line up with the age of the reef?</h2>
<p>K’gari was constructed in its “modern” form between about 1 million and 700,000 years ago. Once it was in place, any further sand driven up the coast during interglacial high sea levels was lost to deep water off the north of K’gari.</p>
<p>The last piece of the puzzle is the age of the Great Barrier Reef. For a heavily investigated natural wonder, this is remarkably poorly defined, but the oldest evidence dates the reef to <a href="https://doc.rero.ch/record/9147/files/spezzaferri_isc.pdf">about 650,000 years ago</a>. </p>
<p>In short, coral reef development appears to not have started until sediment drift from the south was blocked off. In this way the whole of the east coast of Australia is linked together as a single story and K’gari has played a key role in the formation and protection of the Great Barrier Reef.</p><img src="https://counter.theconversation.com/content/192014/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Shulmeister received funding for this work from the Australian Research Council. James Shulmeister has been funded from the Marsden Fund (NZ), he has also participated in US NSF and Chinese NSF grants as well as received grants from other sources.</span></em></p><p class="fine-print"><em><span>Daniel Ellerton completed his PhD which was funded by the Australian Research Council.</span></em></p>Establishing the age of K'gari (Fraser Island) confirms it emerged before the reef, despite the climate being suitable for coral growth long before then.James Shulmeister, Adjunct Professor, University of Queensland, and Professor and Head of School of Earth and Environment, University of CanterburyDaniel Ellerton, Postdoctoral Researcher, Department of Geological Sciences, Stockholm UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1801942022-03-30T18:11:55Z2022-03-30T18:11:55ZInside the Mediterranean sea’s ‘animal forests’: an encounter with the gorgonian corals<figure><img src="https://images.theconversation.com/files/454761/original/file-20220328-13-1efag0j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An underwater forest formed by the purple gorgonian (Paramuricea clavata) off Marseille at a depth of 60 metres. </span> <span class="attribution"><span class="source">Romain Bricoult / CC BY-NC-ND</span></span></figcaption></figure><p>Gorgonians are an order of soft corals that belong to the large group of Cnidaria, which also includes hard corals, sea anemones, jellyfish and many other species. Gorgonians colonise the seabed all over the world, from shallow coastal areas to deep sea canyons, temperate and tropical areas to polar zones.</p>
<p>Gorgonians’ skeleton can be soft or rigid, horny or calcareous. These organisms can form dense communities that structure the seabed, constituting “animal forests” offering a refuge to a myriad of marine species.</p>
<h2>One of the most beautiful underwater landscapes in the Mediterranean</h2>
<p>In the Mediterranean, a total of five main species of gorgonians can be found living up to 100 metres below the surface. One of them, <em>Paramuricea clavata</em>, forms remarkable populations both by its red colours and the size of its colonies, which can exceed 1 metre in height.</p>
<p>It is one of the most beautiful underwater landscapes in the western Mediterranean, popular among both amateur divers and underwater photographers. The colonies are either male or female and all originate from the planula, a free-swimming or crawling larva type common among Cnidaria. Egg-shaped, the planula uses hairlike projections called cilia to propel itself through the water. It grows slowly (2 to 3 cm/year at most) and can live several decades.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/454778/original/file-20220328-19-2271qa.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454778/original/file-20220328-19-2271qa.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454778/original/file-20220328-19-2271qa.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454778/original/file-20220328-19-2271qa.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454778/original/file-20220328-19-2271qa.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454778/original/file-20220328-19-2271qa.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454778/original/file-20220328-19-2271qa.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The large purple gorgonian (<em>Paramuricea clavata</em>) is a typical species from the circalittoral rocky bottoms and coralligenous bottoms in the Mediterranean.</span>
<span class="attribution"><span class="source">Dorian Guillemain, CC BY-NC-ND</span></span>
</figcaption>
</figure>
<h2>“Animal forests” weakened by human activities…</h2>
<p>Purple gorgonian beds, like those of other gorgonians, are fragile and vulnerable to human activities in coastal areas. In the Mediterranean, these populations are also regularly affected by the impact of climate change.</p>
<p>Fishing nets and anchors can tear off the fragile colonies or cause injury (necrosis) to the living tissue covering their horny skeletons. Creatures that live on top of other organisms – known as epibion organisms – then proceed to colonise the beds’ exposed areas, threatening the colony’s survival.</p>
<p>Excessive input of sediment in marine environment – referred to as hypersedimentation and linked to coastal constructions and the changes of the courses of rivers – is also a threat to the populations of gorgonians.</p>
<p>Although they have been spared from warming Mediterranean waters, the <em>Paramuricea clavata</em> are locally impacted by fishing and above all by recreational fishing. The vast rock shelf colonised by these giant gorgonians is home to scores of sea breams in the autumn, which themselves are prized by amateur fishermen.</p>
<p>Up to 180 boats were counted on <a href="https://parcmarincotebleue.fr/">29 October 2016</a> during the sea bream reproduction period. Anchors and fishing lines uprooted many giant colonies. It therefore appears essential to control visitor numbers in this conservation area if we are to enable this unique natural heritage to coexist with human activity.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/454779/original/file-20220328-13-rkkxo8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454779/original/file-20220328-13-rkkxo8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454779/original/file-20220328-13-rkkxo8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454779/original/file-20220328-13-rkkxo8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454779/original/file-20220328-13-rkkxo8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454779/original/file-20220328-13-rkkxo8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454779/original/file-20220328-13-rkkxo8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A fishing net caught in a settlement of purple gorgonians. When the net is lifted, it will cause colonies to be torn off and the living tissue covering their corneal skeleton to die off.</span>
<span class="attribution"><span class="source">Benoist de Vogüé/CC BY-NC-ND</span></span>
</figcaption>
</figure>
<h2>… and by climate change</h2>
<p>Human activities in the coastal area are not the only danger faced by gorgonians. In recent decades, climate change has caused the strong wind on the Provencal coast known as the Mistral to weaken during increasingly long periods. This, in turn, has provoked thermal anomalies in the water column.</p>
<p>The result of this is the submergence of the surface warm water layers (temperature >22 °C) for stretches of several weeks. The latter can be fatal to the gorgonian populations, which are usually exposed to cooler temperatures (around 13 to 15 °C).</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/454780/original/file-20220328-19-uz09rx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/454780/original/file-20220328-19-uz09rx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=458&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454780/original/file-20220328-19-uz09rx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=458&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454780/original/file-20220328-19-uz09rx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=458&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454780/original/file-20220328-19-uz09rx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=576&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454780/original/file-20220328-19-uz09rx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=576&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454780/original/file-20220328-19-uz09rx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=576&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A living tissue slowly dies off, exposing the corneal skeleton of a gorgonian which was subsequently covered by epibiont organisms. This necrosis was caused by a thermal anomaly observed in 2014 at a depth of up to 30 metres.</span>
<span class="attribution"><span class="source">Benoist de Vogüé</span></span>
</figcaption>
</figure>
<p>In 1999, a <a href="https://www.academia.edu/10389935/Mortalit%C3%A9_massive_d_invert%C3%A9br%C3%A9s_marins_un_%C3%A9v%C3%A9nement_sans_pr%C3%A9c%C3%A9dent_en_M%C3%A9diterran%C3%A9e_nord_occidentale">vast thermal anomaly</a> affected gorgonian populations in the western Mediterranean stretching from Spain to Italy. Apart from gorgonians, about 20 other species (sponges, bivalve molluscs, bryozoans, ascidians) were also affected.
The anomaly was characterised by the presence of a column of warm water (23 to 24°C) at a depth ranging from 40 to 60 metres for a month. Other events of this type were then observed in 2003, 2006 and 2009, affecting the gorgonians to a greater or lesser extent.</p>
<p>Factors such as the gorgonians’ genetic makeup or microbiota will dictate how they fare in the face of heat stresses. In the coming decades, <a href="https://theconversation.com/suffering-in-the-heat-the-rise-in-marine-heatwaves-is-harming-ocean-species-112839">significant climatic changes</a> are expected to impact upon these species’ location and distribution. </p>
<h2>Discovering a unique deep-sea community</h2>
<p>Although gorgonian populations in the Mediterranean are well researched down to 50 metres, little is known about those farther below. A unique settlement was discovered a few decades ago off the <em>Côte bleue</em> (northern bay of Marseille) at a depth of 50 to 60 metres. This settlement occupies a vast rock shelf extending over nearly 2,500 hectares.</p>
<p>It is characterised by a high density of gorgonians, but above all by the presence of giant colonies. Hovering between 1.50 and 1.80 metres, these corals are probably around a century old.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/454781/original/file-20220328-23-1ps85am.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/454781/original/file-20220328-23-1ps85am.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/454781/original/file-20220328-23-1ps85am.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/454781/original/file-20220328-23-1ps85am.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/454781/original/file-20220328-23-1ps85am.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/454781/original/file-20220328-23-1ps85am.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/454781/original/file-20220328-23-1ps85am.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A diver inspects a human-sized purple gorgonian (<em>Paramuricea clavata</em>) in the 60-metre-deep, rocky bottom off the <em>Côte bleue</em>, north of Marseille.</span>
<span class="attribution"><span class="source">Romain Bricoult</span></span>
</figcaption>
</figure>
<p>Recent studies have sought to explain the reasons behind the species’ gigantism and tightly knit networks (REFUCLIM programme) and distribution (GIGOR programme). The results seem to show that, apart from their morphology, these gorgonians are genetically unique and clearly distinct from those found at shallower depths.</p>
<p>The environment surrounding them is unique. Not only are the gorgonians regularly subjected to strong inputs of organic matter linked to the proximity of the Rhône’s mouth, but the bottom currents are generally weak. The combination of these two parameters allows the gorgonians to reach exceptional sizes.</p>
<p>One of the issues at stake is that these deep settlements can constitute <a href="https://www.nature.com/articles/s41598-019-41929-0">refuge populations</a>, which are relatively spared from global warming, making them all the more important for the species’ survival.</p>
<p>The study of deep-sea gorgonian populations is a major area of research in the years to come, not only to initiate appropriate protection measures, but also to better understand their connections with the populations inhabiting the sea’s shallower depths.</p><img src="https://counter.theconversation.com/content/180194/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stéphane Sartoretto received funding from the EC2CO program (coordination: CNRS/INSU) et from AFB (French Agency for the Biodiversité). </span></em></p>Forming tightly woven populations, these bush-like corals offer a refuge to a myriad of marine species.Stéphane Sartoretto, Chercheur en écologie marine (écosystèmes benthiques méditerranéens de substrat dur), IfremerLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1664122021-08-20T22:24:52Z2021-08-20T22:24:52ZCoral, meet coral: how selective breeding may help the world’s reefs survive ocean heating<figure><img src="https://images.theconversation.com/files/417162/original/file-20210820-25-camnn7.jpg?ixlib=rb-1.1.0&rect=25%2C0%2C2892%2C1926&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Anna Scott</span>, <span class="license">Author provided</span></span></figcaption></figure><p>A single generation of selective breeding can make corals better able to withstand extreme temperatures, according to our new research. The discovery could offer a lifeline to reefs <a href="https://www.ipcc.ch/assessment-report/ar6/">threatened by the warming of the world’s oceans</a>.</p>
<p>Our research, <a href="https://advances.sciencemag.org/content/7/34/eabg6070">published in Science Advances</a>, shows corals from some of the world’s hottest seas can transfer beneficial genes associated with heat tolerance to their offspring, even when crossbred with corals that have never experienced such temperatures. </p>
<p>Across the world, corals vary widely, both in the temperatures they experience and their ability to withstand high temperatures without becoming stressed or dying. In the Persian Gulf, corals have <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.13250">genetically adapted</a> to extreme water temperatures, tolerating summer conditions above 34°C for weeks at a time, and withstanding daily averages up to 36°C. </p>
<p>These water temperatures are 2-4°C higher than any other region where corals grow, and are on a par with end-of-century projections for reefs outside the Persian Gulf.</p>
<p>This led us to ask whether beneficial gene variants could be transferred to coral populations that are naïve to these temperature extremes. To find out, we collected fragments of <em>Platygyra daedalea</em> corals from the Persian Gulf, and cross-bred them with corals of the same species from the Indian Ocean, where summer temperatures are much cooler. </p>
<figure class="align-center ">
<img alt="Platygyra coral colony" src="https://images.theconversation.com/files/417167/original/file-20210820-15-1qsm7dy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/417167/original/file-20210820-15-1qsm7dy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/417167/original/file-20210820-15-1qsm7dy.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/417167/original/file-20210820-15-1qsm7dy.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/417167/original/file-20210820-15-1qsm7dy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/417167/original/file-20210820-15-1qsm7dy.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/417167/original/file-20210820-15-1qsm7dy.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Platygyra, a brain-shaped coral found in many parts of the world.</span>
