tag:theconversation.com,2011:/fr/topics/coral-reefs-5182/articlesCoral reefs – The 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>
<figcaption>
<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>
<figcaption>
<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>
</figcaption>
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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>
</figure>
<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/2249942024-03-19T19:16:59Z2024-03-19T19:16:59ZRestoring reefs killed by climate change may simply put corals ‘back out to die’ – here’s how we can improve their chances<figure><img src="https://images.theconversation.com/files/582810/original/file-20240319-18-tghi99.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4980%2C3317&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Coral bleaching in a shallow lagoon of French Polynesia.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/coral-bleaching-pocillopora-bleached-due-el-419544157">Damsea/Shutterstock</a></span></figcaption></figure><p>Coral reefs, like sprawling cities of the sea, support an estimated <a href="https://www.sciencedirect.com/science/article/pii/S0960982214016236">25%</a> of all plants and animals in the ocean. Worldwide, <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.16391">1 billion people</a> depend on these ecosystems for food, income and coastal protection. </p>
<p>Unfortunately, coral reefs are dogged with endless sources of stress, from climate change and pollution to overfishing and unsustainable coastal development. The outlook for corals and the reefs they build is not good: without drastic action on greenhouse gas emissions scientists predict that conditions in tropical coastal waters will become <a href="https://journals.plos.org/climate/article?id=10.1371/journal.pclm.0000004">inhospitable to corals by the year 2100</a>. If we want coral reefs in our future, we need to be proactive.</p>
<p>Scientists, conservationists and local communities are working to recover unhealthy reefs. There are many options for doing this: encouraging <a href="https://theconversation.com/coral-sex-how-reproducing-species-in-the-lab-could-be-key-to-restoring-reefs-in-the-wild-143776">coral sex in the lab</a> to produce enormous batches of coral larvae that can be released into the wild, for example, or selectively breeding and genetically engineering specimens to create stress-resistant “<a href="https://theconversation.com/heat-tolerant-corals-can-create-nurseries-that-are-resistant-to-bleaching-116675">super corals</a>”. </p>
<p>Although coral restoration has become a <a href="https://www.icriforum.org/wp-content/uploads/2021/11/Hein-Staub-2021-Mapping-the-Global-Funding-Landscape-for-Coral-Reef-Restoration-ICRI-WEB.pdf">multi-million dollar business</a>, many restoration projects fail to transform the ecosystem’s long-term <a href="https://esajournals.onlinelibrary.wiley.com/doi/10.1002/fee.2471">prospects</a>, wasting time and resources and raising questions about the ethics of <a href="https://www.science.org/content/article/after-mass-coral-die-off-florida-scientists-rethink-plan-to-save-ailing-reefs?utm_source=sfmc&amp;utm_medium=email&amp;utm_content=alert&amp;utm_campaign=SCIeToc&amp;et_rid=34982278&amp;et_cid=5094116">simply putting corals “back out to die”</a>, as Ian Enochs, a US marine biologist who heads the National Oceanic and Atmospheric Administration’s reef monitoring programme in the Atlantic Ocean and Caribbean Sea recently described it. </p>
<p>In our <a href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3002542">new paper</a>, we propose a new way of thinking about coral restoration: making environmental conditions, such as temperature and nutrient levels, the determining factor for whether reef restoration should go ahead. This might seem obvious, but our survey of academic research on coral restoration from 1984 to 2022 suggested these questions have been neglected. </p>
<h2>Reefs of tomorrow</h2>
<p>Coral restoration so far has been highly reactive. Efforts have focused on recovering reefs in areas where they have previously been, despite those reefs having recently died. When the cause of a dead reef is distinct and known, such as a one-off pollution event, this might be an appropriate response (so long as the cause of death has been removed). </p>
<p>But degraded coral reefs are more often the result of stress that is not easy to deal with, such as marine heatwaves caused by climate change or vast coastal developments. It’s no surprise that efforts to restore reefs in areas plagued by these problems often fail – the original issue is still present. </p>
<p>We think there are two ways to give coral reef restoration projects the best possible chance of success. First, when restoring corals to a reef that has died, do so with an in-depth knowledge of the area’s environmental conditions – both as they exist today and as they are expected to in future. This information can indicate which coral species are most sensible to use, how they should be grown, when to plant them in the wild and how to attach them to the seabed.</p>
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<a href="https://images.theconversation.com/files/581767/original/file-20240313-24-ymzpak.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Rows of metal poles with corals growing on them." src="https://images.theconversation.com/files/581767/original/file-20240313-24-ymzpak.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581767/original/file-20240313-24-ymzpak.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581767/original/file-20240313-24-ymzpak.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581767/original/file-20240313-24-ymzpak.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581767/original/file-20240313-24-ymzpak.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581767/original/file-20240313-24-ymzpak.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581767/original/file-20240313-24-ymzpak.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&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 nursery of young smooth cauliflower coral (<em>Stylophora pistillata</em>) that are almost ready to be transplanted in the northern Red Sea.</span>
<span class="attribution"><span class="source">H. Nativ/Morris Kahn Marine Research Station</span></span>
</figcaption>
</figure>
<p>Option two is to nurture new coral reefs in areas where they have not been historically present, but where environmental conditions in coming years and decades may be favourable. We might find these areas at the edges of where coral reefs are currently found. Other areas may emerge as the resolution of environmental monitoring improves.</p>
<h2>Go with the flow</h2>
<p>Innovation in coral restoration is evidently needed; a host of ethical, political, economic and ecological questions need addressing. It’s time to ensure these decisions are grounded in a robust bedrock of environmental knowledge – to break the restoration cycle of failure we are locked into.</p>
<p>We must recognise that, although a coral reef used to be in a particular place, it might now (or in the near future) be more effective to “restore” that reef elsewhere. Coral restoration could become more goal-oriented and forward-looking. </p>
<p>There are technical limitations to measuring environmental conditions and predicting what they will be like in future. Nevertheless, this fresh outlook allows us to work with environmental change rather than fight against it. If successful, it could help coral reef ecosystems endure for future generations to enjoy.</p>
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<p class="fine-print"><em><span>Heidi Burdett receives funding from the Vetenskapsrådet (Swedish Research Council) and Formas (Swedish Research Council for Sustainable Development).</span></em></p><p class="fine-print"><em><span>Gavin Foster receives funding from European Research Council (Advanced Grant #884650 Microns2Reefs). </span></em></p><p class="fine-print"><em><span>Tessa M Page receives funding from the European Research Council (Advanced 332 Grant #884650 Microns2Reefs).</span></em></p>For decades, conservationists have tried to repopulate dead reefs with corals reared elsewhere.Heidi Burdett, Associate Professor of Marine Science and Sustainability, Umeå UniversityGavin Foster, Professor of Isotope Geochemistry, University of SouthamptonTessa M Page, Research fellow, University of SouthamptonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2242842024-03-08T16:21:36Z2024-03-08T16:21:36ZRestored coral reefs can grow as fast as healthy reefs after just four years – new study<p>The coral reefs of south Sulawesi are some of the most diverse, colourful and vibrant in the world. At least, they used to be, until they were <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/rec.12866">decimated by dynamite fishing</a> in the 1990s. </p>
<p>As part of a team of coral reef ecologists based in Indonesia and the UK, we study the reefs around Pulau Bontosua, a small Indonesian island in south Sulawesi. Thirty years on, what were once large areas of thriving coral are now degraded sites are still devoid of colour, fish and other marine life. Broken skeletons of dead corals roll around on the seabed, crushing and killing any new coral larvae that try to settle and preventing the reefs from recovering naturally. </p>
<p>In many places around the world, damage like this might be described as irreparable. But at Pulau Bontosua, the story is different. Here, efforts by the <a href="https://www.buildingcoral.com/">Mars coral restoration programme</a> have brought back the coral and important ecosystem functions, as outlined by our new study, <a href="https://doi.org/10.1016/j.cub.2024.02.009">published in Current Biology</a>. We found that within just four years, restored reefs grow at the same rate as nearby healthy reefs. </p>
<p>The Mars coral restoration programme is one of the world’s largest restoration projects and has collaborated with local communities for more than a decade. Healthy coral fragments are attached to hexagonal, sand-covered steel frames called “reef stars”. These reef stars are installed on damaged reefs, where they stabilise the loose rubble, support growth of new coral and provide habitat for reef animals to move in.</p>
<h2>Speedy recovery</h2>
<p>The transplanted corals grow remarkably quickly. Within a year, fragments have developed into proper colonies. After two years, they interlock branches with their neighbours. After just four years, they completely overgrow the reef star structures and restoration sites are barely distinguishable from nearby healthy reefs.</p>
<p>The combined growth of many corals generates a complex limestone (calcium carbonate) framework. This provides habitat for marine life and protects nearby shorelines from storm damage by <a href="https://theconversation.com/coral-reefs-work-as-natures-sea-walls-it-pays-to-look-after-them-26655">absorbing up to 97% of coastal wave energy</a>. </p>
<p>We measured the overall growth of the reef framework by calculating its <a href="https://www.exeter.ac.uk/research/projects/geography/reefbudget/">carbonate budget</a>. That’s the balance between limestone production (by calcifying corals and coralline algae) and erosion (by grazing sea urchins and fishes, for example). A healthy reef produces up to 20kg reef structure per square metre per year, while a degraded reef is shrinking rather than growing, as erosion exceeds limestone production. Therefore, overall reef growth gives an indication of reef health.</p>
<p>At Pulau Bontosua, our survey data shows that in the years following restoration, coral cover, coral colony sizes and carbonate production rates tripled. Within four years, restored reefs were growing at the same speed as healthy reefs, and thereby provided the same important ecosystem functions.</p>
<p>This success is encouraging, but challenges still remain. The corals used to construct these restored reefs are predominantly branching coral types, chosen by the restoration team because they are easier to attach to the reef stars. This means that restored reefs have a lower diversity of coral types than healthy reefs, which host an abundance of boulder-like and encrusting corals as well as branching types. </p>
<p>These structural differences may affect the species of marine life that inhabit the reef. Branching corals are also notoriously sensitive to <a href="https://www.worldwildlife.org/pages/everything-you-need-to-know-about-coral-bleaching-and-how-we-can-stop-it">bleaching</a>, which happens when warmer water temperatures cause stress to corals and turn them white. Differences in the types of coral making up the reef ecosystem may therefore affect the reef’s ability to survive future heat waves. </p>
<h2>A warming world</h2>
<p>Marine heat waves are becoming <a href="https://theconversation.com/the-great-barrier-reef-has-been-bleaching-for-at-least-400-years-but-its-getting-worse-101691">more frequent and severe</a> and pose a huge threat to coral reefs and restoration efforts worldwide. Recently, thousands of <a href="https://theconversation.com/the-heroic-effort-to-save-floridas-coral-reef-from-extreme-ocean-heat-as-corals-bleach-across-the-caribbean-210974">nursery corals had to be rescued</a> when water temperatures spiked in the Florida Keys.</p>
<p>It’s imperative that coral reef restoration strategies include plans for warming waters. In some cases, efforts can be prioritised in areas where transplanted corals are less likely to encounter lethal conditions in the near future. In other cases, projects can enhance coral heat tolerance through <a href="https://theconversation.com/the-great-barrier-reef-can-repair-itself-with-a-little-help-from-science-85182">assisted evolution</a>. </p>
<p>There is some evidence that coral heat tolerance can also <a href="https://theconversation.com/remote-pacific-coral-reef-shows-at-least-some-ability-to-cope-with-ocean-warming-new-study-211852">increase naturally</a>. Whether this coral adaptation can keep pace with ocean warming will depend on global action to cut carbon emissions.</p>
<p>Outcomes of any reef restoration project will depend on environmental conditions, natural coral larvae supply, restoration techniques and the effort invested in maintaining the project. This Indonesian project shows that when conditions are right and efforts are well placed, success is possible. Hopefully, this inspires further global efforts to restore functioning coral reefs and to recreate a climate in which they can thrive.</p>
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<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>
<p><strong><em>Don’t have time to read about climate change as much as you’d like?</em></strong>
<br><em><a href="https://theconversation.com/uk/newsletters/imagine-57?utm_source=TCUK&utm_medium=linkback&utm_campaign=Imagine&utm_content=DontHaveTimeTop">Get a weekly roundup in your inbox instead.</a> Every Wednesday, The Conversation’s environment editor writes Imagine, a short email that goes a little deeper into just one climate issue. <a href="https://theconversation.com/uk/newsletters/imagine-57?utm_source=TCUK&utm_medium=linkback&utm_campaign=Imagine&utm_content=DontHaveTimeBottom">Join the 30,000+ readers who’ve subscribed so far.</a></em></p>
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<p class="fine-print"><em><span>Ines Lange receives funding from the Bertarelli Program in Marine Science. Logistical research support for this study was provided by Mars Sustainable Solutions.</span></em></p><p class="fine-print"><em><span>Tim Lamont receives funding from the Royal Commission for the Exhibition of 1851, and the Fisheries Society of the British Isles. </span></em></p><p class="fine-print"><em><span>Tries Blandine Razak 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>Artificial reef stars have been added to damaged coral reefs in Sulawesi, Indonesia. A new study shows that within just four years, restored reefs are thriving as much as healthy reefs.Ines Lange, Senior Research Fellow in Coral Reef Ecology, University of ExeterTim Lamont, Research Fellow, Lancaster UniversityTries Blandine Razak, Researcher, IPB UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2232072024-02-22T03:21:11Z2024-02-22T03:21:11ZSentinels of the sea: ancient boulder corals are key to reef survival in a warmer world<figure><img src="https://images.theconversation.com/files/574821/original/file-20240212-20-avdzaz.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5568%2C3700&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Giacomo d Orlando </span></span></figcaption></figure><p>Seas surrounding Australia this month hit an <a href="https://coralreefwatch.noaa.gov/data_current/5km/v3.1_op/daily/png/ct5km_baa5-max-7d_v3.1_seel_current.png">alarming level</a> of warming. It comes on the back of serious <a href="https://research.noaa.gov/2023/06/28/global-ocean-roiled-by-marine-heatwaves-with-more-on-the-way/">marine heatwaves</a> in the Northern Hemisphere summer.</p>
<p>Such warming is <a href="https://floridakeys.noaa.gov/corals/climatethreat.html#:%7E:text=Rising%20(or%20even%20falling)%20water,the%20coral%20turns%20completely%20white.">highly dangerous</a> for corals. Every <a href="https://www.annualreviews.org/doi/pdf/10.1146/annurev-animal-021122-093315">half a degree</a> of ocean warming increases their risk of bleaching and potential death.</p>
<p>The best long-term strategy to protecting Earth’s coral reefs is to dramatically cut greenhouse gas emissions and so limit global warming. But in the meantime, we must urgently make corals more resilient and protect those that are vulnerable.</p>
<p>That is particularly true for the huge, ancient features of reefs known as boulder corals. Research suggests they will be a vital part of reef survival in a warmer world.</p>
<figure class="align-center ">
<img alt="A map of Australia surrounded by patches of yellow, red and purple" src="https://images.theconversation.com/files/576928/original/file-20240221-26-asgzx0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/576928/original/file-20240221-26-asgzx0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=447&fit=crop&dpr=1 600w, https://images.theconversation.com/files/576928/original/file-20240221-26-asgzx0.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=447&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/576928/original/file-20240221-26-asgzx0.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=447&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/576928/original/file-20240221-26-asgzx0.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=562&fit=crop&dpr=1 754w, https://images.theconversation.com/files/576928/original/file-20240221-26-asgzx0.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=562&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/576928/original/file-20240221-26-asgzx0.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=562&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An image showing various levels of bleaching alert around Australia as of February 19, 2024.</span>
<span class="attribution"><span class="source">NOAA Coral Reef Watch</span></span>
</figcaption>
</figure>
<h2>The old-growth trees of the sea</h2>
<p>Boulder corals (<em>Porites</em>) can grow to more than <a href="https://link.springer.com/referenceworkentry/10.1007/978-90-481-2639-2_273#:%7E:text=Porites%20has%20attracted%20the%20attention,10%20m%20(indeterminate%20growth).">10m high</a> and live for <a href="https://onlinelibrary.wiley.com/doi/10.1111/brv.12391">more than 600 years</a>. In Australia they are often referred to as “bommies”. Each bommie can comprise multiple species, but they’re often a single massive individual.</p>
<p>The corals <a href="https://www.sciencedirect.com/science/article/pii/S0169534716000574?via%3Dihub">play a crucial role</a> in reefs, including providing habitat for marine life. Importantly, they can <a href="https://www.pnas.org/doi/full/10.1073/pnas.1716643115">maintain these functions</a> even when other coral species are absent.</p>
<p><a href="https://www.nature.com/articles/s41598-019-40150-3">Some species</a> are thought to be <a href="https://www.int-res.com/articles/meps2011/434/m434p067.pdf">resistant to stress</a>. Old corals have <a href="https://www.nature.com/articles/s41558-018-0351-2">likely experienced</a>
– and survived – past warming episodes, proving <a href="https://www.science.org/doi/10.1126/sciadv.abq8349">their resilience</a>.</p>
<p>For example, a paper in 2021 described a giant boulder coral discovered on the Great Barrier Reef which <a href="https://www.nature.com/articles/s41598-021-94818-w">was thought to be</a> more than 400 years old. It has survived 80 major cyclones, numerous coral bleaching events and centuries of exposure to other threats.</p>
<p>This resilience can benefit the whole reef ecosystem. We can think of boulder corals as akin to old-growth trees in a forest. Just like forests containing big, old trees are <a href="https://theconversation.com/contrary-to-common-belief-some-forests-get-more-fire-resistant-with-age-95059">more resistent</a> <a href="https://www.jstor.org/stable/26267895#:%7E:text=The%20adaptations%20of%20large%20trees,to%20withstand%20and%20survive%20fire.">to fire</a>, studies show a mix of different growth forms, including old and large boulder corals, <a href="https://www.nature.com/articles/s41558-021-01037-2">fare better</a> in the long-term under marine warming. </p>
<p>Older and bigger corals may also produce <a href="https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1002/ecy.1588?casa_token=tFnyWSTHmk0AAAAA:RkR06I_gTJk6p3vOCCdJdwku2CXO5tpUsChBn5_Nmhxfojl11fVg4uibQsWM4JFigd3dXzUYl_H8">more offspring</a>, so can more rapidly replenish the reef after disturbances.</p>
<p>Clearly, as our oceans face unprecedented pressures under climate change, we must protect – and learn from – these sentinels of the sea.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/snorkellers-discover-rare-giant-400-year-old-coral-one-of-the-oldest-on-the-great-barrier-reef-166278">Snorkellers discover rare, giant 400-year-old coral – one of the oldest on the Great Barrier Reef</a>
</strong>
</em>
</p>
<hr>
<h2>Preparing for the challenges ahead</h2>
<p>Understanding boulder corals is crucial to predicting how they might cope under climate change, and planning for their protection.</p>
<p>But scientists still have much to learn about boulder corals. In particular, we <a href="https://www.nature.com/articles/s41559-023-02319-y">don’t know</a> exactly how many species exist, their life histories and how they evolved. </p>
<p>My colleagues and I are aiming to overcome this knowledge gap. We are studying reefs across Australia, with a particular focus on boulder corals at Ningaloo Reef off Western Australia.</p>
<p>We are creating maps of what species of boulder corals exist and where they are located. And using cutting-edge <a href="https://threatenedspeciesinitiative.com/">genomics technology</a>, such as DNA sequencing, we are measuring the tolerance of each species to warming and trying to predict when they will reproduce. </p>
<p>Importantly, we are also examining the mutually beneficial relationship between the corals and algae. This relationship provides algae with shelter, gives corals their colour and provides nutrients to both partners. It may also be a <a href="https://link.springer.com/chapter/10.1007/978-3-319-75393-5_6">main factor</a> in coral resistance to warmer temperatures.</p>
<p>So far, we have found more diversity than initially expected. This is exciting because it may signal an increased capacity to resist different types of stress. But the work to fully map Ningaloo’s coral diversity has only just begun.</p>
<p>We hope our findings, once finalised, can inform local community management actions such as:</p>
<ul>
<li>public education campaigns and signs</li>
<li>managing visitor numbers to reefs</li>
<li>installing public moorings to reduce harm from boat anchoring, especially during coral spawning.</li>
</ul>
<p>The information can also be used in broader management actions such as:</p>
<ul>
<li>establishing “baseline” conditions from which to measure change</li>
<li>zoning decisions, including the establishment or ramping up of of marine park protections, especially for resilient coral species and individuals</li>
<li>impact assessments following events such as heatwaves</li>
<li>direct conservation actions for iconic, at-risk bommies, such as providing shade to diminish stress from heat</li>
<li>the development of national reef management plans.</li>
</ul>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/photos-from-the-field-why-losing-these-tiny-loyal-fish-to-climate-change-spells-disaster-for-coral-167119">Photos from the field: why losing these tiny, loyal fish to climate change spells disaster for coral</a>
</strong>
</em>
</p>
<hr>
<h2>Something worth fighting for</h2>
<p>The stress to coral wrought by recent marine heatwaves compounds damage incurred over decades. The Great Barrier Reef, for example, has <a href="https://theconversation.com/5-major-heatwaves-in-30-years-have-turned-the-great-barrier-reef-into-a-bleached-checkerboard-170719">experienced five</a> major heatwaves in 30 years. </p>
<p>Broadly, making reefs more resilient to these pressures involves:</p>
<ul>
<li>resisting, recovering, managing and adapting to shocks across ecosystems</li>
<li>improving governance structures</li>
<li>preparing human communities for change. </li>
</ul>
<p>Awareness of the need to increase reef resilience is growing. For example, it formed the basis of a 2017 <a href="https://elibrary.gbrmpa.gov.au/jspui/bitstream/11017/3287/1/GBRMPA%20Blueprint%20for%20Resilience%20-%20Low%20Res.pdf">blueprint</a> for the Great Barrier Reef and a <a href="https://www.barrierreef.org/uploads/Ningaloo-Strategy-v230216.pdf">strategy</a> for the Ningaloo Coast released last year.