<span class="attribution"><span class="source">Emily Howells</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We then heat-stressed the resulting offspring (more than 12,000 individual coral larvae) to see whether they could withstand temperatures of 33°C and 36°C — the summer maximums of their parents’ respective locations. </p>
<h2>Immediate gains</h2>
<p>We found an immediate transfer of heat tolerance when Indian Ocean mothers were crossed with Persian Gulf fathers. These corals showed an 84% increase in survival at high temperatures relative to purebred Indian Ocean corals, making them similarly resilient to purebred Persian Gulf corals. </p>
<p>Genome sequencing confirmed that gains in heat tolerance were due to the inheritance of beneficial gene variants from the Persian Gulf corals. Most Persian Gulf fathers produced offspring that were better able to withstand heat stress, and these fathers and their offspring had crucial variants associated with better heat tolerance. </p>
<p>Conversely, most Indian Ocean fathers produced offspring that were less able to survive heat stress, and were less likely to have gene variants associated with heat tolerance.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/gene-editing-is-revealing-how-corals-respond-to-warming-waters-it-could-transform-how-we-manage-our-reefs-143444">Gene editing is revealing how corals respond to warming waters. It could transform how we manage our reefs</a>
</strong>
</em>
</p>
<hr>
<h2>Survival of the fittest</h2>
<p>Encouragingly, gene variants associated with heat tolerance were not exclusive to Persian Gulf corals. Two fathers from the Indian Ocean produced offspring with unexpectedly high survival under heat stress, and had some of the same tolerance-associated gene variants that are prevalent in Persian Gulf corals. </p>
<p>This suggests that some populations have genetic variation upon which natural selection can act as the world’s oceans grow hotter. Selective breeding might be able to accelerate this process.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/heat-tolerant-corals-can-create-nurseries-that-are-resistant-to-bleaching-116675">Heat-tolerant corals can create nurseries that are resistant to bleaching</a>
</strong>
</em>
</p>
<hr>
<p>We are now assessing the genetic basis for heat tolerance in the same species of coral on the Great Barrier Reef and in Western Australia. We want to find out what gene variants are associated with heat tolerance, how these variants are distributed within and among reefs, and whether they are the same as those that allow corals in the Persian Gulf to survive such extreme temperatures. </p>
<p>This knowledge will help us understand the potential for Australian corals to adapt to rapid warming. </p>
<p>Although our study shows selective breeding can significantly improve the resilience of corals to ocean warming, we don’t yet know whether there are any trade-offs between thermal tolerance and other important traits, and whether there are significant <a href="https://onlinelibrary.wiley.com/doi/10.1111/eva.13154">genetic risks</a> involved in such breeding. </p>
<figure class="align-center ">
<img alt="Platygyra larvae" src="https://images.theconversation.com/files/417168/original/file-20210820-13-bj4n3f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/417168/original/file-20210820-13-bj4n3f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=483&fit=crop&dpr=1 600w, https://images.theconversation.com/files/417168/original/file-20210820-13-bj4n3f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=483&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/417168/original/file-20210820-13-bj4n3f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=483&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/417168/original/file-20210820-13-bj4n3f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=606&fit=crop&dpr=1 754w, https://images.theconversation.com/files/417168/original/file-20210820-13-bj4n3f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=606&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/417168/original/file-20210820-13-bj4n3f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=606&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Platygyra larvae. It remains to be seen whether the genetic benefits of heat-tolerance genes persist throughout life.</span>
<span class="attribution"><span class="source">Emily Howells</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Our study was done on coral larvae without the algae that live in close harmony with corals after they settle on reefs. So it will also be important to examine whether the genetic improvements to heat tolerance continue into the corals’ later life stages, when they team up with these algae.</p>
<p>Of course, saving corals from the perils of ocean warming will require action on multiple fronts — there is no silver bullet. Selective breeding might provide some respite to particular coral populations, but it won’t be enough to protect entire ecosystems, and nor is it a substitute for the urgent reduction of greenhouse emissions needed to limit the oceans’ warming.</p><img src="https://counter.theconversation.com/content/166412/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Emily Howells receives funding from the Reef Restoration and Adaptation Program, the Hermon Slade Foundation, and National Geographic. </span></em></p><p class="fine-print"><em><span>David Abrego receives funding from the Reef Restoration and Adaptation Program. </span></em></p>Corals in the Persian Gulf are tough - they can withstand temperatures that would kill corals elsewhere. And there’s good news: it’s easy to cross-breed their heat-tolerance genes into other corals.Emily Howells, Senior Research Fellow in Marine Biology, Southern Cross UniversityDavid Abrego, Lecturer, National Marine Science Centre, Southern Cross UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1637142021-07-01T19:54:17Z2021-07-01T19:54:17ZAlmost 60 coral species around Lizard Island are ‘missing’ – and a Great Barrier Reef extinction crisis could be next<figure><img src="https://images.theconversation.com/files/409251/original/file-20210701-17-jh9yhh.JPG?ixlib=rb-1.1.0&rect=3%2C0%2C2580%2C1940&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Michael Emslie</span></span></figcaption></figure><p>The federal government has <a href="https://theconversation.com/is-australia-really-doing-enough-for-the-great-barrier-reef-why-criticisms-of-unescos-in-danger-recommendation-dont-stack-up-163641">opposed</a> a <a href="https://theconversation.com/australian-government-was-blindsided-by-un-recommendation-to-list-great-barrier-reef-as-in-danger-but-its-no-great-surprise-163159">recommendation</a> by a United Nations body that the Great Barrier Reef be listed as “in danger”. But there’s no doubt the natural wonder is in dire trouble. In <a href="https://doi.org/10.1007/s00338-021-02144-4">new research</a>, my colleagues and I provide fresh insight into the plight of many coral species.</p>
<p>Worsening climate change, and subsequent <a href="https://www.nature.com/articles/s41586-018-0383-9">marine heatwaves</a>, have led to mass coral deaths on tropical reefs. However, there are few estimates of how reduced overall coral cover is linked to declines in particular coral species. </p>
<p>Our research examined 44 years of coral distribution records around Lizard Island, at the northern end of the Great Barrier Reef. We found 16% of coral species have not been seen for many years and are at risk of either local extinction, or disappearing from parts of their local range.</p>
<p>This is alarming, because local extinctions often signal wider regional – and ultimately global – species extinction events. </p>
<figure class="align-center ">
<img alt="Healthy coral near Lizard Island in 2011, top, then six years later after two bleaching events, bottom." src="https://images.theconversation.com/files/409253/original/file-20210701-23-11ewxkb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/409253/original/file-20210701-23-11ewxkb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=711&fit=crop&dpr=1 600w, https://images.theconversation.com/files/409253/original/file-20210701-23-11ewxkb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=711&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/409253/original/file-20210701-23-11ewxkb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=711&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/409253/original/file-20210701-23-11ewxkb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=894&fit=crop&dpr=1 754w, https://images.theconversation.com/files/409253/original/file-20210701-23-11ewxkb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=894&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/409253/original/file-20210701-23-11ewxkb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=894&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Healthy coral near Lizard Island in 2011, top, then six years later after two bleaching events, bottom.</span>
<span class="attribution"><span class="source">Zoe Richards</span></span>
</figcaption>
</figure>
<h2>Sobering findings</h2>
<p>The Lizard Island reef system is 270 kilometres north of Cairns. It has suffered major disturbances over the past four decades: repeated outbreaks of crown-of-thorns seastars, category 4 cyclones in 2014 and 2015, and coral bleaching events in 2016, 2017 and 2020.</p>
<p>Our research focused on “hermatypic” corals around Lizard Island. These corals deposit calcium carbonate and form the hard framework of the reef. </p>
<p>We undertook hard coral biodiversity surveys four times between 2011 and 2020, across 14 sites. We combined the results with published and photographic species records from 1976 to 2020.</p>
<figure class="align-right ">
<img alt="red fleshy coral with blue spots" src="https://images.theconversation.com/files/409239/original/file-20210701-21296-1ge6zpm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/409239/original/file-20210701-21296-1ge6zpm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=797&fit=crop&dpr=1 600w, https://images.theconversation.com/files/409239/original/file-20210701-21296-1ge6zpm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=797&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/409239/original/file-20210701-21296-1ge6zpm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=797&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/409239/original/file-20210701-21296-1ge6zpm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1001&fit=crop&dpr=1 754w, https://images.theconversation.com/files/409239/original/file-20210701-21296-1ge6zpm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1001&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/409239/original/file-20210701-21296-1ge6zpm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1001&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Micromussa lordhowensis is popular in the aquarium trade.</span>
<span class="attribution"><span class="source">Zoe Richards</span></span>
</figcaption>
</figure>
<p>Of 368 hard coral species recorded around Lizard Island, 28 (7.6%) have not been reliably recorded since before 2011 and may be at risk of local extinction. A further 31 species (8.4%) have not been recorded since 2015 and may be at risk of range reduction (disappearance from parts of its local range).</p>
<p>The “missing” coral species include:</p>
<ul>
<li><p><em>Acropora abrotanoides</em>, a robust branching shallow water coral that lives on the reef crest and reef flat has not been since since 2009</p></li>
<li><p><em>Micromussa lordhowensis</em>, a low-growing coral with colourful fleshy polyps. Popular in the aquarium trade, it often grows on reef slopes but has not been seen since 2005</p></li>
<li><p><em>Acropora aspera</em>, a branching coral which prefers very shallow water and has been recorded just once, at a single site, since 2011. </p></li>
</ul>
<p>The finding that 59 coral species are at risk of local extinction or range reduction is significant. Local range reductions are often precursors to local species extinctions. And local species extinctions are often precursors to regional, and ultimately global, extinction events.</p>
<p>Each coral species on the reef has numerous vital functions. It might provide habitat or food to other reef species, or <a href="https://www.mdpi.com/1660-3397/17/8/468">biochemicals</a> which may benefit human health. One thing is clear: every coral species matters. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-outlook-for-coral-reefs-remains-grim-unless-we-cut-emissions-fast-new-research-160251">The outlook for coral reefs remains grim unless we cut emissions fast — new research</a>
</strong>
</em>
</p>
<hr>
<figure class="align-center ">
<img alt="reddish coral underwater" src="https://images.theconversation.com/files/409235/original/file-20210701-21-8gnrht.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/409235/original/file-20210701-21-8gnrht.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/409235/original/file-20210701-21-8gnrht.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/409235/original/file-20210701-21-8gnrht.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/409235/original/file-20210701-21-8gnrht.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/409235/original/file-20210701-21-8gnrht.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/409235/original/file-20210701-21-8gnrht.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Acropa abrotanoides, one of the corals ‘missing’ from around Lizard Island.</span>
<span class="attribution"><span class="source">Zoe Richards</span></span>
</figcaption>
</figure>
<h2>A broader extinction crisis?</h2>
<p>As human impacts and climate threats mount, there is growing concern about the resilience of coral biodiversity. Our research suggests such concerns are well-founded at Lizard Island.</p>
<p>Coral reef communities are dynamic, and so detecting species loss can be difficult. Our research found around Lizard Island, the diversity of coral species fluctuated over the past decade. Significant declines were recorded from 2011 to 2017, but diversity recovered somewhat in the three following years.</p>
<p>Local extinctions often happen incrementally and can therefore be “invisible”. To detect them, and to account for natural variability in coral communities, long-term biodiversity monitoring across multiple locations and time frames is needed.</p>
<figure class="align-center ">
<img alt="Green coral" src="https://images.theconversation.com/files/409248/original/file-20210701-27-1r08ziv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/409248/original/file-20210701-27-1r08ziv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/409248/original/file-20210701-27-1r08ziv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/409248/original/file-20210701-27-1r08ziv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/409248/original/file-20210701-27-1r08ziv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/409248/original/file-20210701-27-1r08ziv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/409248/original/file-20210701-27-1r08ziv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Acropora aspera has been recorded just once, at a single location, since 2011.</span>
<span class="attribution"><span class="source">Anne Hoggett</span></span>
</figcaption>
</figure>
<p>In most locations however, data on the distribution and abundance of all coral species in a community is lacking. This means it can be hard to assess changes, and to understand the damage that climate change and other human-caused stressors are having on each species.</p>
<p>Only with this extra information can scientists conclusively say if the level of local extinction risk at Lizard Island indicates a risk that coral species may become extinct elsewhere – across the Great Barrier Reef and beyond. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/is-australia-really-doing-enough-for-the-great-barrier-reef-why-criticisms-of-unescos-in-danger-recommendation-dont-stack-up-163641">Is Australia really doing enough for the Great Barrier Reef? Why criticisms of UNESCO’s 'in danger' recommendation don’t stack up</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/163714/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Zoe Richards receives funding from the Australian Research Council.
Zoe Richards is Marine Invertebrate Curator at the Western Australian Museum.</span></em></p>Researchers found 16% of coral species have not been seen for many years. This finding is alarming, because local extinctions suggest global extinctions may be looming.Zoe Richards, Senior Research Fellow, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1597922021-04-29T14:38:49Z2021-04-29T14:38:49ZWatching a coral reef die as climate change devastates one of the most pristine tropical island areas on Earth<figure><img src="https://images.theconversation.com/files/397728/original/file-20210429-13-1cf9nq9.jpg?ixlib=rb-1.1.0&rect=0%2C8%2C1917%2C1212&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Chagos Reef was vibrant before the heat wave.</span> <span class="attribution"><a class="source" href="https://www.livingoceansfoundation.org/publication/global-reef-expedition-chagos-archipelago-final-report/">Ken Marks/Khaled bin Sultan Living Oceans Foundation</a></span></figcaption></figure><p>The <a href="https://en.wikipedia.org/wiki/Chagos_Archipelago#/media/File:Chagos_map.PNG">Chagos Archipelago</a> is one of the most remote, seemingly idyllic places on Earth. Coconut-covered sandy beaches with incredible bird life rim tropical islands in the Indian Ocean, hundreds of miles from any continent. Just below the waves, coral reefs stretch for miles along an <a href="https://www.researchgate.net/figure/Satellite-bathymetry-map-of-the-western-Indian-Ocean-basin-Approximate-aerial-extent-of_fig1_320835153">underwater mountain chain</a>.</p>
<p>It’s a paradise. At least it was before the heat wave.</p>
<p>When I first explored the Chagos Archipelago 15 years ago, the underwater view was incredible. Schools of brilliantly colored fish in blues, yellows and oranges darted among the corals of a vast, healthy reef system. Sharks and other large predators swam overhead. Because the archipelago is so remote and sits in one of the largest <a href="https://chagos-trust.org/chagos/overview">marine protected areas</a> on the planet, it has been sheltered from industrial fishing fleets and other activities that can harm the coastal environment.</p>
<p>But it can’t be protected from climate change.</p>
<figure class="align-center ">
<img alt="A diver carries a plastic pipe for measuring while swimming over a variety of corals" src="https://images.theconversation.com/files/397204/original/file-20210426-15-ng6gsy.jpg?ixlib=rb-1.1.0&rect=480%2C586%2C1097%2C689&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/397204/original/file-20210426-15-ng6gsy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/397204/original/file-20210426-15-ng6gsy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/397204/original/file-20210426-15-ng6gsy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/397204/original/file-20210426-15-ng6gsy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/397204/original/file-20210426-15-ng6gsy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/397204/original/file-20210426-15-ng6gsy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A diver documents the coral reefs in the Chagos Archipelago.</span>
<span class="attribution"><a class="source" href="https://www.livingoceansfoundation.org/publication/global-reef-expedition-chagos-archipelago-final-report/">Khaled bin Sultan Living Oceans Foundation</a></span>
</figcaption>
</figure>
<p>In 2015, a marine heat wave struck, harming coral reefs worldwide. <a href="https://people.miami.edu/profile/spurkis@rsmas.miami.edu">I’m a marine biologist</a> at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, and I was with a team of researchers on a <a href="https://www.livingoceansfoundation.org/global-reef-expedition/global-reef-expedition-final-reports/">10-year global expedition to map the world’s reefs</a>, led by the <a href="https://www.livingoceansfoundation.org/">Khaled bin Sultan Living Oceans Foundation</a>, wrapping up our work in the Chagos Archipelago at the time. Our report on the state of the reefs there <a href="https://www.livingoceansfoundation.org/publication/global-reef-expedition-chagos-archipelago-final-report/">was just published</a> in spring 2021.</p>
<p>As the water temperature rose, the corals began to bleach. To the untrained eye, the scene would have looked fantastic. When the water heats up, corals become stressed and they expel the tiny algae called dinoflagellates that live in their tissue. Bleaching isn’t as simple as going from a living coral to a bleached white one, though. After they expel the algae, the corals turn fluorescent pinks and blues and yellows as they produce chemicals to <a href="https://doi.org/10.1016/j.cub.2020.04.055">protect themselves from the Sun’s harmful rays</a>. The entire reef was turning psychedelic colors.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/397178/original/file-20210426-13-v15dqm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two bright pink coral mounds" src="https://images.theconversation.com/files/397178/original/file-20210426-13-v15dqm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/397178/original/file-20210426-13-v15dqm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/397178/original/file-20210426-13-v15dqm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/397178/original/file-20210426-13-v15dqm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/397178/original/file-20210426-13-v15dqm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/397178/original/file-20210426-13-v15dqm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/397178/original/file-20210426-13-v15dqm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Just before they turned white, the corals turned abnormally bright shades.</span>
<span class="attribution"><a class="source" href="https://www.livingoceansfoundation.org/publication/global-reef-expedition-chagos-archipelago-final-report/">Phil Renaud/Khaled bin Sultan Living Oceans Foundation</a></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Large fish and schools of fish swimming above the reef" src="https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Chagos archipelago is home to some 800 species of fish, including rays, skates and dozens of varieties of shark.</span>
<span class="attribution"><a class="source" href="https://www.livingoceansfoundation.org/publication/global-reef-expedition-chagos-archipelago-final-report/">Phil Renaud/Khaled bin Sultan Living Oceans Foundation</a></span>
</figcaption>
</figure>
<p>That explosion of color is rare, and it doesn’t last long. Over the following week, we watched the corals turn white and start to die. It wasn’t just small pieces of the reef that were bleaching – it was happening across hundreds of square miles.</p>
<p>What most people think of as a coral is actually many tiny colonial polyps that build calcium carbonate skeletons. With their algae gone, the coral polyps could still feed by plucking morsels out of the water, but their metabolism slows without the algae, which provide more nutrients <a href="https://oceanservice.noaa.gov/education/tutorial_corals/coral02_zooxanthellae.html">through photosynthesis</a>. They were left desperately weakened and more vulnerable to diseases. We could see diseases taking hold, and that’s what finished them off.</p>
<p>We were witnessing the death of a reef.</p>
<figure class="align-center ">
<img alt="A large mushroom-shaped coral structure, half of it turned white from bleaching" src="https://images.theconversation.com/files/397197/original/file-20210426-19-2eyjzx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/397197/original/file-20210426-19-2eyjzx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/397197/original/file-20210426-19-2eyjzx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/397197/original/file-20210426-19-2eyjzx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/397197/original/file-20210426-19-2eyjzx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/397197/original/file-20210426-19-2eyjzx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/397197/original/file-20210426-19-2eyjzx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Corals beginning to bleach in the Chagos archipelago.</span>
<span class="attribution"><a class="source" href="https://www.livingoceansfoundation.org/publication/global-reef-expedition-chagos-archipelago-final-report/">Phil Renaud/Khaled bin Sultan Living Oceans Foundation</a></span>
</figcaption>
</figure>
<h2>Rising temperatures increase the heat wave risk</h2>
<p>The devastation of the Chagos Reef wasn’t happening in isolation.</p>
<p>Over the past century, <a href="https://www.ncdc.noaa.gov/cag/global/time-series/globe/ocean/ytd/12/1880-2017">sea surface temperatures</a> have risen by an average of <a href="https://www.epa.gov/climate-indicators/climate-change-indicators-sea-surface-temperature">about 0.13 degrees Celsius</a> (0.23 F) per decade as the oceans absorb the vast majority of greenhouse gas emissions from human activities, largely from the burning of fossil fuels. The temperature increase and changing ocean chemistry affects sea life of all kinds, from <a href="https://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F">deteriorating the shells of oysters and tiny pteropods</a>, an essential part of the food chain, to causing fish populations to migrate to cooler water. </p>
<p>Corals can become stressed when temperatures around them <a href="https://coralreefwatch.noaa.gov/satellite/methodology/methodology.php">rise just 1 C</a> (1.8 F) above their tolerance level. With water temperature elevated from global warming, even a minor heat wave can become devastating.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/IEWJAEkGeNk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>In 2015, the ocean heat from a strong <a href="https://oceanservice.noaa.gov/facts/ninonina.html">El Niño</a> event triggered the mass bleaching in the Chagos reefs and <a href="https://www.climate.gov/news-features/event-tracker/survey-photos-reveal-damage-year%E2%80%99s-global-coral-bleaching-event">around the world</a>. It was the third global bleaching on record, following events in <a href="http://www.reefcheck.org/wp-content/uploads/2020/07/Ambio1999.pdf">1998</a> and <a href="https://www.climate.gov/news-features/videos/coral-bleaching-alarm-2010">2010</a>.</p>
<p>Bleaching doesn’t just affect the corals – entire reef systems and the fish that feed, spawn and live among the coral branches suffer. One <a href="https://doi.org/10.1073/pnas.0401277101">study of reefs</a> around Papua New Guinea in the southwest Pacific found that about 75% of the reef fish species declined after the 1998 bleaching, and many of those species declined by more than half.</p>
<figure class="align-center ">
<img alt="Two bright orange fish with white bands swim past an anemone" src="https://images.theconversation.com/files/397200/original/file-20210426-21-24e0zc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/397200/original/file-20210426-21-24e0zc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/397200/original/file-20210426-21-24e0zc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/397200/original/file-20210426-21-24e0zc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/397200/original/file-20210426-21-24e0zc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/397200/original/file-20210426-21-24e0zc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/397200/original/file-20210426-21-24e0zc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Most corals are brown or green. Fish and anemones bring color to the reefs.</span>
<span class="attribution"><a class="source" href="https://www.livingoceansfoundation.org/publication/global-reef-expedition-chagos-archipelago-final-report/">Ken Marks/Khaled bin Sultan Living Oceans Foundation</a></span>
</figcaption>
</figure>
<figure class="align-center ">
<img alt="Starfish on a coral" src="https://images.theconversation.com/files/397603/original/file-20210428-19-1j2eryy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/397603/original/file-20210428-19-1j2eryy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/397603/original/file-20210428-19-1j2eryy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/397603/original/file-20210428-19-1j2eryy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/397603/original/file-20210428-19-1j2eryy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/397603/original/file-20210428-19-1j2eryy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/397603/original/file-20210428-19-1j2eryy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Noduled sea stars are among the reef’s diverse species.</span>
<span class="attribution"><a class="source" href="https://www.livingoceansfoundation.org/global-reef-expedition/">Ken Marks/Khaled bin Sultan Living Oceans Foundation</a></span>
</figcaption>
</figure>
<p>Research shows marine heat waves are now about <a href="http://doi.org/10.1126/science.aba0690">20 times more likely</a> than they were just four decades ago, and they tend to be hotter and last longer. We’re at the point now that some places in the world are anticipating coral bleaching every couple of years.</p>
<p>That increasing frequency of heat waves is a death knell for reefs. They don’t have time to recover before they get hit again.</p>
<p><iframe id="IS1fT" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/IS1fT/4/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<h2>Where we saw signs of hope</h2>
<p>During the <a href="https://www.livingoceansfoundation.org/global-reef-expedition/global-reef-expedition-final-reports/">Global Reef Expedition</a>, we visited over 1,000 reefs around the world. Our mission was to conduct standardized surveys to assess the state of the reefs and map the reefs in detail so scientists could document and hopefully respond to changes in the future. With that knowledge, countries can plan more effectively to protect the reefs, important national resources, providing <a href="https://reefresilience.org/value-of-reefs/">hundreds of billions of dollars a year</a> in economic value while also <a href="https://oceanservice.noaa.gov/facts/coral_protect.html">protecting coastlines</a> from waves and storms.</p>
<p>We saw damage almost everywhere, from the <a href="https://www.livingoceansfoundation.org/global-reef-expedition/atlantic-ocean/inaguas-bahamas/">Bahamas</a> to the <a href="https://www.youtube.com/watch?v=7yisyMO-Xi0">Great Barrier Reef</a>.</p>
<p>Some reefs are able to survive heat waves better than others. Cooler, stronger currents, and even storms and cloudier areas can help prevent heat building up. But the global trend is not promising. The world has already <a href="https://www.nationalacademies.org/news/2019/06/protecting-coral-reefs-in-a-deteriorating-environment">lost 30% to 50% of its reefs</a> in the last 40 years, and scientists have warned that most of the remaining reefs <a href="https://www.ipcc.ch/2018/10/08/summary-for-policymakers-of-ipcc-special-report-on-global-warming-of-1-5c-approved-by-governments/">could be gone within decades</a>.</p>
<figure class="align-center ">