But more work is required. </p>
<p>There’s also a need for coordination across Australia’s reef areas. This might include the exchange of knowledge and data between researchers and combined lobbying efforts to better protect reef ecosystems.</p>
<p>What’s more, Traditional Owners must be offered the opportunity to be consulted about, and meaningfully engaged in, protection of reef areas, including <a href="https://theconversation.com/climate-change-will-strike-australias-precious-world-heritage-sites-and-indigenous-knowledge-is-a-key-defence-222393?utm_medium=Social&utm_source=Twitter#Echobox=1707258796-1">co-management of Sea Country</a>.</p>
<p>The <a href="https://australiancoralreefsociety.org">Australian Coral Reef Society</a>, of which I am a councillor, last week released <a href="https://australiancoralreefsociety.org/acrs-letter-calling-parliament-reduce-atmospheric-carbon/">an open letter</a> to the federal government, calling for action on climate change to protect reefs. The task has never been more urgent. </p>
<p>There is still a lot of reef worth fighting for – but only if we act now.</p>
<p><em>The author would like to acknowledge the contribution of Ningaloo marine park managers – in particular, Dr Peter Barnes – to the research she and her colleagues are undertaking.</em></p><img src="https://counter.theconversation.com/content/223207/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kate Quigley receives funding from the Australian Research Council in the form of the Discovery Early Career Researcher Award (DECRA) and holds a joint position as Principal Research Scientist at Minderoo Foundation, a philanthropic organisation.</span></em></p>The best strategy to protecting Earth’s coral reefs is to dramatically cut greenhouse gas emissions. But in the meantime, we must urgently make corals more resilient.Kate Marie Quigley, DECRA Research Fellow (James Cook University), Principal Research Scientist (Minderoo Foundation), James Cook UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2239192024-02-21T19:01:08Z2024-02-21T19:01:08ZTracking tropical turtles deep down to the seabed reveals their feeding habits<p>Hawksbill turtles are <a href="https://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T8005A12881238.en">critically endangered</a>, they are found in every ocean and are the most tropical of sea turtles. Adult hawksbills have long been considered to have a close association with shallow (less than 15 metres depth) seas where coral reefs thrive.</p>
<p>But <a href="https://www.doi.org/10.1126/sciadv.adl2838">new research</a> my colleagues and I conducted reveals for the first time that hawksbill turtles feed at reef sites much deeper than previously thought. </p>
<p>Young hawksbills drift in currents during their pelagic (open water) phase of their development before they move to benthic (sea bed) habitats. Hawksbills are usually seen foraging in coral reefs where their diet is predominantly <a href="https://doi.org/10.3354/meps245249">sponges</a>. They also feed on a variety of algae, corallimorphs (coral-like anemones), tunicates and <a href="https://www.ajol.info/index.php/wiojms/article/view/66534">more</a>. </p>
<p>To study their feeding habits in more detail, my team at Swansea University used high-accuracy global positioning system (GPS) satellite tags to track 22 adult female hawksbills from their nesting site on Diego Garcia in the Chagos archipelago in the Indian Ocean to their foraging grounds. </p>
<p>Three of the tags included a pressure transducer that was programmed to record depth every five minutes and relay the measurement to the satellite system every time the turtle surfaced. This gave us information about the whereabouts of the turtles and how deep they were diving to feed as they swam.</p>
<p>We predicted that hawksbills tracked in our study would probably migrate to shallow coral reefs around the seven atolls of the Chagos archipelago. Many studies have shown the <a href="https://www.nature.com/articles/srep18289">pristine nature of these reefs</a> and we have previously observed hawksbills frequently foraging in reef habitats there. </p>
<p>But, surprisingly, all turtles migrated to deep, remote banks and submerged reefs in the archipelago, remaining at these deep sites for more than 6,000 combined days of tracking. By looking at nautical charts for the turtle locations, we could see that the foraging habitat was located at more than 30 metres depth. </p>
<p>More than 183,000 depth measurements relayed from the tags on three turtles showed that average depths were between 35 metres and 40 metres. <a href="https://doi.org/10.1126/sciadv.adl2838">Most dives reached depths between 30 metres and 60 metres</a>. That’s much deeper than we expected.</p>
<h2>Crucial for conservation</h2>
<p>The coral reefs located at depths of between 30 metres and 150 metres below the waves are known as mesophotic (or low light) ecosystems. Now, knowing that these habitats are so crucial for critically endangered sea turtles suggests that the marine life deep down on the seabed is much richer – with more nutritious food for turtles to eat – than previously thought. </p>
<p>We’d expect to find an abundance of colourful sponges and other invertebrate prey items such as soft corals that make up a big portion of the hawksbills’ diet. Our finding adds to the growing evidence that submerged banks at these mesophotic depths might be home to a diverse community of life, including <a href="https://www.ajol.info/index.php/wiojms/article/view/209266">sponges</a> and <a href="https://doi.org/10.1016/j.marpolbul.2018.03.018">seagrass</a> that are key foods for green turtles that also breed and forage in the western Indian Ocean. </p>
<p>Mesophotic ecosystems cover a vast area so they should be a significant part of conservation considerations. We estimated that submerged banks (at depths of 30 to 60 metres) in the western Indian Ocean extend across over 55,000 km² - around three times the size of a small country such as Wales.</p>
<p>Scientific understanding of mesophotic ecosystems is very poor, partly because they are difficult to explore. They are usually remote and far from land, plus the depths are often beyond the limit of routine scientific scuba diving. </p>
<p>There’s huge scope for more fascinating research to investigate the ecology of these misunderstood marine habitats. Recent studies have suggested <a href="https://doi.org/10.1371/journal.pone.0177374">rich biodiversity</a> and <a href="https://www.nature.com/articles/s41598-017-03568-1">abundant fish</a>, <a href="https://link.springer.com/article/10.1007/s00338-010-0593-6">corals and sponges</a> live at depths over 30 metres. </p>
<h2>Reef refuges</h2>
<p>With the pressures of climate change and warming seas, mesophotic reefs could be a refuge for corals and sponges that normally live in shallow coral reefs. For example, coral cover in Caribbean mesophotic reefs (30 to 40 metres depth) remained constant during hurricanes, bleaching and disease events in 2017 to 2019 when coral cover declined in shallow- and mid-water depths. That demonstrates the importance of these mesophotic reefs as a <a href="https://link.springer.com/article/10.1007/s00338-021-02087-w">reproductive refuge for corals</a>.</p>
<p>Our study findings highlight that submerged banks and mesophotic depths are important foraging grounds for critically endangered marine animals such as turtles and may support a rich array of marine life. While the mesophotic reefs used by foraging hawksbills in our study lie within one of the world’s largest marine protected areas, with <a href="https://doi.org/10.1007/s00227-020-03776-w">protection from industrial fishing</a>, there are ongoing negotiations for future conservation management of this region. </p>
<p>These submerged banks in the Chagos archipelago, and probably others around the world, should be key areas for conservation focus. The resilience of marine ecosystems, and all that lives within them, may rely on the health of these deeper, uncharted habitats, especially in the face of climate change.</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>
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</figure>
<p><strong><em>Don’t have time to read about climate change as much as you’d like?</em></strong>
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<p class="fine-print"><em><span>Nicole Esteban receives funding from the Bertarelli Foundation as part of the Bertarelli Programme in Marine Science (grant numbers BPMS-2017-4 and 820633).</span></em></p>Deeper ocean habitats (30-150 metres) are a key feeding ground for critically endangered hawksbill turtles.Nicole Esteban, Associate Professor of Marine Biology, Swansea UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2233222024-02-14T03:56:08Z2024-02-14T03:56:08ZThe world’s coral reefs are bigger than we thought – but it took satellites, snorkels and machine learning to see them<figure><img src="https://images.theconversation.com/files/575519/original/file-20240214-20-mjiqz2.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4607%2C2592&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/aerial-view-great-barrier-reef-whitsundays-1496224889">Shutterstock</a></span></figcaption></figure><p>The world’s coral reefs are close to 25% larger than we thought. By using satellite images, machine learning and on-ground knowledge from a global network of people living and working on coral reefs, <a href="https://www.sciencedirect.com/science/article/pii/S2949790624000016?via%3Dihub">we found</a> an extra 64,000 square kilometres of coral reefs – an area the size of Ireland. </p>
<p>That brings the total size of the planet’s shallow reefs (meaning 0-20 metres deep) to 348,000 square kilometres – the size of Germany. This figure represents whole coral reef ecosystems, ranging from sandy-bottomed lagoons with a little coral, to coral rubble flats, to living walls of coral. </p>
<p>Within this 348,000 km² of coral is 80,000 km² where there’s a hard bottom – rocks rather than sand. These areas are likely to be home to significant amounts of coral – the places snorkellers and scuba divers most like to visit. </p>
<p>You might wonder why we’re finding this out now. Didn’t we already know where the world’s reefs are? </p>
<p>Previously, we’ve had to pull data from many different sources, which made it harder to pin down the extent of coral reefs with certainty. But now we have high resolution satellite data covering the entire world – and are able to see reefs as deep as 30 metres down. </p>
<p>We coupled this with direct observations and records of coral reefs from over <a href="https://allencoralatlas.org/attribution">400 individuals and organisations</a> in countries with coral reefs from all regions, such as the Maldives, Cuba and Australia. </p>
<p>To produce the maps, we used machine learning techniques to chew through 100 trillion pixels from the Sentinel-2 and Planet Dove CubeSat satellites to make accurate predictions about where coral is – and is not. The team worked with almost 500 researchers and collaborators to make the maps. </p>
<p>The result: the world’s first comprehensive map of coral reefs extent, and their composition, produced through the <a href="https://allencoralatlas.org/">Allen Coral Atlas</a>. </p>
<p>The maps are already proving their worth. Reef management agencies around the world are using them to plan and assess conservation work and threats to reefs. </p>
<figure class="align-center ">
<img alt="Researcher towing a GPS on Great Barrier Reef during an expedition." src="https://images.theconversation.com/files/575477/original/file-20240213-26-wxc8ic.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/575477/original/file-20240213-26-wxc8ic.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/575477/original/file-20240213-26-wxc8ic.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/575477/original/file-20240213-26-wxc8ic.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/575477/original/file-20240213-26-wxc8ic.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/575477/original/file-20240213-26-wxc8ic.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/575477/original/file-20240213-26-wxc8ic.png?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">We combined satellite data with real world observations. Here, Dr Eva Kovacs tows a GPS on the Great Barrier Reef.</span>
<span class="attribution"><a class="source" href="https://allencoralatlas.org/blog/meet-the-team-university-of-queensland/">Allan Coral Atlas</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Where is this hidden coral?</h2>
<p>You can see the difference for yourself. In the interactive slider below, red indicates the newly detected coral in reefs off far north Queensland. </p>
<p><iframe id="tc-infographic-1015" class="tc-infographic" height="400px" src="https://cdn.theconversation.com/infographics/1015/df887cb0211a347030b52f7e8261bcacbc7e9463/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>This infographic shows the new detail we now have for the Tongue Reef, in the seas off Port Douglas in Far North Queensland. </p>
<p><iframe id="tc-infographic-1017" class="tc-infographic" height="400px" src="https://cdn.theconversation.com/infographics/1017/21ab9e743c8e2a3a716df327b0946c4bf8e47468/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Our maps have three levels of detail. The first is the most expansive – the entire coral reef ecosystem. Seen from space, it has light areas of coral fringed by darker deeper water. </p>
<p>Then we have geomorphic detail, meaning what the areas within the reef look like. This includes sandy lagoons, reef crests exposed to the air at low tide, sloping areas going into deeper water and so on.</p>
<p><iframe id="tc-infographic-1016" class="tc-infographic" height="400px" src="https://cdn.theconversation.com/infographics/1016/ba3212ee64a358a16ca6b5ccfb454b415a72afe1/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>And finally we have fine detail of the benthic substrates, showing where you have areas dominated by coral cover. </p>
<p>Coral can’t grow on sand. Polyps have to attach to a hard surface such as rock before they can begin expanding the reef out of their limestone-secreting bodies. </p>
<p>Some of our maps include fine detail of benthic substrates, meaning where coral is most likely to be and the substrates (seafloor) available to the polyps, such as existing coral, sand, rubble, or seagrass. </p>
<iframe src="https://flo.uri.sh/visualisation/16796582/embed" title="Interactive or visual content" class="flourish-embed-iframe" frameborder="0" scrolling="no" style="width:100%;height:600px;" sandbox="allow-same-origin allow-forms allow-scripts allow-downloads allow-popups allow-popups-to-escape-sandbox allow-top-navigation-by-user-activation" width="100%" height="400"></iframe>
<div style="width:100%!;margin-top:4px!important;text-align:right!important;"><a class="flourish-credit" href="https://public.flourish.studio/visualisation/16796582/?utm_source=embed&utm_campaign=visualisation/16796582" target="_top"><img alt="Made with Flourish" src="https://public.flourish.studio/resources/made_with_flourish.svg"></a></div>
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<div style="width:100%!;margin-top:4px!important;text-align:right!important;"><a class="flourish-credit" href="https://public.flourish.studio/visualisation/16784641/?utm_source=embed&utm_campaign=visualisation/16784641" target="_top"><img alt="Made with Flourish" src="https://public.flourish.studio/resources/made_with_flourish.svg"></a></div>
<p>It’s a crucial time for the world’s coral reefs. We’re discovering the full extent of shallow water reefs – while other researchers are finding large new <a href="https://www.theguardian.com/environment/2024/jan/19/deep-sea-coral-reef-atlantic-coast">black coral reefs</a> in deeper water. </p>
<p>But even as we make these discoveries, coral reefs are reeling. Climate change is steadily heating up the sea and making it more acidic. Coral polyps can’t <a href="https://theconversation.com/the-heroic-effort-to-save-floridas-coral-reef-from-extreme-ocean-heat-as-corals-bleach-across-the-caribbean-210974">handle too much heat</a>. These wonders of biodiversity are home to a quarter of the ocean’s species.</p>
<figure class="align-center ">
<img alt="Scientist doing coral reef research." src="https://images.theconversation.com/files/575481/original/file-20240213-20-h7bnsp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/575481/original/file-20240213-20-h7bnsp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/575481/original/file-20240213-20-h7bnsp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/575481/original/file-20240213-20-h7bnsp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/575481/original/file-20240213-20-h7bnsp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=423&fit=crop&dpr=1 754w, https://images.theconversation.com/files/575481/original/file-20240213-20-h7bnsp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=423&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/575481/original/file-20240213-20-h7bnsp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=423&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Making these maps took plenty of underwater research as well as satellite data. This photo shows Dr Chris Roelfsema conducting a photo transect in a remote area of the Great Barrier Reef.</span>
<span class="attribution"><a class="source" href="https://allencoralatlas.org/blog/new-funds-for-coral-reef-field-engagement/">Allen Coral Atlas</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>In good news, these maps are already leading to real world change. We’ve already seen new efforts to conserve coral reefs in Indonesia, several Pacific island nations, Panama, Belize, Kenya and Australia, among others. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-do-coral-reefs-thrive-in-parts-of-the-ocean-that-are-low-in-nutrients-by-eating-their-algal-companions-212049">How do coral reefs thrive in parts of the ocean that are low in nutrients? By eating their algal companions</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/223322/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mitchell Lyons receives funding from Australian Research Council and Australian Commonwealth Government. Mitchell Lyons works for the University of Queensland and the University of New South Wales. </span></em></p><p class="fine-print"><em><span>Stuart Phinn receives funding from the Australian Research Council, Queensland and New South Wales state governments, Geoscience Australia and other Commonwealth agencies, and SmartSAT CRC. He works for the University of Queensland and was the founding director of Earth Observation Australia and Australia's Terrestrial Ecosystem Research Network (TERN). </span></em></p>Our new maps show coral reefs are more extensive than we thought.Mitchell Lyons, Postdoctoral research fellow, The University of QueenslandStuart Phinn, Professor of Geography, Director - Remote Sensing Research Centre, Chair - Earth Observation Australia, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2211112024-01-24T18:43:10Z2024-01-24T18:43:10ZUsing photos to create 3D models is helping us understand – and protect – complex marine environments<figure><img src="https://images.theconversation.com/files/570263/original/file-20240118-16-o98su0.jpg?ixlib=rb-1.1.0&rect=52%2C19%2C3137%2C2118&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Matteo Collina</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Measuring the impact of different events, such as marine heatwaves, on the abundance of marine organisms is not easy. Biological communities naturally change over time and between different locations. </p>
<p>Scientists need to untangle these natural changes from those caused by humans and come up with a new approach to do this.</p>
<p>Marine biologists have traditionally monitored underwater cliffs or coral reefs by estimating population sizes in just a small area of those environments. </p>
<p>One traditional method involves laying a tape measure on the reef and determining what was under the tape at regular intervals. Another is to take pictures of “quadrats” – squares of a known area – and working out the area covered by different organisms later. </p>
<p>However, these methods only provide an estimate for a very small area of the total reef, covering a limited proportion of the animals and plants present. </p>
<p>They also provide limited information on the three-dimensional (3D) reef complexity and structure created by reef organisms, such as corals and sponges, which are key to supporting high <a href="https://www.worldwildlife.org/pages/what-is-biodiversity#:%7E:text=Biodiversity%20is%20all%20the%20different,maintain%20balance%20and%20support%20life.">biodiversity</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/loss-decay-and-bleaching-why-sponges-may-be-the-canary-in-the-coal-mine-for-impacts-of-marine-heatwaves-194146">Loss, decay and bleaching: why sponges may be the ‘canary in the coal mine’ for impacts of marine heatwaves</a>