<img alt="Flat corals turning white as they bleach" src="https://images.theconversation.com/files/397202/original/file-20210426-21-nq77pb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/397202/original/file-20210426-21-nq77pb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/397202/original/file-20210426-21-nq77pb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/397202/original/file-20210426-21-nq77pb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/397202/original/file-20210426-21-nq77pb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/397202/original/file-20210426-21-nq77pb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/397202/original/file-20210426-21-nq77pb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Table corals bleaching in the Chagos Reef.</span>
<span class="attribution"><a class="source" href="https://www.livingoceansfoundation.org/publication/global-reef-expedition-chagos-archipelago-final-report/">Derek Manzello/Khaled bin Sultan Living Oceans Foundation</a></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/397179/original/file-20210426-21-1l2ahj7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diver with large sea turtle swimming over corals." src="https://images.theconversation.com/files/397179/original/file-20210426-21-1l2ahj7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/397179/original/file-20210426-21-1l2ahj7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/397179/original/file-20210426-21-1l2ahj7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/397179/original/file-20210426-21-1l2ahj7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/397179/original/file-20210426-21-1l2ahj7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/397179/original/file-20210426-21-1l2ahj7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/397179/original/file-20210426-21-1l2ahj7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The author, Sam Purkis, dives near a hawksbill turtle in the Chagos Archipelago.</span>
<span class="attribution"><a class="source" href="https://www.livingoceansfoundation.org/publication/global-reef-expedition-chagos-archipelago-final-report/">Derek Manzello/Khaled bin Sultan Living Oceans Foundation</a></span>
</figcaption>
</figure>
<p>While we see some evidence that certain marine species are <a href="https://phys.org/news/2021-04-climate-marine-species-poleward.html">moving to cooler waters</a> as the planet warms, a reef takes thousands of years to establish and grow, and it is limited by geography.</p>
<p>In the areas where we saw glimmers of hope, it was mostly due to good management. When a region can control other harmful human factors – such as overfishing, extensive coastal development, pollution and runoff – the <a href="https://blogs.scientificamerican.com/observations/a-bulwark-against-reef-destruction-in-a-warming-world/">reefs are healthier</a> and better able to handle the global pressures from climate change.</p>
<p>Establishing large marine protected areas is one of the most effective ways I’ve seen to <a href="http://doi.org/10.1098/rstb.2015.0210">protect coral reefs</a> because it limits those other harms.</p>
<figure class="align-center ">
<img alt="Pointed-nose fish among coral branches" src="https://images.theconversation.com/files/397195/original/file-20210426-19-7dtogm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/397195/original/file-20210426-19-7dtogm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/397195/original/file-20210426-19-7dtogm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/397195/original/file-20210426-19-7dtogm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/397195/original/file-20210426-19-7dtogm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/397195/original/file-20210426-19-7dtogm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/397195/original/file-20210426-19-7dtogm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Coral reefs are fish nurseries and feeding grounds. They also protect coast lines from storms and waves.</span>
<span class="attribution"><a class="source" href="https://www.livingoceansfoundation.org/publication/global-reef-expedition-chagos-archipelago-final-report/">Stephan Andrews/Khaled bin Sultan Living Oceans Foundation</a></span>
</figcaption>
</figure>
<figure class="align-center ">
<img alt="Brilliant blue fish swim in a coral reef" src="https://images.theconversation.com/files/397205/original/file-20210426-15-15m16st.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/397205/original/file-20210426-15-15m16st.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/397205/original/file-20210426-15-15m16st.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/397205/original/file-20210426-15-15m16st.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/397205/original/file-20210426-15-15m16st.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/397205/original/file-20210426-15-15m16st.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/397205/original/file-20210426-15-15m16st.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Some of the diversity of the Chagos Reef.</span>
<span class="attribution"><a class="source" href="https://www.livingoceansfoundation.org/publication/global-reef-expedition-chagos-archipelago-final-report/">Derek Manzello/Khaled bin Sultan Living Oceans Foundation</a></span>
</figcaption>
</figure>
<p>The Chagos marine protected area covers 640,000 square kilometers (250,000 square miles) with only one island currently inhabited – Diego Garcia, which houses a U.S. military base. The British government, which created the marine protected area in 2010, has been <a href="https://www.lawfareblog.com/chagos-archipelago-dispute-law-diplomacy-and-military-basing">under pressure to turn over control of the region</a> to the country of Mauritius, where former Chagos residents now live and which won a challenge over it in the International Court of Justice in 2020. Whatever happens with jurisdiction, the region would benefit from maintaining a high level of marine protection.</p>
<h2>A warning for other ecosystems</h2>
<p>The Chagos reefs could potentially recover – if they are spared from more heat waves. Even a 10% recovery would make the reefs stronger for when the next bleaching occurs. But recovery of a reef is measured in decades, not years.</p>
<p>So far, research missions that have returned to the Chagos reefs have found only meager recovery, if any at all.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Large fish and schools of fish swimming above the reef" src="https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/397198/original/file-20210426-21-txmdaj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Chagos Archipelago is home to some 800 species of fish, including rays, skates and dozens of varieties of shark.</span>
<span class="attribution"><a class="source" href="https://www.livingoceansfoundation.org/publication/global-reef-expedition-chagos-archipelago-final-report/">Phil Renaud/Khaled bin Sultan Living Oceans Foundation</a></span>
</figcaption>
</figure>
<p>We knew the reefs weren’t doing well under the insidious march of climate change in 2011, when the global reef expedition started. But it’s nothing like the intensity of worry we have now in 2021.</p>
<p>Coral reefs are the canary in the coal mine. Humans have collapsed other ecosystems before through overfishing, overhunting and development, but this is the first unequivocally tied to climate change. It’s a harbinger of what can happen to other ecosystems as they reach their survival thresholds.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/369797/original/file-20201117-13-180ibt9.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
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<p><strong><em>This story is part of <a href="https://theconversation.com/uk/topics/oceans-21-96784">Oceans 21</a></em></strong>
<br><em>Our series on the global ocean opened with <a href="https://oceans21.netlify.app/">five in-depth profiles</a>. Look for new articles on the state of our oceans in the lead-up to the U.N.’s next climate conference, COP26. The series is brought to you by The Conversation’s international network.</em></p><img src="https://counter.theconversation.com/content/159792/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sam Purkis does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Scientists watched in real time as rising ocean heat transformed the sprawling reef. It was a harbinger for ecosystems everywhere as the planet warms.Sam Purkis, Professor and Chair of the Department of Marine Sciences, University of MiamiLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1437762020-08-18T14:39:06Z2020-08-18T14:39:06ZCoral sex: how reproducing species in the lab could be key to restoring reefs in the wild<figure><img src="https://images.theconversation.com/files/353421/original/file-20200818-14-z0jebp.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3539%2C2654&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/acropora-coral-spawning-on-magnetic-island-1556924156">Coral Brunner/Shutterstock</a></span></figcaption></figure><p>Coral reefs host <a href="https://www.frontiersin.org/articles/10.3389/fmars.2017.00158/full">a quarter of all sea species</a>, but climate change, overfishing, and pollution could drive these ecosystems to extinction within a matter of decades. </p>
<p>Marine biologists have been racing to restore degraded reefs by collecting corals from the wild and breaking them into fragments. This encourages them to grow fast and quickly produces hundreds of smaller corals which can be raised in nurseries and eventually transplanted back onto the reef. </p>
<p>But if each fragment is an identical copy with one common parent, any resulting colony is likely to be genetically identical to the rest of the population. This matters – having a diverse range of genetically conferred traits can help insure reefs against disease and a rapidly changing environment.</p>
<p>So what if scientists could use sexual reproduction in coral restoration projects? In the wild, the stony coral species that compose the bulk of the world’s tropical reefs cast their sperm and eggs into the water column to reproduce. Corals often synchronise these mass spawning events with full moons, when tides are exceptionally high. This ensures powerful water currents disperse the eggs far and wide, so that they’re fertilised by sperm of distant colonies.</p>
<figure class="align-center ">
<img alt="A light shines on a tropical coral at night, illuminating sperm and egg cells in the water." src="https://images.theconversation.com/files/351952/original/file-20200810-18-6h7axy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/351952/original/file-20200810-18-6h7axy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/351952/original/file-20200810-18-6h7axy.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/351952/original/file-20200810-18-6h7axy.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/351952/original/file-20200810-18-6h7axy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/351952/original/file-20200810-18-6h7axy.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/351952/original/file-20200810-18-6h7axy.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Corals often broadcast their sperm and eggs during the full moon.</span>
<span class="attribution"><span class="source">Jenny Mallon</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Sexually produced offspring have a unique combination of genes from distinct parents, and this helps keep coral populations genetically diverse. Reefs restored with corals created by sexual reproduction are likely to be more resilient, though managing this process hasn’t been easy for scientists to do. But by working on one project in Mexico, I saw what is possible, and learned how to do it myself.</p>
<h2>Coral sex in the lab</h2>
<p>Coral reefs are so enormous they’re visible from space. But watching them spawn is surprisingly tricky. They only do it on a handful of nights each year and the exact date and time is determined by environmental factors that scientists are still working to fully understand. </p>
<p>Climate change is causing reefs with known spawning patterns to shift their timing too, <a href="https://science.sciencemag.org/content/365/6457/987.full%5D">making these events less frequent and predictable</a>. This makes it difficult for different colonies to synchronise spawning, reducing their chances of successful fertilisation in the wild. </p>
<p>The CORALIUM Laboratory of the National Autonomous University of Mexico is part of a <a href="https://www.secore.org">Caribbean-wide network</a> of dedicated coral spawning experts. Scientists here collect coral sperm and eggs from multiple Caribbean reefs in order to fertilise them in the lab. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/z9h-xyLlpro?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Javier Iturrieta, Akumal Dive Center & Thomas Vogt.</span></figcaption>
</figure>
<p>The team wait for the full moon to signal when corals are likely to spawn. Coral sperm and eggs are collected with floating nets and plastic containers, and divers take extreme care to avoid damaging the reef. The millions of sperm and eggs collected are rushed back to the lab where they’re cleaned and monitored all night as they undergo assisted fertilisation to begin life as free swimming larvae. These larvae are very sensitive to water quality, temperature and pathogens, so they need constant care. </p>
<p>Eventually, the larvae settle on hard surfaces where they change into polyps – the initial building blocks of a coral colony. In the ocean, these surfaces are often dead coral skeletons. In the lab, they are <a href="http://www.secore.org/site/our-work/detail/engineering-restoration.60.html">seeding units</a> – 3-D shapes designed by scientists at the conservation organisation <a href="http://www.secore.org/site/home.html">SECORE</a> to resemble coral rubble that can float on ocean currents before resting on reefs.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/352314/original/file-20200811-14-mntl05.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A selection of pieces of artificial coral rubble." src="https://images.theconversation.com/files/352314/original/file-20200811-14-mntl05.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/352314/original/file-20200811-14-mntl05.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/352314/original/file-20200811-14-mntl05.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/352314/original/file-20200811-14-mntl05.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/352314/original/file-20200811-14-mntl05.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/352314/original/file-20200811-14-mntl05.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/352314/original/file-20200811-14-mntl05.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Seeding units are designed to be carried naturally on currents and to right themselves on reefs.</span>
<span class="attribution"><span class="source">SECORE International/Amanda Baye</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Each juvenile produced this way carries a unique mix of genes which they will pass on to a new generation of corals. The resulting population has a stronger gene pool that can help it withstand new diseases and other threats. This long-term strategy also ensures sexual reproduction can continue on restored reefs, which would not be possible for a population composed of identical clones. </p>
<h2>Restoring Caribbean reefs</h2>
<p>The Caribbean may have lost as much as <a href="https://science.sciencemag.org/content/301/5635/958">80% of its coral cover since the mid-1970s</a>. The colonies that remain are now relatively isolated, reducing the chances of them being able to crossbreed. But in the controlled conditions of the lab, fertilisation rates of over 80% are common and larval survival is high. That means thousands of juvenile corals are reared until they’re ready for the reef after just a few weeks of incubation.</p>