</strong>
</em>
</p>
<hr>
<p>Our <a href="https://www.sciencedirect.com/science/article/pii/S0141113623003823">new research</a> shows how modern photographic methods can be used to measure coral reef habitat complexity, and the 3D nature of reefs. </p>
<p>This information was then used to assess the impacts of changes from <a href="https://theconversation.com/the-rise-of-sponges-in-anthropocene-reef-ecosystems-105493">coral-dominated reefs to sponge-dominated reefs</a> on the spaces available for fish and other organisms to live. </p>
<p>Here’s how it works.</p>
<h2>An art and a science</h2>
<p>Photogrammetry – a technique where 3D information is extracted from photographs – is both an art and science. The process involves taking a large number of images of an object or area from different angles. Using specialised algorithms we can then analyse and convert these pictures into 3D digital models. </p>
<p>These models can be appropriately scaled to real-world dimensions, allowing accurate measurements of organisms. </p>
<p>While photogrammetry is not new, its application to marine science has <a href="https://link.springer.com/article/10.1007/s00338-023-02445-w">increased in recent years</a>. It is completely changing the way we can monitor marine environments and measure human impacts. </p>
<p>However, there are many other ways broader photogrammetric tools can be used, from <a href="https://theconversation.com/how-do-you-weigh-a-live-whale-124363">estimating the size of whales</a> to developing realistic simulations or virtual reality experiences for education.</p>
<p>Our <a href="https://www.sciencedirect.com/science/article/pii/S0141113623003823">recently published study from Indonesia</a> used photogrammetry to estimate the potential impacts of changes from coral-dominated to sponge-dominated tropical reefs on reef structural complexity. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-irish-lough-that-offers-a-window-into-the-deep-sea-161438">The Irish lough that offers a window into the deep sea</a>
</strong>
</em>
</p>
<hr>
<p>The study compared the structural complexity of coral and sponge-dominated areas of a coral reef. By using photogrammetry, we were able to better understand the different factors that contributed to the coral’s structural complexity in a way that would not be possible from traditional 2D photographs. </p>
<p>This study found sponge-dominated reefs had fewer of the smallest spaces for fish and other organisms to live, whereas coral-dominated reefs had fewer larger spaces. </p>
<p>This information is important. The smallest spaces on coral reefs are occupied by small fish and other species that feed animals higher up the food chain. As coral reefs lose these small refuge spaces, they also lose the ability to support biodiversity.</p>
<h2>Going bigger</h2>
<p>While the Indonesian study examined only small sections of the reef, the use of photogrammetry for monitoring and mapping marine ecosystems is expanding rapidly. </p>
<p>Thanks to modern hardware and software solutions, it is now possible to rapidly create models for much larger areas. And thanks to high-resolution photography, even the smallest animals can be identified in the models. </p>
<p>These models are complementing the use of traditional sampling methods that only estimate the abundances of organisms in a small area of a reef. But we also have the potential to now sample entire reefs.</p>
<p>As models of reefs derived from photogrammetry are 3D, there are many different new sources of information that can be collected, such as accurate surface areas and volumes of organisms. </p>
<p>For many organisms, like sponges and corals, surface areas and volumes are more important in measuring their ecological importance than just the amount of reef they cover.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/xDaMNbqs4WY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An example of the Fiordland underwater environment rendered through a game engine, and ready to be used for VR applications.</span></figcaption>
</figure>
<p>Moreover, 3D models of large areas can be oriented and scaled or geo-referenced, essentially creating all the characteristics of a typical map. This makes finding previously surveyed areas much easier. </p>
<p>The overall result is better characterisation of marine communities. This makes it easier to monitor and visualise changes, and the effects of different factors, such as marine heatwaves.</p>
<p>Finally, scaled 3D representations can be created for complex organisms, meaning growth and shape changes can be more accurately measured. This provides a greater understanding of how environmental change affects organisms. </p>
<h2>Visualising changes in biodiversity</h2>
<p>Virtual reality has long been used to provide access to marine environments without getting wet. This has been done largely for education, outreach and training opportunities. </p>
<p>But 3D models created from photogrammetry provide new and exciting opportunities to engage the public. People can now interact with the environment, experiencing new worlds and points of view, while learning and increasing their environmental consciousness.</p>
<p>The application of 3D models derived from underwater photogrammetry has great potential for the monitoring of marine environments and detecting the impact of humans. </p>
<p>These models represent a transformative shift in the way information is gathered in marine ecosystems. As technology develops further they will support more extensive marine monitoring and more effective management.</p>
<figure>
<div class="sketchfab-embed-wrapper">
<iframe title="Breaker Bay Reef" frameborder="0" allowfullscreen="" mozallowfullscreen="true" webkitallowfullscreen="true" allow="autoplay; fullscreen; xr-spatial-tracking" xr-spatial-tracking="" execution-while-out-of-viewport="" execution-while-not-rendered="" web-share="" src="https://sketchfab.com/models/2fb4762881b54f3296e6d39a841dd44b/embed" <="" iframe="" width="100%" height="400">
</div>
<figcaption><span class="caption">An example of a 3D model of Breaker Bay Reef in Wellington, New Zealand.</span></figcaption>
</figure></iframe></div></figure><img src="https://counter.theconversation.com/content/221111/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Bell receives funding from Operation Wallacea and Victoria University of Wellington, and has previously received funding form the Royal Society of New Zealand (Marsden Fund).</span></em></p><p class="fine-print"><em><span>Alberto Rovellini has previously received support from the Royal Society of New Zealand (Marsden Fund), Victoria University of Wellington, and Operation Wallacea </span></em></p><p class="fine-print"><em><span>Matteo Collina and Miriam Pierotti 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>Photogrammetry, a technique where 3D information is extracted from photographs, is reducing the guesswork in counting – and understanding – the world below the ocean surface.Professor James J Bell, Professor of Marine Biology, Te Herenga Waka — Victoria University of WellingtonAlberto Rovellini, Postdoctoral fellow, University of WashingtonMatteo Collina, PhD candidate, Te Herenga Waka — Victoria University of WellingtonMiriam Pierotti, PhD candidate, Te Herenga Waka — Victoria University of WellingtonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2207602024-01-18T13:28:52Z2024-01-18T13:28:52ZNot all underwater reefs are made of coral − the US has created artificial reefs from sunken ships, radio towers, boxcars and even voting machines<figure><img src="https://images.theconversation.com/files/569704/original/file-20240116-27-b90elk.jpg?ixlib=rb-1.1.0&rect=8%2C0%2C5682%2C3788&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The bow of the U.S. Coast Guard cutter Duane, a decommissioned ship deliberately sunk off Florida to serve as an artificial reef.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/bow-of-uscg-duane-royalty-free-image/492717259">Stephen Frink via Getty Images</a></span></figcaption></figure><p>When people hear about underwater reefs, they usually picture colorful gardens created from coral. But some reefs are anchored to much more unusual foundations. </p>
<p>For more than a century, people have placed a wide assortment of objects on the seafloor off the U.S. coast to provide habitat for marine life and recreational opportunities for fishing and diving. Artificial reefs have been created from decommissioned ships, chicken transport cages, concrete pipes, rail cars and more.</p>
<p>We study how ocean-dwelling fish <a href="https://scholar.google.com/citations?user=wZ-kv2AAAAAJ&hl=en">use artificial reefs</a> in the <a href="https://scholar.google.com/citations?user=WF8vzA4AAAAJ">U.S. and beyond</a>. Through our research, we have learned that artificial reefs can be hot spots for large predatory fish such as <a href="https://doi.org/10.1111/faf.12548">groupers</a> and <a href="https://doi.org/10.1371/journal.pone.0237374">jacks</a>. They also can serve as <a href="https://doi.org/10.1038/s42003-019-0398-2">stepping stones</a> for reef fish expanding their range northward with warming water temperatures and as <a href="https://doi.org/10.1002/ecy.2687">rest stops</a> for sharks. </p>
<p>Artificial reefs can be <a href="https://doi.org/10.1002/ecs2.3924">strategically designed and placed</a> to optimize fish habitat. But although they provide valuable ecological services, no one has inventoried how many of these structures exist in U.S. waters or how much seafloor they occupy.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/569699/original/file-20240116-25-xly63u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Fish swim through a sunken ship doorway rimmed with coral as a scuba diver hovers nearby." src="https://images.theconversation.com/files/569699/original/file-20240116-25-xly63u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/569699/original/file-20240116-25-xly63u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/569699/original/file-20240116-25-xly63u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/569699/original/file-20240116-25-xly63u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/569699/original/file-20240116-25-xly63u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/569699/original/file-20240116-25-xly63u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/569699/original/file-20240116-25-xly63u.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"></a>
<figcaption>
<span class="caption">A diver at the U.S. Coast Guard cutter Duane, which was decommissioned in 1985 and intentionally sunk in 1987 off Key Largo, Fla., to create reef habitat.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/diver-on-shipwreck-royalty-free-image/109010339">Stephen Frink/The Image Bank via Getty Images</a></span>
</figcaption>
</figure>
<p>To help fill this knowledge gap, we led a team of scientists and artificial reef directors from the 17 U.S. states with artificial reef-building programs in the first national calculation of artificial reef extent. Our <a href="https://www.nature.com/articles/s41893-023-01258-7">new study</a> shows that these reefs cover a total of about 7 square miles (19 square kilometers) of U.S. seafloor – an area equivalent to 3,600 football fields. We also describe the diversity of objects used to create reefs, as well as patterns in artificial reef creation over time.</p>
<h2>Creating modern artificial reefs</h2>
<p>Modern reefing is different from dumping trash into the water and is <a href="https://media.fisheries.noaa.gov/dam-migration/noaa_artificial_reef_guidelines.pdf">regulated at the federal and state levels</a>. A rigorous permitting and approval process ensures that the proposed objects or materials are appropriate to deploy in the ocean. </p>
<p>For example, decommissioned ships are thoroughly <a href="https://www.epa.gov/ocean-dumping/vessel-reef-projects">cleaned and drained of fuel and other polluting substances</a> prior to sinking to minimize environmental risks. Some materials that were once used to create artificial reefs, such as rubber, fiberglass, wood and plastic, are now prohibited because they may move from their placed location, damaging nearby habitat, or deteriorate quickly in salt water. </p>
<p>Reefed objects can be sunk only in predesignated areas of the U.S. seafloor. These zones, which are usually sandy sea bottom, total about 2,200 square miles (5,800 square kilometers) – roughly the area of Delaware.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/48Py7uILHHg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Seven months after the Texas Parks and Wildlife Dept.’s artificial reef program sank the Kraken, a decommissioned 371-foot cargo ship, divers found it heavily colonized by ocean life.</span></figcaption>
</figure>
<p>Each zone can support the creation of many individual reefs over multiple decades. Within a given zone, reefed objects are usually placed away from one another, separated by large swaths of sand. This maximizes the amount of sand habitat, where some reef fish forage.</p>
<p>The extent of artificial reefs in these zones has increased by about 2,000% over the past 50 years. Since 2010, however, artificial reef extent has grown only 12%. This is likely because of challenges in acquiring and sinking acceptable reef materials. It could also reflect a push toward <a href="https://theconversation.com/3d-printing-coral-reefs-can-create-new-habitat-but-it-doesnt-tackle-human-destruction-103927">developing structures</a> specifically for use as artificial reefs. </p>
<h2>Planes, trains and automobiles</h2>
<p>For our study, we gathered records of intentional reefings dating back to 1899 and occurring off artificial all U.S. coastal states, except for six without artificial ocean reef programs: Maine, New Hampshire, Connecticut, Oregon, Washington and Alaska.</p>
<p>For some of these events, especially in recent decades, there were detailed records of the sizes and quantities of sunken objects or seafloor maps from which we could derive these measurements. These reefs were easy to quantify. </p>
<p>Other records, including some from the early 20th century, had scant detail. For these, we developed an approach to estimate how much seafloor the reefs covered, based on similar deployments with better records.</p>
<p>Our study found a vast assortment of reefed objects on the U.S. seafloor. They included decommissioned tugboats, fishing vessels, barges, ferries and military vessels. Reefs have also been created from rail boxcars, aircraft, vehicles, chicken transport cages, voting machines, missile platforms, concrete pipes, radio towers, tires, limestone rocks and objects purposely designed as artificial reefs.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/569701/original/file-20240116-19-2hqu7p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A boat with a crane lowers pyramid-shaped structures into the water." src="https://images.theconversation.com/files/569701/original/file-20240116-19-2hqu7p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/569701/original/file-20240116-19-2hqu7p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/569701/original/file-20240116-19-2hqu7p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/569701/original/file-20240116-19-2hqu7p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/569701/original/file-20240116-19-2hqu7p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/569701/original/file-20240116-19-2hqu7p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/569701/original/file-20240116-19-2hqu7p.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">The Florida Fish and Wildlife Commission deploys artificial reef modules off the coast of Mexico Beach on April 6, 2013.</span>
<span class="attribution"><a class="source" href="https://flic.kr/p/eh6fXS">Florida Fish and Wildlife Commission/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Objects that occupy the largest amount of seafloor include limestone rocks, large concrete modules designed specifically for reefing, metal rigs and towers and long, narrow concrete pieces repurposed from their previous uses, such as culverts or bridges.</p>
<h2>Potential impacts</h2>
<p>After a reef is created, fish can appear within minutes or hours. The sequence of fish arrival sometimes <a href="https://doi.org/10.1016/j.ecoleng.2018.09.012">follows a pattern</a>. Transient fish such as jacks and barracuda come first, followed by bottom-dwelling fish such as grouper and smaller reef fish. With time, plants and animals grow on the hard surfaces of the artificial reef, helping to provide food and sanctuary for fish.</p>
<p>However, these reefs can also cause ecological harm. Invasive species, such as plants and other animals that grow on hard structures, can use artificial reefs to <a href="https://doi.org/10.1371/journal.pone.0038124">spread to new places</a>. </p>
<p>Artificial reefs also may attract fish away from nearby natural reefs. Since constructed reefs are often in prime recreational fishing locations, this could lead to higher catches of those species. </p>
<p>Another risk is that if artificial reefs are improperly placed or secured on the sea floor, they can shift into unintended areas and harm sensitive habitats, particularly in the aftermath of storms. For example, Florida <a href="https://www.theguardian.com/us-news/2015/may/22/florida-retrieving-700000-tires-after-failed-bid-to-create-artifical-reef">sank 1 million to 2 million tires offshore</a> in the 1970s in an effort to create artificial reefs, but sea life didn’t colonize them as intended. Now the tires are washing around and smothering coral.</p>
<p><div data-react-class="InstagramEmbed" data-react-props="{"url":"https://www.instagram.com/reel/CxvnpSdOnsr/?utm_source=ig_web_copy_link","accessToken":"127105130696839|b4b75090c9688d81dfd245afe6052f20"}"></div></p>
<h2>Learning from artificial reefs</h2>
<p>Monitoring how fish and other species use artificial reefs, especially compared with naturally occurring reefs, will be key for understanding benefits and risks from these structures. As <a href="https://theconversation.com/artificial-coral-reefs-showing-early-signs-they-can-mimic-real-reefs-killed-by-climate-change-new-research-215011">climate change</a> continues to alter ocean ecosystems, we see opportunities to learn which types of artificial reefs are best suited for enhancing habitat for particular sorts of fish. </p>
<p>For example, we know that large predators that dwell in open water, such as jacks, barracuda and sharks, tend to prefer <a href="https://doi.org/10.1371/journal.pone.0237374">taller artificial reefs over shorter ones</a>. This is similar to insights from oil rigs, showing that these vertical and complex structures are <a href="https://doi.org/10.1073/pnas.1411477111">valuable fish habitat</a>. More than 500 decommissioned oil rigs <a href="https://www.bsee.gov/what-we-do/environmental-compliance/environmental-programs/rigs-to-reefs">have been converted to reefs</a>. Our calculation included only those that are managed by state artificial reef programs. </p>
<p>Other structures in the water, such as <a href="https://theconversation.com/as-the-us-begins-to-build-offshore-wind-farms-scientists-say-many-questions-remain-about-impacts-on-the-oceans-and-marine-life-216330">offshore wind turbine foundations</a>, will <a href="https://youtu.be/0SBxDWuE1vY">likely form habitat for sea life</a> similarly to artificial reefs. Insights about what types of structures different fish prefer may help guide the design or location of offshore wind farms.</p>
<p>Humans rely on the ocean for many benefits, including food, commerce, energy and a stable climate. Measuring artificial reefs’ footprint is a first step toward understanding their effects, both good and bad, on ocean wildlife and human uses of the ocean.</p>
<p><em><a href="https://www.nature.org/en-us/about-us/where-we-work/united-states/virginia/stories-in-virginia/our-staff/">Brendan Runde</a>, a marine scientist at The Nature Conservancy, contributed to this article.</em></p><img src="https://counter.theconversation.com/content/220760/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Artificial reefs are structures that humans put in place underwater that create habitat for sea life. A new study shows for the first time how much of the US ocean floor they cover.Avery Paxton, Research Marine Biologist, National Oceanic and Atmospheric AdministrationD'amy Steward, Master's Student in Biology, University of GuamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2091962024-01-08T13:36:16Z2024-01-08T13:36:16ZWhat happens to the ocean if we take out all the fish? A marine ecologist explains the complex roles fish play in their ecosystem<figure><img src="https://images.theconversation.com/files/543088/original/file-20230816-19-h6b36a.jpg?ixlib=rb-1.1.0&rect=6%2C12%2C2038%2C1348&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Fish swim in a reef at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands.</span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/UNBiodiversity/3ead5d56c624402893c0df11ab789657/photo?Query=ocean%20fish&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=262&currentItemNo=31&vs=true">AP Photo/Jacob Asher </a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&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>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>What would happen to the ocean if we took out all the fish? – Reny, age 12</strong></p>