<p>But with late night dives by experts, specialised materials for collecting spawn and a lab where fertilisation is carefully controlled, this work is often too expensive for smaller restoration projects. So scientists here have developed low-cost methods for lab spawning and are training teams from across the Caribbean to do it.</p>
<p>I took their course in 2016, and one year later, found myself setting up a new spawning site in Akumal, one hour south of the CORALIUM lab near Cancun. Coral spawning had never been observed here, but I trained volunteers from a local dive centre on how to spot the signs. On our fifth consecutive night dive, we saw the synchronised spawning of multiple colonies of Elkorn corals.</p>
<p>We set up a hotel room as a temporary lab with sterilised plastic larvae tanks and filtered seawater and produced thousands of coral babies for restoration sites. In 2018, we built a beachside coral spawning laboratory on a shoestring budget. Positioned under a tree, the breeze block structure has mosquito netting walls that allow the cool sea breeze to keep the tanks at a constant 28-29°C.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/352366/original/file-20200811-17-14brkl2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A laboratory interior with water-filled crates and a microscope." src="https://images.theconversation.com/files/352366/original/file-20200811-17-14brkl2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/352366/original/file-20200811-17-14brkl2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/352366/original/file-20200811-17-14brkl2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/352366/original/file-20200811-17-14brkl2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/352366/original/file-20200811-17-14brkl2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/352366/original/file-20200811-17-14brkl2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/352366/original/file-20200811-17-14brkl2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Larval rearing bins and a microscope are set up and ready for coral spawning.</span>
<span class="attribution"><span class="source">Jenny Mallon</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The lab was just about up and running in time for that year’s lunar eclipse. We hadn’t anticipated a mass spawn of so many colonies, so the lab inauguration was a chaos of colour coded collection cups from different sites and parent colonies.</p>
<p>Running a coral spawning site has been the most rewarding experience of my career so far. It is everything that research should be: cutting edge, dynamic and challenging. It’s what I signed up for when I became a marine scientist.</p><img src="https://counter.theconversation.com/content/143776/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jenny Mallon receives funding from the Coral Conservation Society. The work described here was completed in partnership with CORALIUM, SECORE International, Ridge to Reefs, Hotel Akumal Caribe and the Akumal Dive Center.</span></em></p>Sexual reproduction helps keep coral colonies diverse and resilient. Now, scientists are doing it in a lab to restock flagging reefs.Jennifer Mallon, PhD Candidate in Coral Reef Biogeochemistry, University of GlasgowLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1230452019-09-06T13:43:02Z2019-09-06T13:43:02ZCoral reefs: breakdown in iconic spawning puts species at risk of extinction – new research<figure><img src="https://images.theconversation.com/files/291254/original/file-20190906-175710-10b209h.jpg?ixlib=rb-1.1.0&rect=0%2C15%2C5184%2C3430&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Corals release millions of sperm and eggs in synchrony to reproduce.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/coral-spawning-underwater-165426125?src=-1-2">Rich Carey/Shutterstock</a></span></figcaption></figure><p>It’s rather tricky to reproduce if you’re stuck to the floor – unless you’re a coral. Their <a href="https://theconversation.com/explainer-mass-coral-spawning-a-wonder-of-the-natural-world-87253">spectacular spawning events</a> are a beautiful sight to behold. Once a year, they spill billions of sperm and eggs into the sea, peppering the deep blue with a palette of vivid reds, yellows, oranges, and whites.</p>
<p>But according to <a href="https://science.sciencemag.org/cgi/doi/10.1126/science.aax0110">new research</a>, some corals are no longer reproducing with the same clockwork timing, adding yet another survival threat to the long list already befalling reefs.</p>
<p>Corals are unlike any other animal on the planet. Thousands of polyps, each resembling an upside down jellyfish, live with each other in beds of limestone attached to the seabed. As they grow, they create the unified limestone skeleton we see as coral from the outside. Many of these coral colonies together create a complex three-dimensional reef structure that in turn <a href="https://coral.org/coral-reefs-101/coral-reef-ecology/coral-reef-biodiversity/">creates a home</a> for thousands of other plants and animals.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/291265/original/file-20190906-175682-dm4bkj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/291265/original/file-20190906-175682-dm4bkj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=903&fit=crop&dpr=1 600w, https://images.theconversation.com/files/291265/original/file-20190906-175682-dm4bkj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=903&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/291265/original/file-20190906-175682-dm4bkj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=903&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/291265/original/file-20190906-175682-dm4bkj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1135&fit=crop&dpr=1 754w, https://images.theconversation.com/files/291265/original/file-20190906-175682-dm4bkj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1135&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/291265/original/file-20190906-175682-dm4bkj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1135&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Corals release so many sperm and eggs that the slicks can often be seen from the air.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Freza_coral_5.jpg">LBM1948/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>To get around their firm attachment to the seabed, most coral species reproduce by the mass release of sperm and eggs directly into the water at the same time. This annual mass spawning is one of nature’s most iconic events – rising underwater snowstorms so thick that they create brightly coloured slicks on the sea surface, visible from high above.</p>
<p>Astonishingly, corals synchronise their reproduction despite not having a brain, nor any direct way of communicating between colonies. Sperm and eggs can only survive in the water for a few hours, so in the vast ocean space this synchrony is essential for a good chance of fertilisation.</p>
<p>Until recently, little more than this was known about the intricacies of coral reproduction. But in the context of rapid coral decline, researchers have started applying genetic and reproductive research techniques to understand how environmental conditions are impacting coral fertilisation.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-mass-coral-spawning-a-wonder-of-the-natural-world-87253">Explainer: mass coral spawning, a wonder of the natural world</a>
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</em>
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<p>The <a href="https://science.sciencemag.org/cgi/doi/10.1126/science.aax0110">new research</a> monitored mass spawnings on corals reefs in the northern Red Sea. The researchers compared spawning timings of five coral species between 2015 and 2018 to results from <a href="https://science.sciencemag.org/content/228/4705/1333">two other studies</a> conducted on the <a href="https://link.springer.com/article/10.1007/s002270050433">same species</a> in the 1980s. In the species <em>Acropora eurystoma</em>, they also measured various reproductive traits, such as the number of sperm and eggs within a colony, the number of colonies reproducing in a given area and the size of coral colonies in the area – an index of their age.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/zuHzNRynSLc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
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<p>In the 1980s, all the coral species monitored had one or two well-defined periods of spawning, where eggs and sperm were released within a few days of each other. But by the 2010s, some species released them over as many as a couple of months. With a lower concentration of eggs and sperm in the water at any one time, fertilisation becomes much rarer.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/291262/original/file-20190906-175673-tmy4nx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/291262/original/file-20190906-175673-tmy4nx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=199&fit=crop&dpr=1 600w, https://images.theconversation.com/files/291262/original/file-20190906-175673-tmy4nx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=199&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/291262/original/file-20190906-175673-tmy4nx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=199&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/291262/original/file-20190906-175673-tmy4nx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=250&fit=crop&dpr=1 754w, https://images.theconversation.com/files/291262/original/file-20190906-175673-tmy4nx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=250&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/291262/original/file-20190906-175673-tmy4nx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=250&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Left: Acropora eurystoma in ‘setting’ mode 30 minutes prior to spawning, in which egg-sperm bundles are already visible at the mouth opening of each polyp. Right: the colony spawning in synchrony.</span>
<span class="attribution"><a class="source" href="https://www.eurekalert.org/multimedia/pub/210319.php?from=440054">Tel Aviv University</a></span>
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</figure>
<p>Although visually the coral reefs appeared in overall good health, the researchers found that the corals that weren’t spawning at the same time had no baby corals. This means that affected species can appear to be abundant, but in reality be nearing extinction through reproductive failure.</p>
<h2>Threat and opportunity</h2>
<p>This is the first study to compare current spawning behaviour with historical data, providing evidence of increased desynchrony over time. Of course, there are many, many more coral species than the five measured in the current study, so we must be cautious of drawing general conclusions at this stage. However, evidence (without historical data for comparison) suggests that the <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0030486">same may be happening</a> in <a href="http://zoolstud.sinica.edu.tw/Journals/57/57-46.pdf">other parts of the world</a> too.</p>
<p>Unfortunately, it’s not yet known exactly what is causing the apparent decline in spawning synchrony, making it difficult to put forward a solution to the problem. Increases in <a href="https://elifesciences.org/articles/09991">light pollution from coastal development</a> and <a href="https://www.int-res.com/articles/meps2004/269/m269p121.pdf">hormone pollution from contraceptive pills</a> have recently been shown to disrupt the natural triggers for coral spawning. The same is true of <a href="https://royalsocietypublishing.org/doi/full/10.1098/rspb.2016.0011">water temperature</a>, which has increased by 1.2°C at the test site since the 1980s. However, further research is needed to establish whether these factors are causing corals to reproduce out of sync with each other.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/PR4bpVKVeQ4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
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<p>While these new advances in the understanding of coral reproductive biology are worrying, they also present opportunities. If we can identify why some corals are reproducing well and others not, we may be able to innovate <a href="https://theconversation.com/why-theres-still-hope-for-our-endangered-coral-reefs-104503">new conservation methods</a> that protect corals before they show signs of dying off. Using <a href="https://www.pnas.org/content/112/8/2307">selective breeding techniques</a>, for example, we may be able to imbue corals with greater resilience to the factors causing spawning desynchrony.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/heat-tolerant-corals-can-create-nurseries-that-are-resistant-to-bleaching-116675">Heat-tolerant corals can create nurseries that are resistant to bleaching</a>
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<p>In the meantime though, all we can do to keep the glimmer of hope alive for reefs is redouble international efforts to tackle climate breakdown, and manage coastal areas responsibly. Without such intervention, these ecosystems rich in economic, ecological and cultural value will soon succumb to the <a href="http://www.gbrmpa.gov.au/our-work/outlook-report-2019">multiple threats</a> it faces.</p><img src="https://counter.theconversation.com/content/123045/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Heidi Burdett receives funding from the Natural Environment Research Council (UK) and the Leverhulme Trust.</span></em></p>The largest reproductive event on the planet is under threat.Heidi Burdett, Research Fellow, Lyell Centre for Earth and Marine Science and Technology, Heriot-Watt UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1206712019-07-25T20:02:24Z2019-07-25T20:02:24ZExtreme weather caused by climate change has damaged 45% of Australia’s coastal habitat<figure><img src="https://images.theconversation.com/files/285435/original/file-20190724-110187-13zyuat.JPG?ixlib=rb-1.1.0&rect=0%2C287%2C2592%2C1652&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Bleached staghorn coral on the Great Barrier Reef. Many species are dependent on corals for food and shelter.</span> <span class="attribution"><span class="source">Damian Thomson</span>, <span class="license">Author provided</span></span></figcaption></figure><p>If you think climate change is only gradually affecting our natural systems, think again.</p>
<p>Our research, <a href="https://www.frontiersin.org/articles/10.3389/fmars.2019.00411/full" title="Severe continental-scale impacts of climate change are happening now: Extreme Climate Events impact marine habitat forming communities along 45% of Australia’s coast">published yesterday in Frontiers in Marine Science</a>, looked at the large-scale impacts of a series of extreme climate events on coastal marine habitats around Australia.</p>
<p>We found more than 45% of the coastline was already affected by extreme weather events caused by climate change. What’s more, these ecosystems are struggling to recover as extreme events are expected to get worse.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/40-years-ago-scientists-predicted-climate-change-and-hey-they-were-right-120502">40 years ago, scientists predicted climate change. And hey, they were right</a>
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<p>There is <a href="https://www.science.org.au/learning/general-audience/science-climate-change/5-how-are-extreme-events-changing">growing scientific evidence</a> that heatwaves, floods, droughts and cyclones are increasing in frequency and intensity, and that this is caused by climate change.</p>
<h2>Life on the coastline</h2>
<p>Corals, seagrass, mangroves and kelp are some of the key habitat-forming species of our coastline, as they all support a host of marine invertebrates, fish, sea turtles and marine mammals.</p>
<p>Our team decided to look at the cumulative impacts of recently reported extreme climate events on marine habitats around Australia. We reviewed the period between 2011 and 2017 and found these events have had devastating impacts on key marine habitats.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/285438/original/file-20190724-110187-1mum0aa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/285438/original/file-20190724-110187-1mum0aa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/285438/original/file-20190724-110187-1mum0aa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=225&fit=crop&dpr=1 600w, https://images.theconversation.com/files/285438/original/file-20190724-110187-1mum0aa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=225&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/285438/original/file-20190724-110187-1mum0aa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=225&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/285438/original/file-20190724-110187-1mum0aa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=283&fit=crop&dpr=1 754w, https://images.theconversation.com/files/285438/original/file-20190724-110187-1mum0aa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=283&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/285438/original/file-20190724-110187-1mum0aa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=283&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Healthy kelp (left) in Western Australia is an important part of the food chain but it is vulnerable to even small changes in temperature and particularly slow to recover from disturbances such as the marine heatwave of 2011. Even small patches or gaps (right) where kelp has died can take many years to recover.</span>
<span class="attribution"><span class="source">Russ Babcock</span>, <span class="license">Author provided</span></span>
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<p>These include kelp and mangrove forests, seagrass meadows, and coral reefs, some of which have not yet recovered, and may never do so. These findings paint a bleak picture, underscoring the need for urgent action.</p>
<p>During this period, which spanned both <a href="https://theconversation.com/explainer-el-nino-and-la-nina-27719">El Niño and La Niña</a> conditions, scientists around Australia reported the following events:</p>
<p><strong>2011:</strong> The <a href="https://theconversation.com/marine-heatwaves-threaten-the-future-of-underwater-forests-37154">most extreme marine heatwave ever</a> occurred off the west coast of Australia. Temperatures were as much as 2-4°C above average for extended periods and there was coral bleaching along more than 1,000km of coast and <a href="https://theconversation.com/a-marine-heatwave-has-wiped-out-a-swathe-of-was-undersea-kelp-forest-62042">loss of kelp forest along hundreds of kilometres</a>. </p>
<p>Seagrasses in <a href="https://theconversation.com/climate-change-threatens-western-australias-iconic-shark-bay-32428">Shark Bay</a> and along the entire east coast of Queensland were also severely affected by extreme flooding and cyclones. The <a href="http://www.seagrasswatch.org/Info_centre/Publications/pdf/2014/Inshore-Seagrass-Monitoring-Report-2012.pdf">loss of seagrasses in Queensland</a> may have led to a spike in <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0094849" title="Mortality of Inshore Marine Mammals in Eastern Australia Is Predicted by Freshwater Discharge and Air Temperature">deaths of turtles and dugongs</a>.</p>
<p><strong>2013:</strong> <a href="https://link.springer.com/article/10.1007/s00227-016-2956-1" title="Temporal patterns of coral cover in the offshore Pilbara, Western Australia">Extensive coral bleaching</a> took place along more than 300km of the Pilbara coast of northwestern Australia.</p>
<p><strong>2016:</strong> The most <a href="https://www.nature.com/articles/nature21707" title="Global warming and recurrent mass bleaching of corals">extreme coral bleaching ever recorded on the Great Barrier Reef</a> affected more than 1,000km of the northern Great Barrier Reef. <a href="https://theconversation.com/extreme-weather-likely-behind-worst-recorded-mangrove-dieback-in-northern-australia-71880">Mangrove forests</a> across northern Australia were killed by a combination of drought, heat and abnormally low sea levels along the coast of the Gulf of Carpentaria across the Northern Territory and into Western Australia.</p>
<p><strong>2017:</strong> An unprecedented <a href="https://www.nature.com/articles/s41558-018-0351-2" title="Ecological memory modifies the cumulative impact of recurrent climate extremes">second consecutive summer of coral bleaching on the Great Barrier Reef</a> affects northern Great Barrier Reef again, as well as parts of the reef further to the south.</p>
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<h2>Heritage areas affected</h2>
<p>Many of the impacted areas are globally significant for their size and biodiversity, and because until now they have been relatively undisturbed by climate change. Some of the areas affected are also World Heritage Areas (<a href="https://whc.unesco.org/en/list/154">Great Barrier Reef</a>, <a href="https://whc.unesco.org/en/list/578">Shark Bay</a>, <a href="https://whc.unesco.org/en/list/1369">Ningaloo Coast</a>).</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/285437/original/file-20190724-110170-11j56w3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/285437/original/file-20190724-110170-11j56w3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=225&fit=crop&dpr=1 600w, https://images.theconversation.com/files/285437/original/file-20190724-110170-11j56w3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=225&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/285437/original/file-20190724-110170-11j56w3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=225&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/285437/original/file-20190724-110170-11j56w3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=283&fit=crop&dpr=1 754w, https://images.theconversation.com/files/285437/original/file-20190724-110170-11j56w3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=283&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/285437/original/file-20190724-110170-11j56w3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=283&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Seagrass meadows in Shark Bay are among the world’s most lush and extensive and help lock large amounts of carbon into sediments. The left image shows healthy seagrass but the right image shows damage from extreme climate events in 2011.</span>
<span class="attribution"><span class="source">Mat Vanderklift</span>, <span class="license">Author provided</span></span>
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<p>The habitats affected are “foundational”: they provide food and shelter to a huge range of species. Many of the animals affected – such as large fish and turtles – support commercial industries such as tourism and fishing, as well as being culturally important to Australians.</p>
<p>Recovery across these impacted habitats has begun, but it’s likely some areas will never return to their previous condition. </p>
<p>We have used ecosystem models to evaluate the likely long-term outcomes from extreme climate events <a href="https://theconversation.com/marine-heatwaves-are-getting-hotter-lasting-longer-and-doing-more-damage-95637">predicted to become more frequent and more intense</a>. </p>
<p>This work suggests that even in places where recovery starts, the average time for full recovery may be around 15 years. Large slow-growing species such as sharks and dugongs could take even longer, up to 60 years. </p>
<p>But extreme climate events are predicted to occur less than 15 years apart. This will result in a step-by-step decline in the condition of these ecosystems, as it leaves too little time between events for full recovery.</p>
<p>This already appears to be happening with the corals of the Great Barrier Reef.</p>
<h2>Gradual decline as things get warmer</h2>
<p>Damage from extreme climate events occurs on top of more gradual changes driven by increases in average temperature, such as loss of kelp forests on the southeast coasts of Australia due to the <a href="http://www.fish.gov.au/reports/Documents/2014_refs/29.%20Johnson_and_Friends%20JEMBE%202011.pdf" title="Climate change cascades: Shifts in oceanography, species' ranges and subtidal marine community dynamics in eastern Tasmania">spread of sea urchins</a> and <a href="https://www.pnas.org/content/113/48/13791" title="Long-term empirical evidence of ocean warming leading to tropicalization of fish communities, increased herbivory, and loss of kelp">tropical grazing fish species</a>.</p>
<p>Ultimately, we need to slow down and stop the heating of our planet due to the release of greenhouse gases. But even with immediate and effective emissions reduction, the planet will remain warmer, and extreme climatic events more prevalent, for decades to come.</p>
<p>Recovery might still be possible, but we need to know more about recovery rates and what factors promote recovery. This information will allow us to give the ecosystems a helping hand through active restoration and rehabilitation efforts.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/more-than-28-000-species-are-officially-threatened-with-more-likely-to-come-120430">More than 28,000 species are officially threatened, with more likely to come</a>
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<p>We will need new ways to help ecosystems function and to deliver the services that we all depend on. This will likely include decreasing (or ideally, stopping) direct human impacts, and actively assisting recovery and restoring damaged ecosystems. </p>
<p>Several such programs are active around Australia and internationally, attempting to boost the ability of <a href="https://www.csiro.au/en/Research/OandA/Areas/Coastal-management/Reef-capability/Coral-spawn-harvesting">corals</a>, <a href="https://seagrassrestoration.net/">seagrass</a>, <a href="https://www.iucn.org/theme/forests/our-work/forest-landscape-restoration/mangrove-restoration">mangroves</a> and <a href="http://www.operationcrayweed.com/">kelp</a> to recover.</p>
<p>But they will need to be massively scaled up to be effective in the context of the large scale disturbances seen in this decade.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/285441/original/file-20190724-110158-ddxv69.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/285441/original/file-20190724-110158-ddxv69.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/285441/original/file-20190724-110158-ddxv69.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=225&fit=crop&dpr=1 600w, https://images.theconversation.com/files/285441/original/file-20190724-110158-ddxv69.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=225&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/285441/original/file-20190724-110158-ddxv69.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=225&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/285441/original/file-20190724-110158-ddxv69.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=283&fit=crop&dpr=1 754w, https://images.theconversation.com/files/285441/original/file-20190724-110158-ddxv69.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=283&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/285441/original/file-20190724-110158-ddxv69.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=283&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Mangroves at the Flinders River near Karumba in the Gulf of Carpentaria. The healthy mangrove forest (left) is near the river while the dead mangroves (right) are at higher levels where they were much more stressed by conditions in 2016. Some small surviving mangroves are seen beginning to recover by 2017.</span>
<span class="attribution"><span class="source">Robert Kenyon</span>, <span class="license">Author provided</span></span>
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</figure><img src="https://counter.theconversation.com/content/120671/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Russ Babcock; currently receiving funding from CSIRO, DoEE, BHP, GBRF. </span></em></p><p class="fine-print"><em><span>Anthony Richardson receives funding from the Australian Research Council and the Commonwealth Department of Education (NCRIS)</span></em></p><p class="fine-print"><em><span>Beth Fulton receives funding from CSIRO, AFMA, FRDC, Lenfest Oceans Programme, FAO, the Canadian and Norwegian governments. Beth is also a Pew Marine Fellow.</span></em></p><p class="fine-print"><em><span>Eva Plaganyi receives funding from CSIRO, AFMA, FRDC </span></em></p><p class="fine-print"><em><span>Rodrigo Bustamante receives funding from CSIRO </span></em></p>Corals, mangroves and seagrass habitats have been affected by extreme weather events, and some may never recover.Russ Babcock, Senior Principal Research Scientist, CSIROAnthony Richardson, Professor, The University of QueenslandBeth Fulton, CSIRO Research Group Leader Ecosystem Modelling and Risk Assessment, CSIROÉva Plagányi, Senior Principal Research Scientist, CSIRORodrigo Bustamante, Research Group Leader , CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1118922019-05-15T10:46:24Z2019-05-15T10:46:24ZRetired oil rigs off the California coast could find new lives as artificial reefs<figure><img src="https://images.theconversation.com/files/274452/original/file-20190514-60532-1ts62c4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A school of juvenile bocaccio in the midwaters of Platform Gilda, Santa Barbara Channel, Calif.</span> <span class="attribution"><span class="source">Scott Gietler</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Offshore oil and gas drilling has been a contentious issue in California for 50 years, ever since a rig ruptured and spilled <a href="https://theconversation.com/trumps-push-for-new-offshore-drilling-is-likely-to-run-aground-in-california-89952">80,000 to 100,000 barrels of crude oil</a> off Santa Barbara in 1969. Today it’s spurring a new debate: whether to completely dismantle 27 oil and gas platforms scattered along the southern California coast as they end their working lives, or convert the underwater sections into permanent artificial reefs for marine life.</p>
<p>We know that here and elsewhere, many thousands of fishes and millions of invertebrates use offshore rigs as marine habitat. Working with state fisheries agencies, energy companies have converted decommissioned oil and gas platforms into manmade reefs in the U.S. Gulf of Mexico, Brunei and Malaysia. </p>