</blockquote>
<hr>
<p>The ocean is massive and covers most of the surface of our planet. In addition to its size, it’s packed with life, ranging from an astounding diversity of plants, microbes, worms, corals and crabs to squids, whales and, yes, even fish. The ocean is full of fish, so much so that they make up the <a href="https://doi.org/10.1073/pnas.1711842115">second-largest amount of all carbon</a> – the material that makes up living things – in the entire animal kingdom. They’re just behind the group containing insects and crustaceans.</p>
<p>Most people only interact with the ocean from a beach or in a boat, so it can be hard to wrap your head around how many fish there really are. But the ocean is swarming with them, from its surface <a href="https://www.nbcnews.com/news/world/deepest-ever-fish-filmed-japan-scientists-rcna77858">to its depths</a>. </p>
<p>These fish also come in all kinds of shapes and sizes, ranging from the tiny sardines, guppies and blennies that you might <a href="https://www.palmbeachpost.com/story/opinion/columns/guest/2020/01/25/point-of-view-call-for-more-diversity-not-only-more-fish-in-marine-protected-areas/112150854/">see on a coral reef</a> to massive tunas and whale sharks that you might find <a href="https://www.fisheries.noaa.gov/feature-story/surface-slicks-are-pelagic-nurseries-diverse-ocean-fauna">out in the open ocean</a>. </p>
<p>These fish perform all kinds of <a href="https://doi.org/10.1002/ecs2.4288">roles in their ecosystems</a> that support the lives of other organisms around them. If they disappeared one day, the ocean would look very different.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/542471/original/file-20230813-127481-q0e3vz.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">School of slopehead parrotfish.</span>
<span class="attribution"><span class="source">NOAA, Kevin Lino</span></span>
</figcaption>
</figure>
<p>I’m a <a href="https://koryevans.weebly.com/">scientist who studies fish</a>, their diversity and all the ways they contribute to ocean environments.</p>
<h2>Fish as food</h2>
<p>Fish play important roles as both <a href="https://www.noaa.gov/education/resource-collections/marine-life/aquatic-food-webs">predators and prey</a> in ocean ecosystems. Thousands of species throughout the ocean and terrestrial ecosystems rely on fish for food – <a href="https://www.fisheries.noaa.gov/feature-story/economic-importance-seafood">including people</a>. </p>
<p>In coral reef ecosystems, small fish are eaten by larger fish and other marine animals. This means the little fish form the base of the food web – they provide energy to the bigger fish and other creatures. </p>
<figure class="align-center ">
<img alt="Conceptual food web of a coral reef ecosystem identifying key functional groups." src="https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=569&fit=crop&dpr=1 600w, https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=569&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=569&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=715&fit=crop&dpr=1 754w, https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=715&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/542472/original/file-20230813-197557-ebgabl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=715&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Links between different species of coral reef animals.</span>
<span class="attribution"><span class="source">Global Change Biology, Rogers et al., 2015</span></span>
</figcaption>
</figure>
<p>Outside of the water, many birds, mammals and reptiles eat fish and rely on them as an <a href="https://doi.org/10.1016/S0921-8009(99)00015-4">essential source of protein</a>. </p>
<p>Even land plants can benefit from the presence of fish. On the western coast of the United States, salmon returning to small streams after spending several years at sea function as a conveyor belt of nutrients. The salmon feed not only animals that catch them, like bears, but also the plants that border the streams. Studies have shown that some plants get <a href="https://www.adfg.alaska.gov/index.cfm?adfg=wildlifenews.view_article&articles_id=407">70% of their nitrogen</a> from salmon that die on or near the river banks. </p>
<p>Humans also depend on fish as a food source. Fish and other seafood products are an important protein source for <a href="https://www.nature.org/en-us/what-we-do/our-priorities/provide-food-and-water-sustainably/food-and-water-stories/global-fisheries/">nearly 3 billion people</a>. Human populations have been eating and following fish around the world for <a href="https://doi.org/10.1073/pnas.1710186114">thousands of years</a>. </p>
<h2>Fish maintain habitats</h2>
<p>Fish are also more than just food. As fish themselves forage for food, they can create and maintain important <a href="https://doi.org/10.1007/s00338-006-0112-y">habitats for other organisms</a>. In coral reef ecosystems, plant-eating fish control the growth of algae by constantly grazing it down. Without the help of these herbivores, or plant-eating fish, the algae would rapidly grow and smother the coral, effectively killing it. </p>
<p>One type of herbivorous fish, the parrotfish, <a href="https://ocean.si.edu/ocean-life/fish/tough-teeth-and-parrotfish-poop">feeds directly on the corals</a>. At first, this may seem bad for the corals, but the grazing done by parrotfish can actually increase a coral colony’s rate of growth. And <a href="https://ocean.si.edu/ocean-life/fish/tough-teeth-and-parrotfish-poop">the poop</a> – yes, the poop – from parrotfish has been shown to be <a href="https://doi.org/10.1016/j.tim.2022.03.006">particularly nutritious</a> for corals. Parrotfish poop also forms part of the <a href="https://ocean.si.edu/ocean-life/fish/tough-teeth-and-parrotfish-poop">beautiful white sand beaches</a> that you may have enjoyed on a family vacation.</p>
<p>Other fish create habitats for other animals and influence their environment by <a href="https://www.ingentaconnect.com/content/umrsmas/bullmar/1986/00000038/00000001/art00006">disturbing sand</a> while they feed. By moving the sand around, they’re exposing tiny organisms hiding in the sand, which other animals can eat. </p>
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<figcaption><span class="caption">Some fish sift through sand to find their food. That creates more opportunities for other creatures to find food in the sand.</span></figcaption>
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<p>Despite the fact that many types of fish are confined to the ocean, their presence can be felt across many habitats. They can directly and indirectly affect the lives of the organisms that depend on them for food and shelter. Without fish, Earth would gradually lose its beautiful white sand beaches, the coral reef ecosystems would be overgrown with algae, lots of people would run out of food to eat, and we would lose some of the planet’s most fascinating creatures.</p>
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<p class="fine-print"><em><span>Kory Evans receives funding from National Science Foundation. </span></em></p>There are so many fish in the ocean that if you took them out, important habitats and food sources for many creatures would be lost.Kory Evans, Assistant Professor of BioSciences, Rice UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1943352023-12-10T19:07:20Z2023-12-10T19:07:20ZHow an underwater sculpture trail plays a role in the health – and beauty – of the Great Barrier Reef<p>The widespread demise of coral reefs due to climate change is <a href="https://www.ipcc.ch/report/ar6/syr/downloads/report/IPCC_AR6_SYR_SPM.pdf">now a certainty</a>. But what role does art have in our future for coral reefs? </p>
<p>Art is about feelings. One of the great challenges today is that we often feel untouched by the problems of others and by global issues like climate change. This is where art can make a difference.</p>
<p>Engaging with a thoughtful work of art can connect you to your senses, body and mind. Art can be used as a tool to raise awareness, promote conversation and rally behind a cause. </p>
<p>One way this is happening on the Great Barrier Reef is through an underwater sculpture trail. Here reef sculptures are drawing attention to inspirational scientists, the science of climate change, reef restoration, citizen science and traditional culture.</p>
<h2>What are reef sculptures?</h2>
<p>Reef sculptures are a form of artificial reef: man-made structures placed into an aquatic environment to mimic certain characteristics of a natural reef.</p>
<p>Artificial reefs were historically deployed for fishers and divers to concentrate marine life and to shift pressure from other popular locations.</p>
<p>Artificial reefs take many forms, such as reef balls, pods, concrete pipes, wrecks and sculptures. They can be sites of ecological research, conservation and arts and culture.</p>
<p>The first modern reef sculpture was created by Jason deCaires Taylor at Grenada in the West Indies in 2006. This sculpture aimed to provide a restorative response to a damaged marine ecosystem and enhance marine tourism. </p>
<p>The largest underwater sculpture in the world is the <a href="https://www.moua.com.au/">Museum of Underwater Art</a> created with deCaires Taylor at John Brewer Reef, offshore from Townsville. The Coral Greenhouse is a skeletal building made from pH-neutral cement and corrosion-resistant stainless steel. It covers an area of 72 square metres and weights 165 tonnes, with eight human figures depicting scientists, conservationists and coral gardeners.</p>
<p>A <a href="https://www.mdpi.com/2077-1312/10/11/1617">recent report</a> on this sculpture found statistically significant increases in fish abundance and diversity. There were no changes over time in invertebrate abundance, invertebrate diversity and tourist perceptions of aesthetic values.</p>
<p>Structural designs of underwater sculptures need to be able to adapt into the surrounding natural landscape, creating a transition point from the manufactured to natural. </p>
<p>Small intricate matrices provide protection for small fish. Textured planters encourage coral restoration efforts by scientists.</p>
<p>But there are still <a href="https://www.mdpi.com/2076-3298/10/7/121">gaps in our knowledge</a> in how effective artificial reefs are for potential local, regional or global impact by increasing awareness of coral reef decline and positive actions.</p>
<h2>Government policy bans underwater sculptures</h2>
<p>A <a href="https://elibrary.gbrmpa.gov.au/jspui/bitstream/11017/4011/1/FINAL-Policy-on-Fish-Aggregating-Devices-and-Artificial-Reefs.pdf">new Reef Authority policy</a> on fish-aggregating devices and artificial reefs has banned the creation of new underwater sculptures on the Great Barrier Reef.</p>
<p>Its report found artificial reefs are “not compatible” with the main objective of the Marine Park Act, which is “to provide for the long-term protection and conservation of the environment, biodiversity and heritage values of the Great Barrier Reef Region”.</p>
<p>Instead of artificial reefs, the <a href="https://elibrary.gbrmpa.gov.au/jspui/bitstream/11017/3287/1/GBRMPA%20Blueprint%20for%20Resilience%20-%20Low%20Res.pdf">authority recommends initiatives</a> that include ramping up crown-of-thorns starfish control, strengthening compliance, enhanced protection of key species for reef recovery, and testing and deploying methods for reef restoration.</p>
<p>But since 2017, the community, artists, traditional owners, citizen scientists, the tourism industry and local, state and federal governments have supported <a href="https://www.dtis.qld.gov.au/tourism/funds/growing-infrastructure/museum-of-underwater-art">the Museum of Underwater Art</a>.</p>
<p>This museum has provided jobs and revenue, raised awareness and amplified <a href="https://www.dtis.qld.gov.au/tourism/funds/growing-infrastructure/museum-of-underwater-art">important messages about reef conservation</a>. </p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/young-crown-of-thorns-starfish-can-survive-heatwaves-thats-yet-more-bad-news-for-the-great-barrier-reef-215543">Young crown-of-thorns starfish can survive heatwaves. That's yet more bad news for the Great Barrier Reef</a>
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<h2>The positive impact of the reef sculpture</h2>
<p>We have been surveying the life at the Museum of Underwater Art since 2018.</p>
<p>In 2018 (pre-installation), 2020 (post-installation), 2021 and 2022, divers recorded species and abundance of individuals sighted.</p>
<p>In 2018, 12 species and 65 individual creatures were recorded at the location of the museum. The <a href="https://www.mdpi.com/2077-1312/10/11/1617">2022 survey</a> found 46 species and 365 individuals. </p>
<p>The site has also become a <a href="https://reefecologic.org/project/moua/#:%7E:text=Bringing%20life%20to%20the%20Coral%20Greenhouse&text=On%2014%20March%202021%2C%20Reef,131%20corals%20on%20treatment%20locations">reef restoration demonstration site</a>. Planting corals on underwater sculptures is an innovative method of linking art, science, tourism, education and conservation. </p>
<p>Coral gardening is a reef-restoration technique modelled on terrestrial gardening. Small cuttings of coral colonies, called fragments, are transplanted from the surrounding reef to populate the new artificial reef. The corals help to rapidly transform the art installation into a biotic location.</p>
<p>In March 2020, 131 corals were transplanted onto Taylor’s sculptures. After one year, 91.6% of the coral survived. </p>
<p>Our research on planting corals in relatively deep water of 18 metres has been challenging and innovative. Interestingly, the results are better than for shallow-water coral projects, which average an 80% survival rate after one year.</p>
<p>We also assessed tourist attitudes to the artificial reef. We found high satisfaction with the art, coral and fish observed at the site.</p>
<p>Interestingly, tourists in the Whitsundays rated <a href="https://www.researchgate.net/publication/357916065_Innovative_local_response_to_cyclone_damaged_reef_leads_to_rapid_tourism_recovery">the beauty of underwater art</a> higher than the beauty of natural reefs.</p>
<h2>Reaching new hearts</h2>
<p>Katharina Fabricious, a senior research scientist at the Australian Institute of Marine Science, <a href="https://www.abc.net.au/news/2023-05-18/museum-of-underwater-art-great-barrier-reef-ocean-sentinels/102337556">says</a>:</p>
<blockquote>
<p>Conservation needs to be communicated in a whole range of different ways, and art is reaching people that scientists sometimes cannot reach.</p>
</blockquote>
<p>The future of the Museum of Underwater Art is uncertain due to its classification as an artificial reef. The renewal or refusal of the many permits required for the artworks will be considered in the context of the new policy. It means this is the largest and possible the last underwater sculpture in the Great Barrier Reef.</p>
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<strong>
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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<img src="https://counter.theconversation.com/content/194335/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adam Smith through Reef Ecologic Pty Ltd receives funding for research from the Australian and Queensland Government. He is a voluntary Board member of the not for profit Museum of Underwater Art Pty Ltd</span></em></p><p class="fine-print"><em><span>Nathan Cook through Reef Ecologic Pty Ltd receives funding for research from the Australian and Queensland Government. </span></em></p>Reef sculptures are a form of artifical reef: man-made structures placed into an aquatic environment to mimic certain characteristics of a natural reef.Adam Smith, Adjunct Associate Professor, James Cook UniversityNathan Cook, Marine Scientist, James Cook UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2150112023-10-19T14:33:56Z2023-10-19T14:33:56ZArtificial coral reefs showing early signs they can mimic real reefs killed by climate change – new research<figure><img src="https://images.theconversation.com/files/555315/original/file-20231023-25-d9tkyu.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2780%2C1960&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/concrete-blocks-covered-orange-sponge-making-2355367201">Valda Butterworth/Shutterstock</a></span></figcaption></figure><p>Earth’s average temperature in September 2023 was 1.75°C <a href="https://www.france24.com/en/europe/20231005-last-september-was-hottest-on-record-by-extraordinary-margin-eu-monitor">above its pre-industrial baseline</a>, breaching (if only temporarily) the <a href="https://www.ipcc.ch/sr15/">1.5°C threshold</a> at which world leaders agreed to try and limit long-term warming. </p>
<p>Persistent warming at this level will make it difficult for the ocean’s coral reefs to survive. The same goes for those communities who rely on the reefs for food, to protect their coastline from storms and for other sources of income, such as tourism. Recent Intergovernmental Panel on Climate Change assessments have predicted that even if global heating is kept within the most optimistic scenarios, up to two-thirds of all coral reefs could <a href="https://www.ipcc.ch/site/assets/uploads/2018/02/WGIIAR5-CCboxes_FINAL.pdf">deteriorate over the next few decades</a>. </p>
<p>It will not be possible to restore all the reefs lost to climate change. But we are scientists who study how to preserve these habitats, and we hope that artificial structures (made from concrete or other hard materials) could replicate the complex forms of natural reefs and retain some of the benefits they provide. </p>
<p>We know artificial reefs can attract fish and host high levels of biodiversity – <a href="https://doi.org/10.3934/geosci.2022018">often similar to natural reefs</a>. This is partly due to them providing a hard surface for invertebrates like sponges and corals to grow on. Artificial reefs also offer a complex habitat of crevices, tunnels and other hiding places for species that move around a lot, such as fish, crabs and octopus.</p>
<p>Until now though, scientists were unsure if artificial reefs attracted wildlife which would otherwise live on nearby coral reefs or whether they helped support entirely new communities, enlarging existing populations. This is important, because if natural reefs do die, these artificial structures must be self-sustaining to continue benefiting species, including our own.</p>
<figure class="align-center ">
<img alt="A fisher casts a net over the camera in shallow water at sunset." src="https://images.theconversation.com/files/554252/original/file-20231017-15-nyln7z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/554252/original/file-20231017-15-nyln7z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554252/original/file-20231017-15-nyln7z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554252/original/file-20231017-15-nyln7z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554252/original/file-20231017-15-nyln7z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554252/original/file-20231017-15-nyln7z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554252/original/file-20231017-15-nyln7z.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">Millions of people worldwide rely on fish as their main source of protein.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/fisherman-net-sunset-silhouette-boat-578427937">BankZa/Shutterstock</a></span>
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<p><a href="https://doi.org/10.1007/s00227-023-04283-4">Our recent study</a> is the first to examine whether artificial reefs in the tropics can function in the same way as their naturally formed counterparts. The answer is: not yet, but these concrete structures are beginning to mimic some of the key functions of coral reefs – and they should get better at it over time. </p>
<h2>Follow the nutrients</h2>