<p>Californians <a href="https://theconversation.com/coastal-protection-on-the-edge-the-challenge-of-preserving-californias-legacy-76927">prize their spectacular coastline</a>, and there are <a href="https://www.eenews.net/stories/1060034680">disagreements over the rigs-to-reefs concept</a>. Some conservation groups assert that abandoned oil rigs could <a href="https://www.surfrider.org/coastal-blog/entry/rigs-to-grief-a-bad-oil-bill-stopped">release toxic chemicals into the water</a> and create underwater hazards. In contrast, supporters say the submerged sections have become <a href="https://www.change.org/p/support-the-rigs-to-reefs-program-in-california">productive reefs that should be left in place</a>.</p>
<p>We are a <a href="https://scholar.google.com/citations?user=nWPT_lEAAAAJ&hl=en">former research scientist for the U.S. Department of the Interior</a> and a scholar focusing on the <a href="https://scholar.google.com/scholar?hl=en&as_sdt=0%2C22&q=MS+Love&btnG=">fishes of the Pacific coast</a>. In a recent study, we reviewed the history of rigs-to-reefs conversions and decades of published scientific research monitoring the <a href="https://doi.org/10.1016/j.ocecoaman.2018.10.024">effects of these projects</a>. Based on this record, we conclude that reefing the habitat under decommissioned oil and gas platforms is a viable option for California. It also could serve as a model for decommissioning some of the 7,500 other offshore platforms operating around the world.</p>
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<figcaption><span class="caption">Reefing oil rigs clearly benefits oil companies, but scientists say it’s also good for marine life.</span></figcaption>
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<h2>Unplanned underwater communities</h2>
<p>Offshore petroleum platforms are designed to withstand hurricanes and earthquakes, but not to be permanent. When they reach the end of their useful lives, typically after about 25 to 50 years of operation, federal and state law require energy companies to decommission them. </p>
<p>This usually means completely removing the platform and submerged supporting structure and returning the seafloor to an unobstructed condition. Only in certain cases does any part of the platform remain. </p>
<p>These rigs weren’t designed with the intent of creating reefs, but their underwater steel pipe support systems – called “jackets” in the oil business – attract vast numbers of invertebrates that settle on them. In turn, these creatures attract diverse fish species. Together these colonies create reef systems that can resist rusting away for several hundred years. </p>
<p>Off California, a myriad of invertebrates coat each platform jacket. Millions of mussels, sea stars and brightly colored anemones fight for space, creating a quilt of patterns and textures. Both large and small fishes are also abundant. In some years, clouds of hundreds of thousands of juvenile rockfishes school in the depths below operating oil platforms.</p>
<h2>Creating new habitat</h2>
<p>Humans have sought to enhance fisheries with artificial reefs for centuries, using materials ranging from wood, rock and concrete to <a href="https://oceanservice.noaa.gov/facts/artificial-reef.html">decommissioned ships</a>. The idea of reefing platform jackets developed after oil and gas companies started building platforms in the Gulf of Mexico in the late 1940s. Those steel-pipe structures provided rock-hard habitat for reef fishes on an otherwise smooth seafloor, and became highly popular fishing destinations. </p>
<p>Installing thousands of platforms catalyzed a basin-wide increase in available reef fish species, such as the highly prized red snapper. Reef fishes moved into areas where they had previously been scarce due to a <a href="https://cil.nus.edu.sg/wp-content/uploads/2013/06/11.-Prof.-Richard-MCLAUGHLIN-_Idle-Iron_-versus-_Rigs-to-Reefs_-Surviving-Conflicting-Policy-Mandates-in-the-Gulf-of-Mexico.pdf">lack of hard habitat</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/274455/original/file-20190514-60537-r0oun4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/274455/original/file-20190514-60537-r0oun4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/274455/original/file-20190514-60537-r0oun4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/274455/original/file-20190514-60537-r0oun4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/274455/original/file-20190514-60537-r0oun4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/274455/original/file-20190514-60537-r0oun4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/274455/original/file-20190514-60537-r0oun4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/274455/original/file-20190514-60537-r0oun4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A marine biologist surveys fishes living at Platform A, Santa Barbara Channel, Calif.</span>
<span class="attribution"><span class="source">Desmond Ho</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>In the mid-1980s Louisiana legislated the <a href="http://www.wlf.louisiana.gov/fishing/artificial-reef-program">first U.S. reefing option</a> for its offshore waters. This program was designed to take advantage of fishing opportunities provided by obsolete platforms and encourage energy companies to convert decommissioned platforms into reefs. Since then, over 500 submerged jackets in the Gulf, from Texas to Alabama, have been adapted into state artificial reef programs. </p>
<p>Platforms generally consist of two distinct parts: the topside, or operational facilities seen above water, and the substructure, or parts below the water. To make a reef, energy companies completely remove the topside and transfer it to shore for recycling or partial reuse. In the Gulf of Mexico and elsewhere, they may tow the underwater jacket to a new location; topple it onto the seabed; or cut off the top portion and <a href="https://www.bsee.gov/what-we-do/environmental-focuses/rigs-to-reefs#3">place it on the seabed next to the lower portion</a>.</p>
<p>California law only allows partial removal, or cutting off of the top portion. That way the underwater jacket remains intact and in place, which is the least destructive method for the reef. </p>
<h2>Helping or hurting sea life?</h2>
<p>Across the Gulf of Mexico, reefed oil platforms have significantly increased the amount of available reef fish. Many have become popular <a href="https://www.saltstrong.com/articles/texas-fishing-reef-gps-coordinates/">fishing</a> and <a href="https://www.smithsonianmag.com/travel/gulf-mexicos-hottest-diving-spots-are-decommissioned-oil-rigs-180971728/">scuba diving</a> sites. In California most operating platforms are not fished, so they have functioned for decades as de facto Marine Protected Areas, providing ecological benefits for severely overfished species. </p>
<p>For example, scientists have found greater numbers of adult fish of some species, such as cowcod and bocaccio rockfishes, under platforms than on natural reefs. More adults capable of spawning makes it likely that more larvae will be released into the ecosystem from species under platforms than from smaller numbers on nearby natural areas that are fished. </p>
<p>Although some platforms have been installed and removed off of southern California, none have been reefed. Discussion of reefing, supported by many years of scientific studies in California waters, led to enactment of the <a href="https://law.justia.com/codes/california/2016/code-fgc/division-6/part-1/chapter-5.5/article-2/">2010 Marine Resources Legacy Act</a>, which authorized the rigs-to-reefs concept. Now Platform Holly in state waters and Platforms Grace, Gail, Hermosa, Hildago and Harvest in federal waters are undergoing initial steps for decommissioning. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/273883/original/file-20190510-183080-1eg1enr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273883/original/file-20190510-183080-1eg1enr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273883/original/file-20190510-183080-1eg1enr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=458&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273883/original/file-20190510-183080-1eg1enr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=458&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273883/original/file-20190510-183080-1eg1enr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=458&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273883/original/file-20190510-183080-1eg1enr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=576&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273883/original/file-20190510-183080-1eg1enr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=576&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273883/original/file-20190510-183080-1eg1enr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=576&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Platform Holly in California’s Santa Barbara Channel is one of the rigs scheduled for near-term decommissioning.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/California-Offshore-Oil/b218a544ab204cb7bb8bf78ddedd7238/1/0">State Lands Commission via AP</a></span>
</figcaption>
</figure>
<p>This process is expensive, technically complex and lengthy. Because it requires intricate planning, oil companies are likely to consider decommissioning more platforms while they are already organizing equipment, engineering and infrastructure acquisition for the current set. Although industry will save money if a platform is reefed, the savings must be shared with the state. Reefing thus could generate funds for other marine conservation efforts.</p>
<p>Either total or partial decommissioning will have many environmental and socioeconomic impacts, both positive and negative. Californians have not had an opportunity to consider what should happen to decommissioned oil platforms since the mid-1990s. Now citizens have an opportunity to consider the issues again, and decide the fate of an unintended but biologically important resource.</p><img src="https://counter.theconversation.com/content/111892/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ann Scarborough Bull received funding for the study described in this article from ExxonMobil Upstream Research.</span></em></p><p class="fine-print"><em><span>Milton Love received research funding for the study described in this article from ExxonMobil Upstream Research, and has received grants from numerous government agencies and foundations.</span></em></p>Californians love their coast and strongly oppose offshore drilling. Will they support converting old oil rigs to artificial reefs – a policy that benefits both marine life and oil companies?Ann Scarborough Bull, Visiting Researcher, Marine Science institute, University of California, Santa BarbaraMilton Love, Research Biologist, Marine Science Institute, University of California, Santa BarbaraLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1128392019-03-04T19:02:23Z2019-03-04T19:02:23ZSuffering in the heat: the rise in marine heatwaves is harming ocean species<figure><img src="https://images.theconversation.com/files/261770/original/file-20190303-110119-1w5b8am.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Recent marine heatwaves have devastated crucial coastal habitats, including kelp forests, seagrass meadows and coral reefs.</span> <span class="attribution"><span class="source">Dan Smale</span>, <span class="license">Author provided</span></span></figcaption></figure><p>In the midst of a raging heatwave, most people think of the ocean as a nice place to cool down. But heatwaves can strike in the ocean as well as on land. And when they do, marine organisms of all kinds – plankton, seaweed, corals, snails, fish, birds and mammals – also feel the wrath of soaring temperatures.</p>
<p>Our new research, <a href="https://www.nature.com/articles/s41558-019-0412-1">published today in Nature Climate Change</a>, makes abundantly clear the destructive force of marine heatwaves. We compared the effects on ecosystems of eight marine heatwaves from around the world, including four El Niño events (1982-83, 1986-87, 1991-92, 1997-98), three extreme heat events in the Mediterranean Sea (1999, 2003, 2006) and one in <a href="https://theconversation.com/a-marine-heatwave-has-wiped-out-a-swathe-of-was-undersea-kelp-forest-62042">Western Australia in 2011</a>. We found that these events can significantly damage the health of corals, kelps and seagrasses.</p>
<p>This is concerning, because these species form the foundation of many ecosystems, from the tropics to polar waters. Thousands of other species – not to mention a wealth of human activities – depend on them.</p>
<p>We identified southeastern Australia, southeast Asia, northwestern Africa, Europe and eastern Canada as the places where marine species are most at risk of extreme heat in the future.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/marine-heatwaves-are-getting-hotter-lasting-longer-and-doing-more-damage-95637">Marine heatwaves are getting hotter, lasting longer and doing more damage</a>
</strong>
</em>
</p>
<hr>
<p>Marine heatwaves are defined as periods of five days or more during which ocean temperatures are unusually high, compared with the long-term average for any given place. Just like their counterparts on land, marine heatwaves have been getting <a href="https://theconversation.com/marine-heatwaves-are-getting-hotter-lasting-longer-and-doing-more-damage-95637">more frequent, hotter and longer</a> in recent decades. Globally, there were 54% more heatwave days per year between 1987 and 2016 than in 1925–54.</p>
<p>Although the heatwaves we studied varied widely in their maximum intensity and duration, we found that all of them had negative impacts on a broad range of different types of marine species.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/261771/original/file-20190303-110140-mhsu67.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/261771/original/file-20190303-110140-mhsu67.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/261771/original/file-20190303-110140-mhsu67.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/261771/original/file-20190303-110140-mhsu67.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/261771/original/file-20190303-110140-mhsu67.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/261771/original/file-20190303-110140-mhsu67.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/261771/original/file-20190303-110140-mhsu67.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Marine heatwaves in tropical regions have caused widespread coral bleaching.</span>
</figcaption>
</figure>
<p>Humans also depend on these species, either directly or indirectly, because they underpin a wealth of ecological goods and services. For example, many marine ecosystems support commercial and recreational fisheries, contribute to carbon storage and nutrient cycling, offer venues for tourism and recreation, or are culturally or scientifically significant.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/australias-other-reef-is-worth-more-than-10-billion-a-year-but-have-you-heard-of-it-45600">Australia's 'other' reef is worth more than $10 billion a year - but have you heard of it?</a>
</strong>
</em>
</p>
<hr>
<p>.</p>