<p>Coral reefs support lots of different species in high numbers despite growing in tropical waters low in nutrients (chemicals such as nitrates and phosphates which boost plant growth). This puzzled naturalist Charles Darwin, and it became known as <a href="https://theconversation.com/solving-darwins-paradox-why-coral-island-hotspots-exist-in-an-oceanic-desert-54719">Darwin’s Paradox</a>. We now know reefs achieve this by circulating nutrients extremely rapidly through the invertebrates, corals and fish that live on them. </p>
<p>In a healthy coral reef system, nutrients from dead animals and faeces are rapidly consumed by animals living on the reef, such as small fish or invertebrates, and these small animals are frequently eaten by larger animals. This ensures these nutrients cannot accumulate and so they remain at low levels, preventing algae from overgrowing and smothering the reef. </p>
<p>If artificial reefs perform a similar function to natural reefs then we would expect them to rapidly process nutrients entering the system and keep overall nutrient levels low too. This would indicate they are also highly productive ecosystems, similarly capable of supporting diverse and abundant wildlife even if many natural reefs die.</p>
<p>We tried to make an accurate comparison of natural and artificial reefs by comparing nutrient levels and how they are stored between the two. </p>
<h2>From concrete to corals</h2>
<p>Our study was conducted in north Bali, Indonesia. A local non-profit, <a href="https://northbalireefconservation.com/">North Bali Reef Conservation</a>, which Zach co-founded, has been making artificial reefs for the last six years with the help of international volunteers and local fishers who use their boats to drop them offshore. </p>
<p>While over 15,000 reefs have been deployed so far, they only cover around 2 hectares – roughly the size of two football pitches.</p>
<p>But these structures are beginning to show signs of functioning like coral reef communities. In water we extracted from just under the sand near the artificial reefs we found high levels of phosphates – evidence of a large number of fish excreting. And in water samples from above the sediment, levels of all the nutrients we measured were low and similar to those recorded on natural reefs, indicating the artificial reef was rapidly recycling these nutrients.</p>
<p>However, the sediment around the concrete structures we tested appeared to be storing less carbon than that surrounding the natural reefs. We think the difference may be related to the relative abundance of invertebrate species such as hydroids (plant-like relatives of corals which feed by sifting detritus from seawater). These were common on the natural reefs we studied, but were only found in small, but increasing numbers on the artificial reefs. We think, as more of these species colonise the concrete over time, the reefs will function even more like their natural counterparts. </p>
<p>The study offers some hope that over time, artificial reefs can mimic more of the processes maintained by natural reefs. Our findings are an early indication that artificial reefs may be able to support local communities affected by reefs lost to climate change. </p>
<p>The climate threat to coral reefs will not be solved by artificial reefs. Only rapidly eliminating emissions of greenhouse gases can preserve a future for these ecosystems. But our research indicates that, where reefs have already been lost, through pollution, destructive fishing or coastal development, it may be possible to restore some of the lost benefits with artificial structures.</p>
<p>Our study suggests it can take up to five years for artificial reefs to begin functioning like coral reefs, so these recovery programmes must begin right away.</p>
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<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">
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<p class="fine-print"><em><span>Rick Stafford receives funding from the Earthwatch Institute.</span></em></p><p class="fine-print"><em><span>Zach Boakes receives funding from the Earthwatch Institute. He is co-founder of the non-governmental organisation North Bali Reef Conservation.</span></em></p>Concrete structures can recreate the complex forms of reefs, offering refuge to wildlife.Rick Stafford, Professor of Marine Biology and Conservation, Bournemouth UniversityZach Boakes, PhD Candidate in Conservation, Bournemouth UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2155432023-10-18T19:06:09Z2023-10-18T19:06:09ZYoung crown-of-thorns starfish can survive heatwaves. That’s yet more bad news for the Great Barrier Reef<figure><img src="https://images.theconversation.com/files/554464/original/file-20231018-23-teqay1.jpg?ixlib=rb-1.1.0&rect=0%2C27%2C3642%2C2697&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>You might not realise it, but the infamous crown-of-thorns starfish is native to coral reefs throughout the Indo-Pacific – including the Great Barrier Reef. When they’re fully grown, these large, thorn-covered starfish dine on hard coral polyps.</p>
<p>That’s fine when their populations are small. They can play an important role in keeping reefs healthy by eating fast-growing branching corals and clearing space for slower-growing coral species.</p>
<p>But when their populations surge, they can decimate coral reefs – and strip habitat for the myriad species relying on them. </p>
<p>Our coral reefs are already suffering from marine heatwaves, pollution and overfishing. Crown-of-thorns outbreaks can push reefs over the edge. </p>
<p>But can these starfish survive the marine heatwaves now striking the oceans more and more regularly? To find out, we worked out what temperatures the starfish could handle. </p>
<p><a href="https://doi.org/10.1111/gcb.16946">Our results suggest</a> baby crown-of-thorns starfish are, unfortunately, very tolerant of warmer water. It’s more bad news for our sick reefs. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/554461/original/file-20231018-21-446vn8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="bleached coral reef near the surface of the sea" src="https://images.theconversation.com/files/554461/original/file-20231018-21-446vn8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/554461/original/file-20231018-21-446vn8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554461/original/file-20231018-21-446vn8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554461/original/file-20231018-21-446vn8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554461/original/file-20231018-21-446vn8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554461/original/file-20231018-21-446vn8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554461/original/file-20231018-21-446vn8.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">Coral bleaching can actually be good for crown-of-thorns starfish.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Keystone predators of the reef</h2>
<p>At up to 80 centimetres across, crown-of-thorns starfish are one of the largest invertebrates on coral reefs. They are named after their toxic spines. </p>
<p>Their large central body houses a particularly large stomach. To eat, they force their stomachs out of their mouths to cover the coral underneath their body. Once wrapped around the coral, enzymes released from the stomach liquefies the coral’s soft tissues and absorbs the nutrients – leaving only the skeleton behind. </p>
<p>These starfish have evolved to become keystone predators. That is, relative to their population, they have a disproportionately large ability to control how abundant other species are. </p>
<p>During an outbreak, their swarms can eat up to 95% of hard corals on some reefs. When this happens, not only are coral species hard hit, but the animals dependent on them as well. </p>
<p>When the conditions are right, these starfish can go from a <a href="https://portlandpress.com/emergtoplifesci/article/6/1/67/230852/Crown-of-thorns-starfish-life-history-traits">very low abundance</a> of one per hectare to upwards of a thousand in a short period of time. </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>They are remarkably good at reproducing. The females can spawn hundreds of millions of eggs and the males can put out <a href="https://link.springer.com/article/10.1007/s00227-016-3009-5">10 trillion sperm</a> into the water during the breeding season. </p>
<p>Not only that, but the larvae can <a href="https://www.sciencedirect.com/science/article/pii/S0025326X16310840">adjust their bodies</a> depending on the availability of food. When food is low, the arms of the larvae grow longer. These arms have bands of little hairs used to capture food. The longer these bands are, the more food they can capture. </p>
<p>Despite their ability to breed like rabbits, crown-of-thorns populations go through boom and bust. Why? We don’t fully know, even after decades of intensive research and enormous expenditure. Leading theories include a boom following nutrient run-off from rivers and the removal of predatory fish. Other important predators such as the <a href="https://www.barrierreef.org/the-reef/animals/giant-triton">giant triton shell</a> (which eats adults) and the <a href="https://link.springer.com/article/10.1007/s00338-023-02364-w">red decorator crab</a> (which eats juveniles). </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/554245/original/file-20231017-29-a0uhr1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An adult crown-of-thorns starfish eating coral" src="https://images.theconversation.com/files/554245/original/file-20231017-29-a0uhr1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/554245/original/file-20231017-29-a0uhr1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554245/original/file-20231017-29-a0uhr1.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554245/original/file-20231017-29-a0uhr1.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554245/original/file-20231017-29-a0uhr1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554245/original/file-20231017-29-a0uhr1.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554245/original/file-20231017-29-a0uhr1.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">These starfish cover coral with their stomachs to eat it.</span>
<span class="attribution"><span class="source">Shawna Foo</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/theres-a-hidden-source-of-excess-nutrients-suffocating-the-great-barrier-reef-we-found-it-214364">There's a hidden source of excess nutrients suffocating the Great Barrier Reef. We found it</a>
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<h2>What we did and what we found</h2>
<p>Virtually all research on crown-of-thorns starfish has focused on larval or adult stages, with little to no attention to juveniles, which are difficult to study. </p>
<p>The juveniles start their life on the reef as algae eaters. Our <a href="https://royalsocietypublishing.org/doi/full/10.1098/rsbl.2019.0849">previous research</a> has shown they don’t have to grow up fast. They can remain herbivores for many years when there’s not enough coral to eat and feast on the algae growing on the skeletons of coral killed by heatwaves. </p>
<p>These Peter Pan-like juveniles can build up hidden in the reef over many years. But how do they cope with heat? </p>
<p>Our experiments revealed young starfish can survive tremendous heatwaves, well above the temperatures needed to bleach or kill coral. Coral can bleach or die when water gets 1–3°C warmer, depending on how long the heat lasts. But the starfish had much greater tolerance – almost three times the heat needed to bleach coral.</p>
<p>All of them survived in coral bleaching conditions – four consecutive weeks of temperatures 1°C above the average maximum temperatures for the sea surface in summer, as well as eight consecutive weeks (enough for mass death of corals) and even 12 weeks – extreme conditions well past what coral can survive. </p>
<p>Over the course of the experiment, the juveniles could handle waters up to 34–36°C.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/554244/original/file-20231017-15-8q144e.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A juvenile crown-of-thorns starfish eating algae from coral rubble." src="https://images.theconversation.com/files/554244/original/file-20231017-15-8q144e.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/554244/original/file-20231017-15-8q144e.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=467&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554244/original/file-20231017-15-8q144e.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=467&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554244/original/file-20231017-15-8q144e.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=467&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554244/original/file-20231017-15-8q144e.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=586&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554244/original/file-20231017-15-8q144e.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=586&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554244/original/file-20231017-15-8q144e.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=586&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">These starfish eat algae when young and coral when they’re fully grown.</span>
<span class="attribution"><span class="source">Monique Webb and Matthew Clements</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>More bad news for coral reefs</h2>
<p>This is not good news for our reefs. Warming waters may actually make life easier for a major predator of coral. </p>
<p>Even if the coral-eating adults decline as their coral prey dies back, their young can wait patiently for the right moment to develop into predators able to devour corals just as they begin to recover. </p>
<p>This discovery may help explain why adult crown-of-thorns starfish outbreaks can occur so suddenly. </p>
<p>For years, we’ve suspected the acceleration of outbreaks was linked to predator removal or a build-up of nutrients in the water. </p>
<p>Now we have evidence that coral bleaching and death could actually aid the juvenile crown-of-thorns starfish – and that the heat tolerance of juveniles could add even more pressure to struggling reefs. </p>
<p>Ultimately, the only real solution is to rapidly reduce greenhouse gas emissions.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/could-marine-cloud-brightening-reduce-coral-bleaching-on-the-great-barrier-reef-214308">Could 'marine cloud brightening' reduce coral bleaching on the Great Barrier Reef?</a>
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<img src="https://counter.theconversation.com/content/215543/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>For this project, Matt Clements received funding for a PhD scholarship from the University of Sydney and partial support from the Ian Potter Foundation crown-of-thorns starfish grants through the Lizard Island Research Foundation.</span></em></p><p class="fine-print"><em><span>For this project, Maria Byrne received partial support from the Ian Potter Foundation crown-of-thorns starfish grants through the Lizard Island Research Foundation. </span></em></p>Nature’s ultimate coral predator could benefit from climate change by surviving heatwaves and lie in wait for the right moment to feast on the reef.Matt Clements, PhD Student, University of SydneyMaria Byrne, Professor of Developmental & Marine Biology, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2110882023-10-12T21:13:09Z2023-10-12T21:13:09ZHow clouds protect coral reefs, but will not be enough to save them from us<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/how-clouds-protect-coral-reefs-but-will-not-be-enough-to-save-them-from-us" width="100%" height="400"></iframe>
<p>Coral reefs are vital <a href="https://www.noaa.gov/education/resource-collections/marine-life/coral-reef-ecosystems">ecosystems</a> for people and coastal communities. They provide <a href="https://www.coast.noaa.gov/states/fast-facts/coral-reefs.html">food and livelihoods</a> and protect coastlines from storms, contribute to local economies and preserve cultural heritage.</p>
<p>However, warming ocean temperatures as a result of human-made climate change present considerable risks to the reefs. The recent rise in <a href="https://doi.org/10.1038/nature21707">coral bleaching</a> all over the world is the most visible impact.</p>
<p>But what is <a href="https://oceanservice.noaa.gov/facts/coral_bleach.html">coral bleaching</a>? Coral bleaching is a phenomenon that occurs when the white skeleton of the corals becomes visible after the microalgae that live inside their translucent tissues are expelled. </p>
<p>Even though coral reefs can <a href="https://reefresilience.org/stressors/bleaching/bleaching-biology/">recover</a> from bleaching events, the process, much like the regrowth of a forest following a windstorm or wildfire, requires a considerable amount of time. And, as our research has shown, an appreciation of the role of cloud cover.</p>
<h2>Relief in the clouds</h2>
<p>Although coral bleaching is generally linked only to ocean temperatures, the process itself is a product of the interaction between high <a href="https://reefresilience.org/stressors/bleaching/bleaching-biology/">temperatures and sunlight levels in a given area</a>. </p>
<p>If the temperatures are high enough, the coral and microalgae become more light-sensitive. When combined with <a href="https://doi.org/10.3389/fmicb.2014.00422">excessive sunlight</a>, this sensitivity harms the microalgae which, in turn, results in the production of chemical compounds called <a href="https://doi.org/10.1242/jeb.009597">reactive oxygen species</a>. These compounds are harmful to many species and in the case of reefs cause the coral to expel its microalgae.</p>
<p>In the same way that clouds protect us from harmful exposure to UV rays, clouds also provide a protective barrier for the world’s coral reefs. Field studies of coral bleaching events in <a href="https://www.int-res.com/abstracts/meps/v222/p209-216/">French Polynesia</a> and in the <a href="https://doi.org/10.1038/s41598-019-40150-3">Republic of Kiribati</a> found that periods of cloudiness may have reduced the bleaching severity and extent. </p>
<p>Climate change is projected to kill off most of the world’s coral reefs, even in scenarios with only <a href="http://dx.doi.org/10.1038/nclimate1674">1.5 C</a> of global warming. Yet, to date, most analysis has only considered the effect of temperature. Could incorporating clouds change the forecast?</p>
<h2>Considering cloudiness</h2>
<p>In order to understand how cloudiness might influence the response of coral reefs to climate change, <a href="https://doi.org/10.1371/journal.pclm.0000090">our recent study</a> used a <a href="https://doi.org/10.1371/journal.pone.0281719">global historical database</a> containing almost 38,000 coral bleaching reports to train an algorithm that estimates bleaching severity based on incoming light and temperature stress. </p>
<p>Our algorithm was then <a href="https://www.climateneutralgroup.com/en/news/five-future-scenarios-ar6-ipcc/">applied to four different future climate scenarios</a> on the world’s coral reefs to assess if and when bleaching conditions would become too frequent for reefs to recover. The results indicate that under a low emissions scenario, increased cloudiness would indeed have an effect on the coral bleaching conditions. This means that corals would have more time to recover from the impacts of rising temperatures and improve their resilience. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/coral-reefs-how-climate-change-threatens-the-hidden-diversity-of-marine-ecosystems-211007">Coral reefs: How climate change threatens the hidden diversity of marine ecosystems</a>
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<p>However, even under a low carbon emission scenario, this extra time will not be enough to prevent more than 70 per cent of global reefs experiencing frequent bleaching conditions with not enough time in between to fully recover.</p>
<p>This highlights the severity of the coral bleaching crisis caused by thermal stress and the limitations of relying solely on cloudiness as a protective mechanism. Simply put, while clouds can offer some relief to corals, they cannot mitigate the long-term consequences of climate change when the sea surface temperature becomes too high.</p>
<h2>Clear implications</h2>
<p>Cloud cover may offer temporary relief to coral reefs by delaying the adverse environmental conditions responsible for coral bleaching. However, that seems to be partially true only in the lowest emission scenario which would be possible only if we dramatically cut greenhouse gas emissions.</p>
<p>Without doing that, dangerously frequent bleaching conditions are unavoidable and reefs will continue to be threatened even if we cut down emissions now. Moreover, we also need to get serious about habitat and biodiversity protection <a href="https://www.epa.gov/coral-reefs/threats-coral-reefs">to increase resilience</a>. </p>
<p>Only by doing this could coral reefs stand a chance at surviving the increasing pressures of climate change. Any other approach has its head in the clouds.</p><img src="https://counter.theconversation.com/content/211088/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Pedro C. González Espinosa receives funding from the Nippon Foundation Ocean Nexus, School of Resource and Environmental Management (REM), Simon Fraser University (SFU). </span></em></p><p class="fine-print"><em><span>Simon Donner receives funding from Natural Sciences and Engineering Research Council and the Social Sciences and Humanities Research Council.</span></em></p>Understanding how both cloud cover and temperature work to promote coral bleaching provides valuable insight into how reefs will change over various climate scenarios.Pedro C. González Espinosa, Postdoctoral Reserach Fellow, The School of Resource and Environmental Management, Simon Fraser UniversitySimon Donner, Professor, Department of Geography, University of British ColumbiaLicensed 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>
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<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>
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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>
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<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/2124602023-09-14T20:04:44Z2023-09-14T20:04:44ZSeaweed is taking over coral reefs. But there’s a gardening solution – sea-weeding<figure><img src="https://images.theconversation.com/files/545914/original/file-20230901-21-1ry9dp.jpeg?ixlib=rb-1.1.0&rect=0%2C3%2C2044%2C1361&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Roxana Caha</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p>In the early 1990s, marine researchers in the Caribbean found <a href="https://www.science.org/doi/abs/10.1126/science.265.5178.1547">something alarming</a>. On reef after reef, corals were dying off – and seaweed was growing in their place. </p>
<p>Since then, this pattern has been observed on reefs <a href="https://gcrmn.net/2020-report-v1-2023/">around the world</a>: as corals die, seaweed takes over.</p>
<p>Once seaweed gets a foothold, it’s hard for coral to compete. These large, fleshy algae can quickly come to dominate. As the oceans heat up and reefs degrade, the trend is expected to accelerate. Former coral reefs will become dominated by seaweed instead, with cascading damage to reef ecosystems. </p>
<p>This shift hasn’t happened widely on the Great Barrier Reef – yet. But there are <a href="https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/eap.2008">worrying signs</a> of seaweed takeover on some reefs, including those fringing Yunbenun (Magnetic Island). </p>
<p>We wondered – what if you could help corals by weeding out intruding seaweed? In our <a href="https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2664.14502">new research</a>, we found sea-weeding actually worked, giving coral time to recover. </p>
<p>Of course, this is a stopgap measure. It’s designed to buy time while we tackle the main threats to the world’s largest reef system – notably, climate change. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/548205/original/file-20230914-21-e4lupr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Bagging seaweed" src="https://images.theconversation.com/files/548205/original/file-20230914-21-e4lupr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548205/original/file-20230914-21-e4lupr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=629&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548205/original/file-20230914-21-e4lupr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=629&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548205/original/file-20230914-21-e4lupr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=629&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548205/original/file-20230914-21-e4lupr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=790&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548205/original/file-20230914-21-e4lupr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=790&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548205/original/file-20230914-21-e4lupr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=790&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 citizen scientist bags the weeded macroalgae for weighing.</span>
<span class="attribution"><span class="source">Miranda Fittock</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>How can seaweed take over?</h2>
<p>Corals don’t like hot water, sediment or an overload of nutrients. So when there’s a mass bleaching or coral death event after a marine heatwave or cyclone, there’s empty space on the reef. </p>
<p>Seaweeds are similar to weeds in a garden. They can colonise quickly, grow fast and tall, soaking up sunlight and competing directly with surviving corals for light and space. </p>
<p>Once these tough algae establish, corals struggle to come back. Then there are feedback loops which can further prevent coral return – coral larvae are <a href="https://www.int-res.com/abstracts/meps/v362/p129-137/">put off</a> by chemicals emitted by seaweed. Seaweed growth <a href="https://www.taylorfrancis.com/chapters/edit/10.1201/9781420065756-4/effects-benthic-algae-replenishment-corals-implications-resilience-coral-reefs-chico-birrell-laurence-mccook-bette-willis-guillermo-diaz-pulido">takes the space</a> where coral larvae could have settled. And the health of adult corals can be hit by algae just living nearby. It’s safe to say coral and algae are not best friends. </p>
<hr>
<p>
<em>
<strong>
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>
</strong>
</em>
</p>
<hr>
<p>You might wonder why nature doesn’t even the balance. At Yunbenun, the main genus of seaweed is <em>Sargassum</em>, most famous for their <a href="https://www.theguardian.com/environment/2023/mar/07/great-atlantic-sargassum-belt-seaweed-visible-from-space">massive blooms</a> in the Sargasso Sea. The problem is, not many fish like the taste. When <em>Sargassum</em> is fully grown, it’s <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0202273">especially unpalatable</a> to herbivorous fish. </p>
<p>Many fish will actively <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/j.1461-0248.2010.01581.x?casa_token=gNVQVHj9M8QAAAAA:lhpsH_cw-h1ZhmoVkyRwBPQSGgBS4ROA-kXgE4HJYX2TzhaImy-F8hGhpHNmvy_yERfsqm5KbLXdlnI">avoid areas</a> with long, dense growth of seaweed for fear of predators hiding among the foliage. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/546110/original/file-20230904-31-jdtxc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="scuba diver measuring seaweed" src="https://images.theconversation.com/files/546110/original/file-20230904-31-jdtxc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/546110/original/file-20230904-31-jdtxc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/546110/original/file-20230904-31-jdtxc4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/546110/original/file-20230904-31-jdtxc4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/546110/original/file-20230904-31-jdtxc4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/546110/original/file-20230904-31-jdtxc4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/546110/original/file-20230904-31-jdtxc4.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 reefs at Yunbenun (Magnetic Island) are dominated by macroalgae.</span>
<span class="attribution"><span class="source">Victor Huertas-Martin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Weeding the sea</h2>
<p>So if grazing fish won’t eat the problem, and urchins aren’t very abundant, it’s up to us. We set about testing sea-weeding, where you dive down and cut back stands of macroalgae. Would the corals bounce back? </p>
<p>The process is just like weeding a garden, but underwater. You dive down, yank fronds of seaweed off the seafloor and dispose them back on shore. It’s labour intensive, but simple. We were aided in weeding by citizen scientists through <a href="https://earthwatch.org.au/expeditions/recovery-of-the-great-barrier-reef">Earthwatch Institute</a>. </p>
<p>It took three years, and the removal of three tonnes of seaweed, but it worked. In the areas we’d weeded (300m², or about 1% of the seafloor at our study site) twice or three times a year, the coral had made a spectacular recovery. Corals now covered between 1.5 to six times the area they had before. </p>
<p>After the coral returned, seaweed has been growing back less and less. Seaweed originally covered 80% of the seafloor, but now covers less than 40%. That suggests it might need only a few years of effort to suppress the seaweed and push the coral ecosystem toward recovery. </p>
<p>Importantly, the diversity of coral species increased too – and that means weeding isn’t favouring any single coral species.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/546111/original/file-20230904-21-pte30t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="before and after sea weed removal" src="https://images.theconversation.com/files/546111/original/file-20230904-21-pte30t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/546111/original/file-20230904-21-pte30t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=263&fit=crop&dpr=1 600w, https://images.theconversation.com/files/546111/original/file-20230904-21-pte30t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=263&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/546111/original/file-20230904-21-pte30t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=263&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/546111/original/file-20230904-21-pte30t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=330&fit=crop&dpr=1 754w, https://images.theconversation.com/files/546111/original/file-20230904-21-pte30t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=330&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/546111/original/file-20230904-21-pte30t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=330&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Left: a section of weeded reef in October 2020. Right: the same section of reef in October 2021, showing significant coral growth.</span>
<span class="attribution"><span class="source">Author provided</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>We disposed of the seaweed in a local school’s organic compost heap. While not part of this project, there is promising new research showing macroalgae like <em>Sargassum</em> could be a <a href="https://www.sciencedirect.com/science/article/pii/S0048969720322622">carbon sink</a>. Seaweed has many uses, ranging from <a href="https://www.sciencedirect.com/science/article/pii/S2213343721008721">bio-plastics</a>, fertiliser or <a href="https://link.springer.com/article/10.1007/s12155-021-10382-1">biofuels</a>. If the economics stack up, removing mature macroalgae could provide a win-win for reef and climate health – even if it’s only small scale. </p>
<h2>Where would this approach be most useful?</h2>
<p>On the Great Barrier Reef, the reefs <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0279699">most prone</a> to seaweed takeover are those near to shore. These are, as you’d expect, also the most accessible and the ones most often visited by tourists. </p>
<p>If you were going to use this technique more widely, it would make sense, therefore, to focus on nearshore reefs. They’re economically important for industries like tourism and fishing. </p>
<p>At present, there’s a lot of research being done on high-tech interventions such as breeding corals to tolerate hotter water, or brightening clouds. What we hope to show is the equal value of testing low-tech, low-cost methods which can achieve scale by harnessing citizen science volunteers and community programs. This has the added advantage of building public support and giving concerned citizens a clear way to help. It could be useful not only in Australia, but on island nations in the Pacific with limited resources.</p>
<p>By our estimates, the cost – around A$104,000 per hectare – is a fraction of other reef restoration techniques, which have a <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/rec.12977">median cost</a> of about $616,000 per hectare, ranging all the way up to $6.2 million per hectare. </p>
<p>This isn’t a silver bullet. We have no reef restoration or management approaches able to keep our reefs alive if we don’t tackle the big issues – hotter, more acidic seas brought about by climate change, as well as nutrient runoff and other threats. </p>
<p>So what role could sea-weeding have? Even if we manage to significantly cut emissions globally in the coming decades, there’s so much CO₂ already in the atmosphere that reefs will keep deteriorating. </p>
<p>That means there could well be a role for this approach. This low-tech but rapidly effective technique could help keep corals alive while we work for decisive action on climate change. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/accelerated-evolution-and-automated-aquaculture-could-help-coral-weather-the-heat-209388">Accelerated evolution and automated aquaculture could help coral weather the heat</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/212460/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hillary Smith receives funding from a partnership between Earthwatch Institute and Mitsubishi Corporation, as well as the National Geographic Society, the British Ecological Society, the Reef HQ Volunteer Association, and the Women Diver Hall of Fame. She is a 2019 National Geographic Explorer, and is affiliated with James Cook University and the University of New South Wales.</span></em></p><p class="fine-print"><em><span>David Bourne receives funding from a partnership between Earthwatch Institute and Mitsubishi Corporation. He is affiliated with James Cook University and the Australian Institute of Marine Science. </span></em></p>Many researchers are exploring high-tech ways to help reefs survive the climate crisis. But low-tech solutions like manually pulling out seaweed have a place too.Hillary Smith, Senior Research Officer, James Cook UniversityDavid Bourne, Professor of Marine Biology, James Cook UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2129242023-09-06T12:26:36Z2023-09-06T12:26:36ZInvasive species cause billions of dollars in damage worldwide: 4 essential reads<p>Invasive species – including plants, animals and fish – cause heavy damage to crops, wildlife and human health worldwide. Some prey on native species; other out-compete them for space and food or spread disease. A new United Nations report estimates the losses generated by invasives at <a href="https://zenodo.org/record/8314303">more than US$423 billion yearly</a> and shows that these damages have at least quadrupled in every decade since 1970.</p>
<p>Humans regularly move animals, plants and other living species from their home areas to new locations, either accidentally or on purpose. For example, they may import plants from faraway locations to <a href="https://theconversation.com/invasive-grasses-are-fueling-wildfires-across-the-us-126574">raise as crops</a> or bring in a nonnative animal to <a href="https://theconversation.com/everyone-agreed-cane-toads-would-be-a-winner-for-australia-19881">prey on a local pest</a>. Other invasives <a href="https://theconversation.com/the-invasive-emerald-ash-borer-has-destroyed-millions-of-trees-scientists-aim-to-control-it-with-tiny-parasitic-wasps-158403">hitch rides in cargo</a> or <a href="https://theconversation.com/ballast-water-management-is-reducing-the-flow-of-invasive-species-into-the-great-lakes-190880">ships’ ballast water</a>.</p>
<p>When a species that is not native to a particular area becomes established there, reproducing quickly and causing harm, it has become invasive. These recent articles from The Conversation describe how several invasive species are causing economic and ecological harm across the U.S. They also explain steps that people can take to avoid contributing to this urgent global problem.</p>
<h2>1. The best intentions: Callery pear trees</h2>
<p>Many invasive species were introduced to new locations because people thought they would be useful. One example that’s widely visible across the U.S. Northeast, Midwest and South is the Callery pear (<em>Pyrus calleryana</em>), a flowering tree that botanists brought to the U.S. from Asia more than 100 years ago. </p>
<p>Horticulturists loved the Callery pear for landscaping and wanted to produce trees that all grew and bloomed in the same way. As University of Dayton plant ecologist <a href="https://scholar.google.com/citations?user=uRA-SZ0AAAAJ&hl=en&oi=sra">Ryan W. McEwan</a> explained, they created identical clones from cuttings of trees with the desired characteristics – a process called grafting. Unlike some trees, a Callery pear can’t fertilize its flowers with its own pollen, so plant experts thought it wouldn’t spread.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/1i8hL2mhCpM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Missouri state foresters explain why Callery pear trees became so popular and the problems they cause.</span></figcaption>
</figure>
<p>However, “as horticulturalists tinkered with Callery pears to produce new versions, they made the individuals different enough to <a href="https://theconversation.com/once-the-callery-pear-tree-was-landscapers-favorite-now-states-are-banning-this-invasive-species-and-urging-homeowners-to-cut-it-down-198724">escape the fertilization barrier</a>,” McEwan wrote. As wind and birds spread the trees’ seeds, wild populations of the trees became established and started crowding out native species. </p>
<p>Today, Callery pear trees are such scourges that several states have banned them. Others are paying residents to cut them down and replace them with native plants. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/once-the-callery-pear-tree-was-landscapers-favorite-now-states-are-banning-this-invasive-species-and-urging-homeowners-to-cut-it-down-198724">Once the Callery pear tree was landscapers' favorite – now states are banning this invasive species and urging homeowners to cut it down</a>
</strong>
</em>
</p>
<hr>
<h2>2. Tiny organisms, big impacts: Zebra and quagga mussels</h2>
<p>Invasive species don’t have to be large to cause outsized damage. Zebra and quagga mussels – shellfish the size of a fingernail – invaded the Great Lakes in the 1980s, clogging water intake pipes and out-competing native mollusks for food. Now they’re spreading west via rivers, lakes and bays, threatening waters all the way to the Pacific coast and Alaska.</p>
<p>As Rochester Institute of Technology environmental historian <a href="https://www.researchgate.net/scientific-contributions/Christine-Keiner-2071802254">Christine Keiner</a> wrote, it took several decades for the U.S. and Canada to regulate ships’ management of their ballast water tanks, which was the route by which the mussels were introduced to North America. </p>
<p>“Now, however, other human activities are increasingly contributing to harmful freshwater introductions – and with shipping regulated, the main culprits are <a href="https://theconversation.com/the-westward-spread-of-zebra-and-quagga-mussels-shows-how-tiny-invaders-can-cause-big-problems-185286">thousands of private boaters and anglers</a>,” Keller wrote. Limiting the destructive impacts of invasive species “requires scientific, technological and historical knowledge, political will and skill to persuade the public that everyone is part of the solution.”</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/546519/original/file-20230905-29-ibkd25.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Infographic showing locations on a motorboat to check for invasive mussels." src="https://images.theconversation.com/files/546519/original/file-20230905-29-ibkd25.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/546519/original/file-20230905-29-ibkd25.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/546519/original/file-20230905-29-ibkd25.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/546519/original/file-20230905-29-ibkd25.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/546519/original/file-20230905-29-ibkd25.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/546519/original/file-20230905-29-ibkd25.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/546519/original/file-20230905-29-ibkd25.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Many states require boaters to clean and dry their boats after use to avoid spreading zebra and quagga mussels.</span>
<span class="attribution"><a class="source" href="https://neinvasives.com/stop-aquatic-hitchhikers">Nebraska Invasive Species Program</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-westward-spread-of-zebra-and-quagga-mussels-shows-how-tiny-invaders-can-cause-big-problems-185286">The westward spread of zebra and quagga mussels shows how tiny invaders can cause big problems</a>