<p>Marine heatwaves have had negative impacts on virtually all these “ecosystem services”. For example, seagrass meadows in the Mediterranean Sea, which store significant amounts of carbon, are harmed by extreme temperatures recorded during marine heatwaves. In the summers of both 2003 and 2006, marine heatwaves led to widespread seagrass deaths. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/seagrass-protector-of-shipwrecks-and-buried-treasure-103364">Seagrass, protector of shipwrecks and buried treasure</a>
</strong>
</em>
</p>
<hr>
<p>The marine heatwaves off the west coast of Australia in 2011 and northeast America in 2012 led to dramatic changes in the regionally important abalone and lobster fisheries, respectively. Several marine heatwaves associated with El Niño events caused widespread coral bleaching with consequences for biodiversity, fisheries, coastal erosion and tourism. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/261772/original/file-20190303-110123-iacfvu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/261772/original/file-20190303-110123-iacfvu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=518&fit=crop&dpr=1 600w, https://images.theconversation.com/files/261772/original/file-20190303-110123-iacfvu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=518&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/261772/original/file-20190303-110123-iacfvu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=518&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/261772/original/file-20190303-110123-iacfvu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=651&fit=crop&dpr=1 754w, https://images.theconversation.com/files/261772/original/file-20190303-110123-iacfvu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=651&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/261772/original/file-20190303-110123-iacfvu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=651&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Mass die-offs of finfish and shellfish have been recorded during marine heatwaves, with major consequences for regional fishing industries.</span>
</figcaption>
</figure>
<p>All evidence suggests that <a href="https://www.nature.com/articles/ncomms16101">marine heatwaves are linked to human mediated climate change</a> and will continue to intensify with ongoing global warming. The impacts can only be minimised by combining rapid, meaningful reductions in greenhouse emissions with a more adaptable and pragmatic approach to the management of marine ecosystems.</p><img src="https://counter.theconversation.com/content/112839/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dan Smale receives funding from the Natural Environment Research Council (UK). </span></em></p><p class="fine-print"><em><span>Thomas Wernberg receives funding from The Australian Research Council. </span></em></p>Marine heatwaves, like their land counterparts, are growing hotter and longer. Sea species in southeastern Australia, southeast Asia, northwestern Africa, Europe and eastern Canada are most at risk.Dan Smale, Research Fellow in Marine Ecology, Marine Biological AssociationThomas Wernberg, Associate professor, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1089862018-12-18T19:13:59Z2018-12-18T19:13:59ZExploring Australia’s ‘other reefs’ south of Tasmania<figure><img src="https://images.theconversation.com/files/251125/original/file-20181217-27779-1tg4cyr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Solenosmilia coral reef with unidentified solitary yellow corals.</span> <span class="attribution"><span class="source">CSIRO</span></span></figcaption></figure><p>Off southern Tasmania, at depths between 700 and 1,500 metres, more than 100 undersea mountains provide rocky pedestals for deep-sea coral reefs.</p>
<p>Unlike shallow tropical corals, deep-sea corals live in a cold environment without sunlight or symbiotic algae. They feed on tiny organisms filtered from passing currents, and protect an assortment of other animals in their intricate structures.</p>
<p>Deep-sea corals are fragile and slow-growing, and vulnerable to human activities such as fishing, mining and climate-related changes in ocean temperatures and acidity.</p>
<p>This week we returned from a month-long research voyage on CSIRO vessel <em>Investigator</em>, part of Australia’s Marine National Facility. We criss-crossed many seamounts in and near the Huon and Tasman Fracture marine parks, which are home to both pristine and previously fished coral reefs. These two parks are part of a larger network of Australian Marine Parks that surround Australia’s coastline and protect our offshore marine environment.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/251126/original/file-20181218-27776-x0p4qp.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/251126/original/file-20181218-27776-x0p4qp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/251126/original/file-20181218-27776-x0p4qp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=373&fit=crop&dpr=1 600w, https://images.theconversation.com/files/251126/original/file-20181218-27776-x0p4qp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=373&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/251126/original/file-20181218-27776-x0p4qp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=373&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/251126/original/file-20181218-27776-x0p4qp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=469&fit=crop&dpr=1 754w, https://images.theconversation.com/files/251126/original/file-20181218-27776-x0p4qp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=469&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/251126/original/file-20181218-27776-x0p4qp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=469&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The RV Investigator criss-crossed the Huon and Tasman Fracture marine parks.</span>
<span class="attribution"><span class="source">CSIRO</span></span>
</figcaption>
</figure>
<p>The data we collected will answer our two key research questions: what grows where in these environments, and are corals regrowing after more than 20 years of protection?</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-the-rv-investigators-role-in-marine-science-35239">Explainer: the RV Investigator’s role in marine science</a>
</strong>
</em>
</p>
<hr>
<h2>Our eyes on the seafloor</h2>
<p>Conducting research in rugged, remote deep-sea environments is expensive and technically challenging. It’s been a test of patience and ingenuity for the 40 ecologists, technicians and marine park managers on board, and the crew who provide electronics, computing and mechanical support.</p>
<p>But now, after four weeks of working around-the-clock shifts, we’re back in the port of Hobart. We have completed 147 transects covering more 200 kilometres in length and amassed more than 60,000 stereo images and some 300 hours of video for analysis.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/251127/original/file-20181218-27752-18i8j3r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/251127/original/file-20181218-27752-18i8j3r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/251127/original/file-20181218-27752-18i8j3r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/251127/original/file-20181218-27752-18i8j3r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/251127/original/file-20181218-27752-18i8j3r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/251127/original/file-20181218-27752-18i8j3r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/251127/original/file-20181218-27752-18i8j3r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/251127/original/file-20181218-27752-18i8j3r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The deep tow camera system weighs 350 kilos and has four cameras, four lights and a control unit encased in high-strength aluminium housings.</span>
<span class="attribution"><span class="source">CSIRO</span></span>
</figcaption>
</figure>
<p>A deep-tow camera system designed and built by CSIRO was our eye on the seafloor. This 350 kilogram system has four cameras, four lights and a control unit encased in high-strength aluminium housings.</p>
<p>An operations planner plots “flight-paths” down the seamounts, adding a one-kilometre run up for the vessel skipper to land the camera on each peak. The skipper navigates swell, wind and current to ensure a steady course for each one-hour transect.</p>
<p>An armoured fibre optic tow cable relays high-quality, real-time video back to the ship. This enables the camera “pilot” in the operations room to manoeuvre the camera system using a small joystick, and keep the view in focus, a mere two metres off the seafloor.</p>
<p>This is an often challenging job, as obstacles like large boulders or sheer rock walls loom out of the darkness with little warning. The greatest rapid ascent, a near-vertical cliff 45m in height, resulted in highly elevated blood pressure and one broken camera light!</p>
<h2>Reaching into their world</h2>
<p>Live imagery from the camera system was compelling. As well as the main reef-building stony coral <em>Solenosmilia variabilis</em>, we saw hundreds of other animals including feathery solitary soft corals, tulip-shaped glass sponges and crinoids. Their colours ranged from delicate creams and pinks to striking purples, bright yellows and golds.</p>
<p>To understand the make-up of coral communities glimpsed by our cameras, we also used a small net to sample the seafloor animals for identification. For several of the museum taxonomists onboard, this was their first contact with coral and mollusc species they had known, and even named, only from preserved specimens.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/251165/original/file-20181218-27749-186e3ah.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/251165/original/file-20181218-27749-186e3ah.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/251165/original/file-20181218-27749-186e3ah.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=323&fit=crop&dpr=1 600w, https://images.theconversation.com/files/251165/original/file-20181218-27749-186e3ah.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=323&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/251165/original/file-20181218-27749-186e3ah.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=323&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/251165/original/file-20181218-27749-186e3ah.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=406&fit=crop&dpr=1 754w, https://images.theconversation.com/files/251165/original/file-20181218-27749-186e3ah.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=406&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/251165/original/file-20181218-27749-186e3ah.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=406&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A deepwater hippolytid shrimp with large hooked claw, which it uses to clean coral and get food.</span>
<span class="attribution"><span class="source">CSIRO</span></span>
</figcaption>
</figure>
<p>We found a raft of undescribed species, as expected in such remote environments. In many cases this is likely to be the only time these species are ever collected. We also found animals living among the corals, hinting at their complex interdependencies. This included brittlestars curled around corals, polychaete worms tunnelling inside corals, and corals growing on shells.</p>
<p>We used an oceanographic profiler to sample the chemical properties of the water to 2,000m. Although further analysis is required, our aim here is to see whether long-term climate change is impacting the living conditions at these depths.</p>
<p>A curious feature of one of the southern seamounts is that it hosts the world’s only known aggregation of deep-water eels. We have sampled these eels twice before and were keen to learn more about this rare phenomenon.</p>
<p>Using an electric big-game fishing rig we landed two egg-laden female eels from a depth of 1,100 metres: a possible first for the record books.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/251129/original/file-20181218-27776-nx1qei.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/251129/original/file-20181218-27776-nx1qei.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/251129/original/file-20181218-27776-nx1qei.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/251129/original/file-20181218-27776-nx1qei.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/251129/original/file-20181218-27776-nx1qei.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/251129/original/file-20181218-27776-nx1qei.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/251129/original/file-20181218-27776-nx1qei.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/251129/original/file-20181218-27776-nx1qei.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Dave Logan of Parks Australia with an eel landed from more than a kilometre under the sea.</span>
<span class="attribution"><span class="source">Fraser Johnston/CSIRO</span></span>
</figcaption>
</figure>
<p>In a side-project, a team of observers recorded 42 seabird species and eight whale and dolphin species. They have one more set of data towards completing the first circum-Australia survey of marine birds and mammals.</p>
<h2>More coral pedestals than we realise</h2>
<p>An important finding was that living <em>S. variabilis</em> reefs extended between the seamounts on raised ridges down to about 1,450m. This means there is more of this important coral matrix in the Huon and Tasman Fracture marine parks than we previously realised.</p>
<p>In areas that were revisited to assess the regrowth of corals after two decades of protection from fishing, we saw no evidence that the coral communities are recovering. But there were signs that some individual species of corals, featherstars and urchins have re-established a foothold.</p>
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Read more:
<a href="https://theconversation.com/sludge-snags-and-surreal-animals-life-aboard-a-voyage-to-study-the-abyss-79924">Sludge, snags, and surreal animals: life aboard a voyage to study the abyss</a>
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<p>In coming months we will work through a sub-sample of our deep-sea image library to identify the number and type of organisms in certain areas. This will give us a clear, quantitative picture of where and at what depth different species and communities live in these marine parks, and a foundation for predicting their likely occurrence both in Australia and around the world.</p>
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<p><em>The seamount corals survey involved 10 organisations: CSIRO, the National Environmental Science Program Marine Biodiversity Hub, Australian Museum, Museums Victoria, Tasmanian Museum and Art Gallery, NIWA (NZ), three Australian universities and Parks Australia.</em></p><img src="https://counter.theconversation.com/content/108986/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nic Bax receives funding from CSIRO and the Australian Government National Environmental Science Program, Marine Biodiversity Hub </span></em></p><p class="fine-print"><em><span>Alan Williams receives funding from CSIRO, NESP Biodiversity Hub, Parks Australia
</span></em></p>In the cold southern oceans, underwater mountains support deep-sea reefs.Nic Bax, Director, NERP Marine Biodiversity Hub, CSIROAlan Williams, Researcher, CSIROLicensed as Creative Commons – attribution, no derivatives.