</strong>
</em>
</p>
<hr>
<h2>3. Threatening entire ecosystems: Lionfish</h2>
<p>When an invasive species is especially successful at spreading and reproducing, it can threaten the health of entire ecosystems. Consider the Pacific red lionfish (<em>Pterois volitans</em>), which has spread throughout the Caribbean and now is <a href="https://theconversation.com/invasive-lionfish-have-spread-south-from-the-caribbean-to-brazil-threatening-ecosystems-and-livelihoods-199229">moving south along Brazil’s coast</a>. </p>
<p>Lionfish thrive in many ocean habitats, from coastal mangrove forests to deepwater reefs, and they prey on numerous smaller fish species. In the Caribbean, they have reduced the number of small juvenile fish on reefs by up to 80% within as little as five weeks. </p>
<p>“Scientists and environmental managers widely agree that the lionfish invasion in Brazil is a potential ecological disaster,” warned Brazilian marine ecologist <a href="https://scholar.google.com.au/citations?user=_ArEYYMAAAAJ&hl=en">Osmar J. Luiz</a> of Charles Darwin University. “Brazil’s northeast coast, with its rich artisanal fishing activity, stands on the front line of this invasive threat.”</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1692994189099700515"}"></div></p>
<p>Although the Brazilian government was slow to address the lionfish threat, Luiz asserted that “with strategic, swift action and international collaboration, it can mitigate the impacts of this invasive species and safeguard its marine ecosystems.” That will require many techniques, from recruiting coastal residents to monitor for the invaders to tracking lionfish subpopulations using DNA analysis. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/invasive-lionfish-have-spread-south-from-the-caribbean-to-brazil-threatening-ecosystems-and-livelihoods-199229">Invasive lionfish have spread south from the Caribbean to Brazil, threatening ecosystems and livelihoods</a>
</strong>
</em>
</p>
<hr>
<h2>4. The value of acting locally</h2>
<p>Public awareness is critical for stemming the spread of many invasive plants and animals. That can involve actions as simple as cleaning your shoes and socks after a hike. </p>
<p>“Certain species of nonnative invasive plants produce seeds <a href="https://theconversation.com/those-seeds-clinging-to-your-hiking-socks-may-be-from-invasive-plants-heres-how-to-avoid-spreading-them-to-new-locations-195697">designed to attach to unsuspecting animals or people</a>. Once affixed, these sticky seeds can be carried long distances before they fall off in new environments,” explains Boise State University ecology Ph.D. candidate <a href="https://scholar.google.com/citations?user=nmAblPEAAAAJ&hl=en&oi=ao">Megan Dolman</a>. </p>
<p>Research shows that recreational trails promote the introduction of invasive plant species into natural and protected areas, including national parks and scenic trails.</p>
<p><div data-react-class="InstagramEmbed" data-react-props="{"url":"https://www.instagram.com/p/CkgNbwptsgc/?utm_source=ig_web_copy_link\u0026igshid=MzRlODBiNWFlZA==","accessToken":"127105130696839|b4b75090c9688d81dfd245afe6052f20"}"></div></p>
<p>In her research, Dolman found that few Appalachian Trail hikers were aware of the risk of carrying invasive plant seeds on their shoes or socks, so they typically did not take steps such as cleaning their gear before and after hiking. By knowing about invasive species in their areas and ways to manage them, people can help protect special places and keep invasive species from spreading.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/those-seeds-clinging-to-your-hiking-socks-may-be-from-invasive-plants-heres-how-to-avoid-spreading-them-to-new-locations-195697">Those seeds clinging to your hiking socks may be from invasive plants – here's how to avoid spreading them to new locations</a>
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</em>
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<p><em>Editor’s note: This story is a roundup of articles from The Conversation’s archives.</em></p><img src="https://counter.theconversation.com/content/212924/count.gif" alt="The Conversation" width="1" height="1" />
According to a new UN report, invasive species do more than US$423 billion in damage worldwide every year. Four articles explore examples, from mollusks to poisonous fish.Jennifer Weeks, Senior Environment + Cities Editor, The ConversationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2114312023-08-30T20:36:24Z2023-08-30T20:36:24ZWe studied more than 1,500 coastal ecosystems - they will drown if we let the world warm above 2°C<figure><img src="https://images.theconversation.com/files/545179/original/file-20230829-15-v3if80.jpeg?ixlib=rb-1.1.0&rect=46%2C20%2C3368%2C2826&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Simon Albert</span></span></figcaption></figure><p>Much of the world’s natural coastline is protected by living habitats, most notably mangroves in warmer waters and tidal marshes closer to the poles. These ecosystems support fisheries and wildlife, absorb the impact of crashing waves and clean up pollutants. But these vital services are threatened by global warming and rising sea levels. </p>
<p>Recent research has shown wetlands can respond to sea level rise by building up their root systems, <a href="https://theconversation.com/rising-seas-allow-coastal-wetlands-to-store-more-carbon-113020">pulling carbon dioxide from the atmosphere in the process</a>. Growing recognition of the potential for this “blue” carbon sequestration is driving mangrove and tidal marsh restoration projects. </p>
<p>While the resilience of these ecosystems is impressive, it is not without limits. Defining the upper limits to mangrove and marsh resilience under accelerating sea level rise is a topic of great interest and considerable debate. </p>
<p>Our new research, <a href="https://www.nature.com/articles/s41586-023-06448-z">published today in the journal Nature</a>, analyses the vulnerability and exposure of mangroves, marshes and coral islands to sea level rise. The results underscore the critical importance of keeping global warming within 2 degrees of the pre-industrial baseline. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/542967/original/file-20230816-19-44orpq.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo showing uprooted trees in tropical waters of the Solomon Islands." src="https://images.theconversation.com/files/542967/original/file-20230816-19-44orpq.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/542967/original/file-20230816-19-44orpq.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=215&fit=crop&dpr=1 600w, https://images.theconversation.com/files/542967/original/file-20230816-19-44orpq.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=215&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/542967/original/file-20230816-19-44orpq.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=215&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/542967/original/file-20230816-19-44orpq.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=271&fit=crop&dpr=1 754w, https://images.theconversation.com/files/542967/original/file-20230816-19-44orpq.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=271&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/542967/original/file-20230816-19-44orpq.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=271&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Coral islands are contracting, causing habitat loss in the Solomon Islands.</span>
<span class="attribution"><span class="source">Simon Albert</span></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/not-waving-drowning-why-keeping-warming-under-1-5-is-a-life-or-death-matter-for-tidal-marshes-187540">Not waving, drowning: why keeping warming under 1.5℃ is a life-or-death matter for tidal marshes</a>
</strong>
</em>
</p>
<hr>
<h2>What we did</h2>
<p>We pulled together all the available evidence on how mangroves, tidal marshes and coral islands respond to sea level rise. That included: </p>
<ul>
<li><p>delving into the geological record to study how coastal systems responded to past sea level rise, following the last Ice Age</p></li>
<li><p>tapping into a global network of <a href="https://www.usgs.gov/centers/eesc/science/surface-elevation-table">survey benchmarks</a> in mangroves and tidal marshes</p></li>
<li><p>analysing satellite imagery for changes in the extent of wetlands and coral islands at varying rates of sea level rise.</p></li>
</ul>
<p>Altogether, our international team assessed 190 mangroves, 477 tidal marshes and 872 coral reef islands around the world. </p>
<p>We then used computer modelling to work out how much these coastal ecosystems would be exposed to rapid sea level rise under projected warming scenarios. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/545438/original/file-20230830-15-1g4pn5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo of the eroding wetland at Towra Point in Sydney, showing the stumps and exposed roots of trees washed up on the beach" src="https://images.theconversation.com/files/545438/original/file-20230830-15-1g4pn5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/545438/original/file-20230830-15-1g4pn5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/545438/original/file-20230830-15-1g4pn5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/545438/original/file-20230830-15-1g4pn5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/545438/original/file-20230830-15-1g4pn5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/545438/original/file-20230830-15-1g4pn5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/545438/original/file-20230830-15-1g4pn5.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">Eroding wetland at Towra Point in Sydney.</span>
<span class="attribution"><span class="source">Neil Saintilan</span></span>
</figcaption>
</figure>
<h2>What we found</h2>
<p>Mangroves, tidal marshes and coral islands can cope with low rates of sea-level rise. They remain stable and healthy. </p>
<p>We found most tidal marshes and mangroves are keeping pace with current rates of sea level rise, around 2–4mm per year. Coral islands also appear stable under these conditions. </p>
<p>In some locations, land is sinking, so the relative rate of sea level rise is greater. It may be double this 2–4mm figure or more, comparable to rates expected under future climate change. In these situations, we found <a href="https://theconversation.com/not-waving-drowning-why-keeping-warming-under-1-5-is-a-life-or-death-matter-for-tidal-marshes-187540">marshes failing to keep up</a> with sea level rise. They are slowly drowning and in some cases, breaking up. What’s more, these are the same rates of sea level rise under which marshes and mangrove drown in the geological record.</p>
<p>These cases give us a glimpse of the future in a warming world.</p>
<p>So if the rate of sea level rise doubles to 7 or 8 millimetres a year, it becomes “very likely” (90% probability) mangroves and tidal marshes will no longer keep pace, and “likely” (about 67% probability) coral islands will undergo rapid changes. These rates will be reached when the 2.0°C warming threshold is exceeded. </p>
<p>Even at the lower rates of sea level rise we would have between 1.5°C and 2.0°C of warming (4 or 5mm a year), extensive loss of mangrove and tidal marsh is likely. </p>
<p>Tidal marshes are less exposed to these rates of sea level rise than mangroves because they occur in regions where the land is rising, reducing the relative rate of sea level rise.</p>
<iframe title="" aria-label="Table" id="datawrapper-chart-X0tLs" src="https://datawrapper.dwcdn.net/X0tLs/1/" scrolling="no" frameborder="0" style="width: 0; min-width: 100% !important; border: none;" height="340" data-external="1" width="100%"></iframe>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/rising-seas-threaten-to-drown-important-mangrove-forests-unless-we-intervene-49146">Rising seas threaten to drown important mangrove forests, unless we intervene</a>
</strong>
</em>
</p>
<hr>
<h2>Let’s give coastal ecosystems a fighting chance</h2>
<p>We know mangroves and tidal marshes have survived rapid sea level rise before, at rates even higher than those projected under extreme climate change. </p>
<p>They won’t have long enough to build up root systems or trap sediment in order to stay in place, so they will seek higher ground by shifting landward into newly flooded coastal lowlands. </p>
<p>But this time, they will be competing with other land uses and increasingly trapped behind coastal levees and hard barriers such as roads and buildings. </p>
<p>If the global temperature rise is limited to 2°C, coastal ecosystems have a fighting chance. But if this threshold is exceeded, they will need more help. </p>
<p>Intervention is needed to enable the retreat of mangroves and tidal marshes across our coastal landscapes. There is a role for governments in designating retreat pathways, controlling coastal development, and expanding coastal nature reserves into higher ground. </p>
<p>The future of the world’s living coastlines is in our hands. If we work to restore mangroves and tidal marshes to their former extent, they can help us tackle climate change. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/climate-change-can-drive-social-tipping-points-for-better-or-for-worse-210641">Climate change can drive social tipping points – for better or for worse</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/211431/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Neil Saintilan receives funding from the Australian Research Council, the National Environmental Science Program, and the Alexander Von Humboldt Foundation.</span></em></p>Rising seas are pushing coastal ecosystems to the limit of endurance. Now international research reveals a “tipping point” will be reached if we allow more than 2 degrees of global warming.Neil Saintilan, Professor, School of Natural Sciences, Macquarie UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2120492023-08-24T14:55:46Z2023-08-24T14:55:46ZHow do coral reefs thrive in parts of the ocean that are low in nutrients? By eating their algal companions<figure><img src="https://images.theconversation.com/files/544330/original/file-20230823-36239-dk7lmg.jpg?ixlib=rb-1.1.0&rect=31%2C25%2C4233%2C3088&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Coral reefs are hotspots of productivity in otherwise nutrient-poor parts of our oceans.</span> <span class="attribution"><span class="source">Joerg Wiedenmann & Cecilia D'Angelo/University of Southampton</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p>Coral reefs thrive in parts of the world’s oceans that are low in nutrients. This mystery has puzzled scientists for centuries and has become known as the <a href="https://www.nhm.ac.uk/discover/charles-darwin-coral-conundrum.html">“Darwin paradox of coral reefs”</a>.</p>
<p>Our <a href="https://doi.org/10.1038/s41586-023-06442-5">new study</a> adds the missing piece of the puzzle. We found that many species of coral <a href="https://youtu.be/DsQO_1sB5is">cultivate and feed on</a> the microscopic algae that live inside their cells. This vegetarian diet allows the corals to tap into a large pool of nutrients that was previously considered unavailable to them.</p>
<p><a href="https://www.britannica.com/animal/coral">Stony corals</a> are soft-bodied animals made up of many individual polyps that live together as a colony. They secrete limestone skeletons that form the foundation of reefs. The coral polyps acquire nutritious compounds rich in nitrogen and phosphorus by catching prey like <a href="https://www.britannica.com/science/zooplankton">zooplankton</a> with their tentacles. </p>
<p>Many coral animals are also dependent on a symbiosis – a mutually beneficial relationship – with the microscopic algae that live inside their cells. These photosynthetic algae produce large amounts of carbon-rich compounds, such as sugars, and transfer them to the host coral to generate energy. However, as most photosynthetic products are deficient in nitrogen and phosphorous, they cannot sustain the growth of the animals. </p>
<p>Our findings suggest that, while coral animals may survive brief periods of starvation by feeding on their symbionts, some coral reefs could face the risk of prolonged nutrient deficiency due to global warming. This is concerning. Coral reefs are <a href="https://www.unep.org/explore-topics/oceans-seas/what-we-do/protecting-coral-reefs/why-protecting-coral-reefs-matters">important underwater ecosystems</a> that provide a home and feeding ground for countless organisms, sustaining around 25% of the world’s ocean biodiversity.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/544337/original/file-20230823-21-dat40a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Symbiont algae from a reef coral viewed under a microscope." src="https://images.theconversation.com/files/544337/original/file-20230823-21-dat40a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/544337/original/file-20230823-21-dat40a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=535&fit=crop&dpr=1 600w, https://images.theconversation.com/files/544337/original/file-20230823-21-dat40a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=535&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/544337/original/file-20230823-21-dat40a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=535&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/544337/original/file-20230823-21-dat40a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=672&fit=crop&dpr=1 754w, https://images.theconversation.com/files/544337/original/file-20230823-21-dat40a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=672&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/544337/original/file-20230823-21-dat40a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=672&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Symbiont algae from a reef coral viewed under a microscope.</span>
<span class="attribution"><span class="source">J. Wiedenmann & C. D’Angelo/University of Southampton</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Vegetarian diet</h2>
<p>The symbiotic algae living within the corals are very efficient at taking up dissolved inorganic nutrients, like nitrate and phosphate, from the surrounding seawater. Even in nutrient-poor areas of the ocean, these compounds are present in considerable amounts as excretion products of organisms, <a href="https://www.nature.com/articles/35099547">such as sponges</a>, that live close by. Ocean currents can also <a href="https://onlinelibrary.wiley.com/doi/epdf/10.1111/ecog.04097">transport these nutrients</a> to reefs. </p>
<p>The coral host, on the other hand, cannot absorb or use nitrate and phosphate directly. But, through a series of long-term laboratory experiments, we demonstrated that corals actually digest some of their symbiont population to access the nitrogen and phosphorus that these algae absorb from the water. </p>
<p>To provide evidence that the nutrients accumulated by the growing coral tissue originated from the symbionts, we supplied the corals with a chemical form of nitrogen that can only be absorbed from the water by the symbionts, not by the coral host.</p>
<p>This nutrient compound was marked by a technique called <a href="https://www.sciencedirect.com/science/article/pii/S0039914018309226">isotopic labelling</a>, which uses nitrogen atoms that are heavier than normal. These “heavy” isotopes allowed us to track the movement of nitrogen between the partners of the symbiosis by ultrasensitive detection methods. </p>
<p>With this method, we could unambiguously demonstrate that the nitrogen atoms that sustained the growth of the coral tissue were derived from the dissolved inorganic nutrients that were fed to their symbiont algae.</p>
<p>Our data suggest that most species of symbiotic corals can supplement their nutrition through such a vegetarian diet.</p>
<h2>From the laboratory to the ocean</h2>
<p>Together with our <a href="https://doi.org/10.1038/s41586-023-06442-5">colleagues</a>, we also analysed corals growing around remote islands in the Indian Ocean, some with seabirds on them and some without. Our results show that corals have the potential to farm and feed on their symbiont algae in the wild too. </p>
<p>The reefs around some of these islands are supplied with substantial amounts of nutrients that come from “guano” – the excrement of seabirds nesting on the islands. On some of the other islands, seabird colonies <a href="https://www.nature.com/articles/s41586-018-0202-3">have been decimated</a> by invasive rats. The reefs surrounding these islands receive fewer nutrients. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/invasive-rats-are-changing-fish-behaviour-on-coral-reefs-new-study-197215">Invasive rats are changing fish behaviour on coral reefs – new study</a>
</strong>
</em>
</p>
<hr>
<p>We measured the growth of <a href="https://www.nationalgeographic.com/animals/invertebrates/facts/staghorn-coral">staghorn coral</a> colonies both around islands with and without dense seabird populations and found that growth was more than twice as fast on reefs that were supplied with seabird nutrients. About half of the nitrogen molecules in the tissue of the coral animals from islands with seabirds could be traced back to uptake by the symbiont algae.</p>
<figure class="align-center ">
<img alt="A group of seabirds above a tropical beach." src="https://images.theconversation.com/files/544331/original/file-20230823-7859-833k3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/544331/original/file-20230823-7859-833k3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/544331/original/file-20230823-7859-833k3d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/544331/original/file-20230823-7859-833k3d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/544331/original/file-20230823-7859-833k3d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/544331/original/file-20230823-7859-833k3d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/544331/original/file-20230823-7859-833k3d.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">Reefs around islands in the Indian Ocean receive additional nutrients if the islands are inhabited by seabirds.</span>
<span class="attribution"><span class="source">N. Graham/Lancaster University</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Global warming could complicate matters</h2>
<p>In the future, some coral reefs could face a <a href="https://www.nature.com/articles/ncomms10581">decrease in nutrient availability</a> due to global warming. Research suggests that warming surface waters are <a href="https://www.nature.com/articles/nature05317">less likely to</a> receive nutrients from deeper water layers. The reduced water productivity could result in fewer nutrients for their symbionts and subsequently less food for the coral animals. </p>
<p>Our study indicates that some coral reefs might become vulnerable to starvation as ocean temperatures warm. When we moved corals from water with ample nutrients to water with fewer nutrients, they continued to eat their symbiont algae. This behaviour allowed them to sustain their growth for a few weeks, even in the absence of feeding.</p>
<p>But once they had exhausted their population of symbiotic algae, the coral underwent bleaching (referring to the white appearance of the corals with low symbiont numbers in their tissue), stopped growing – and in some cases eventually died.</p>
<figure class="align-center ">
<img alt="Two photos comparing coral growth in different environments." src="https://images.theconversation.com/files/544334/original/file-20230823-15-yzs1p7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/544334/original/file-20230823-15-yzs1p7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=526&fit=crop&dpr=1 600w, https://images.theconversation.com/files/544334/original/file-20230823-15-yzs1p7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=526&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/544334/original/file-20230823-15-yzs1p7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=526&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/544334/original/file-20230823-15-yzs1p7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=661&fit=crop&dpr=1 754w, https://images.theconversation.com/files/544334/original/file-20230823-15-yzs1p7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=661&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/544334/original/file-20230823-15-yzs1p7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=661&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Corals grew fast in nutrient-rich water despite the absence of food (top). Corals in nutrient-depleted water stopped growing and showed a bleached appearance (bottom).</span>
<span class="attribution"><span class="source">L. Mardones-Velozo, C. D’Angelo & J. Wiedenmann, University of Southampton</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>Our findings reveal that corals can not only acquire nitrogen and phosphorus by feeding on prey as other animals do. But, by eating parts of their symbiont stock, they can also efficiently tap into the pool of dissolved inorganic nitrogen and phosphorus that is otherwise only accessible to plants.</p>
<p>Through this process, symbiotic corals gain an advantage over other animals in environments that are low in nutrients, explaining their prominent role in the formation of reefs in nutrient-poor water. </p>
<p>However, increasingly severe nutrient depletion will add a further threat to some coral reefs already experiencing bleaching caused by heat stress.</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>
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<p><strong><em>Don’t have time to read about climate change as much as you’d like?</em></strong>
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<hr><img src="https://counter.theconversation.com/content/212049/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jörg Wiedenmann receives funding from Natural Environment Research Council (NERC) (NE/T001364/1).
Paul Wilson and Peter Franklin (University of Southampton) and Nick Graham (Lancaster University) contributed to the press release that fomed the basis of this article.</span></em></p><p class="fine-print"><em><span>Cecilia D'Angelo receives funding from Natural Environment Research Council NERC (NE/T001364/1). </span></em></p>Reef corals grow vigorously in nutrient poor water – new research has found out why.Jörg Wiedenmann, Professor of Biological Oceanography & Head of the Coral Reef Laboratory, University of SouthamptonCecilia D'Angelo, Associate Professor, Coral Reef Laboratory, University of SouthamptonLicensed 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>
<figure class="align-center ">
<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">
<figcaption>
<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>
</figcaption>
</figure>
<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>
<hr>
<p>
<em>
<strong>
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>
</figcaption>
</figure>
<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>
<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>
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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>
</figcaption>
</figure>
<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>
<hr>
<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>
</strong>
</em>
</p>
<hr>
<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>
<figure class="align-center zoomable">
<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>
<figcaption>
<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>
</figcaption>
</figure>
<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>
<figure class="align-center zoomable">
<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>
</figcaption>
</figure>
<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>
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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/2105582023-08-09T02:21:15Z2023-08-09T02:21:15ZIs the Great Barrier Reef reviving – or dying? Here’s what’s happening beyond the headlines<p>The Great Barrier Reef is not dead. Nor is it in good health. The truth is complex. To understand what’s going on takes more than a headline. </p>
<p>For the last 37 years, our organisation has monitored the health of the world’s largest reef. Each year, we add our findings to our dataset, the Reef’s longest running and largest coverage. This lets us produce annual updates for the northern, central and southern regions of the Reef. That makes us perhaps the team best qualified to answer the question many people have – how is the Reef going? </p>
<p>Released today, this <a href="https://www.aims.gov.au/monitoring-great-barrier-reef/gbr-condition-summary-2022-23">year’s update</a> paints a complex picture. It wasn’t long ago the Great Barrier Reef was reeling from successive disturbances, ranging from marine heatwaves and coral bleaching to crown-of-thorns starfish outbreaks and cyclone damage, with widespread death of many corals especially during the heatwaves of 2016 and 2017.</p>
<p>Since then, the Reef has rebounded. Generally cooler La Niña conditions mean hard corals have recovered significant ground, regrowing from very low levels after a decade of cumulative disturbances to record high levels in 2022 across two-thirds of the reef. </p>
<p>The Reef has shown an impressive ability to recover from widespread disturbances, when it gets a chance – it’s not all just bleaching and death. But it’s also true we’re heading towards a future where hotter water temperatures will <a href="https://www.nature.com/articles/srep39666">likely cause bleaching</a> every year, along with ongoing threats of cyclones and coral-eating starfish. Recovery requires reprieve – and those opportunities will diminish as climate change progresses.</p>
<p>Last year, for instance, parts of the Reef <a href="https://www.abc.net.au/news/2023-08-09/mass-coral-bleaching-halts-great-barrier-reef-recovery/102706194">experienced bleaching</a> in the middle of La Niña – the first time that’s happened on record. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/541837/original/file-20230809-17-7xg9in.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="barrier reef coral trends 2023" src="https://images.theconversation.com/files/541837/original/file-20230809-17-7xg9in.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541837/original/file-20230809-17-7xg9in.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=140&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541837/original/file-20230809-17-7xg9in.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=140&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541837/original/file-20230809-17-7xg9in.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=140&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541837/original/file-20230809-17-7xg9in.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=176&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541837/original/file-20230809-17-7xg9in.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=176&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541837/original/file-20230809-17-7xg9in.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=176&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Trends in hard coral cover across the Great Barrier Reef’s three sections from 1986-2023.</span>
<span class="attribution"><span class="source">AIMS</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>What’s happening on the Reef?</h2>
<p>To take the pulse of the Great Barrier Reef, one indicator we use is hard coral cover. It’s a widely used, robust indicator of reef health, but it doesn’t tell the whole story. We also collect detailed data on coral and fish populations, diversity, structural complexity, and abundance of juvenile corals. And we take digital photographs and convert them into 3D photogrammetry models so we can analyse what’s happening in more depth than ever before.</p>
<p>Here’s what our analysis shows. </p>
<p>Over the last few years, the Reef was mostly in La Niña conditions. That gave the hard-hit northern and central parts of the reef a chance to begin recovery. Many reefs had a high proportion of <em>Acropora</em> corals, of which the best known are the staghorn and plate corals. These species have been a vital part of the reef over 37 years of monitoring – and probably for millennia.</p>
<p>These corals are the most common on many reefs, and grow fast. Because of that, they tend to dominate trends in hard coral cover.</p>
<figure class="align-center ">
<img alt="High cover of Acropora corals on the southern GBR." src="https://images.theconversation.com/files/541826/original/file-20230808-31-49o8nw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541826/original/file-20230808-31-49o8nw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541826/original/file-20230808-31-49o8nw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541826/original/file-20230808-31-49o8nw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541826/original/file-20230808-31-49o8nw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541826/original/file-20230808-31-49o8nw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541826/original/file-20230808-31-49o8nw.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">This reef in the southern section has a high cover of Acropora corals.</span>
<span class="attribution"><span class="source">AIMS, CC BY-ND</span></span>
</figcaption>
</figure> <p></p>
<p>Does this mean the Great Barrier Reef’s recovery in 2022 relied on “weedy” corals which are taking over? Yes and no. The natural ecological niche of <em>Acropora</em> corals has always been to rapidly fill empty space, which means it tends to dominate trends in coral recovery. </p>
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Read more:
<a href="https://theconversation.com/record-coral-cover-doesnt-necessarily-mean-the-great-barrier-reef-is-in-good-health-despite-what-you-may-have-heard-188233">Record coral cover doesn't necessarily mean the Great Barrier Reef is in good health (despite what you may have heard)</a>
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</em>
</p>
<hr>
<p>Again, the story is more complicated than the headlines. Some reefs have recovered strongly, some very little. Some reefs are recovering with less <em>Acropora</em> than before, some with more. Each reef is charting its own course on the journey from impact to recovery and back again. </p>
<p>Overall, the record high hard coral cover seen last year was welcome news, representing recovery across much of the Reef in the absence of common coral killers. </p>
<h2>But what about recent heating?</h2>
<p>This year, the rapid coral rebound paused. Some reefs continued to recover, but these were offset by others which lost coral. Coral loss came from effects of the 2022 bleaching event in northern and central regions, crown-of-thorns starfish predation in the northern and southern regions, damage from Tropical Cyclone Tiffany in the north and coral disease in some areas of the south. </p>
<p>The picture is complex. Recovery here, fresh losses there.</p>
<p>While the recovery we reported last year was welcome news, there are challenges ahead. The spectre of global annual coral bleaching will soon become a reality. </p>
<figure class="align-center ">
<img alt="Bleached corals on the central Great Barrier Reef during the summer of 2022" src="https://images.theconversation.com/files/541819/original/file-20230808-25-fxdksi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541819/original/file-20230808-25-fxdksi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541819/original/file-20230808-25-fxdksi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541819/original/file-20230808-25-fxdksi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541819/original/file-20230808-25-fxdksi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541819/original/file-20230808-25-fxdksi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541819/original/file-20230808-25-fxdksi.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">Coral bleaching on on the central Great Barrier Reef during the summer of 2022.</span>
<span class="attribution"><span class="source">AIMS, CC BY-ND</span></span>
</figcaption>
</figure>
<p>Right now, marine heatwaves are <a href="https://www.washingtonpost.com/weather/2023/06/23/ocean-heatwave-northatlantic-uk-climate/">sweeping through</a> ocean basins in the northern hemisphere. Sea surface temperatures are far above long term averages. </p>
<p>At least eight countries are reporting coral bleaching, including <a href="https://www.theguardian.com/environment/2023/aug/04/florida-coral-bleached-ocean-heat">the United States</a> and Belize. This summer, it looks likely we’ll see our first El Niño on the Great Barrier Reef since 2016, bringing higher sea surface temperatures. That last El Niño – coupled with global heating – was the direct cause of the 2016–17 mass bleaching and mass death of corals.</p>
<p>The prognosis is, in short, extremely concerning. Yes, the Reef has rebounded beyond our expectations. But now the heat is back on. If we get mass bleaching like 2016 – or even worse – it could undo all the recent recovery. </p>
<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>
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</em>
</p>
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</p><img src="https://counter.theconversation.com/content/210558/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mike Emslie works for the Australian Institute of Marine Science which receives funding from the Australian Government to conduct the Long-Term Monitoring Program.
AIMS also receives external funding from a number of sources including but not limited to the Australian Government's Reef Trust Partnership, Woodside Energy, Santos Ltd, BHP, Carnegie Institution for Science, The European Union’s Marie Skłodowska-Curie Actions, Taronga Conservation Society Australia, Taronga Foundation, Smithsonian Conservation Biology Institute, Accenture and the Allen Coral Atlas.
</span></em></p><p class="fine-print"><em><span>Daniela Ceccarelli works for the Australian Institute of Marine Science which receives funding from the Australian Government to conduct the Long-Term Monitoring Program.
</span></em></p><p class="fine-print"><em><span>David Wachenfeld works for the Australian Institute of Marine Science which receives funding from the Australian Government to conduct the Long-Term Monitoring Program. </span></em></p>In recent years, the Barrier Reef has had a reprieve – and coral has regrown strongly. But now the reprieve looks to be over and the heat is back onMike Emslie, Senior Research Scientist, Australian Institute of Marine ScienceDaniela Ceccarelli, Research fellow, Australian Institute of Marine ScienceDavid Wachenfeld, Research Program Director- Reef Ecology and Monitoring, Australian Institute of Marine ScienceLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2110512023-08-07T15:01:24Z2023-08-07T15:01:24ZHow some fish learned to hide behind others to hunt – new research<figure><img src="https://images.theconversation.com/files/541263/original/file-20230804-20-ocohkj.jpg?ixlib=rb-1.1.0&rect=57%2C57%2C6307%2C4179&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/closeup-western-atlantic-trumpetfish-2310048221">Griffin Gillespie/Shutterstock</a></span></figcaption></figure><p>Human hunters once used stalking horses as common practice – a domesticated animal (or a wooden replica), which people guided towards their quarry while crouching behind it. People believed the stalking horse would not spook wildfowl, allowing them to approach their prey within shooting distance without detection. </p>
<p>My team’s <a href="https://doi.org/10.1016/j.cub.2023.05.075">new study</a> found a Caribbean reef fish that adopts the same strategy, providing the first evidence of a predator using another animal for concealment in the wild.</p>
<p>Trumpetfish (<em>Aulostomus maculatus</em>) are predatory fish abundant throughout Caribbean coral reefs. These fish prey on small reef fish and have several different hunting strategies, including hovering upside-down to wait for passing prey. </p>
<p>Divers regularly report seeing trumpetfish <a href="https://zslpublications.onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1980.tb01458.x">swimming closely alongside</a> a larger typically less-threatening fish, such as a parrotfish or surgeonfish , in a behaviour known as shadowing (also riding or aligning).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/541265/original/file-20230804-29-ubxla5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Stoplight parrotfish (Sparisoma viride) underwater in the tropical caribbean sea of Bonaire" src="https://images.theconversation.com/files/541265/original/file-20230804-29-ubxla5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541265/original/file-20230804-29-ubxla5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541265/original/file-20230804-29-ubxla5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541265/original/file-20230804-29-ubxla5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541265/original/file-20230804-29-ubxla5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541265/original/file-20230804-29-ubxla5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541265/original/file-20230804-29-ubxla5.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">A parrotfish – one of the fish trumpetfish like to hide behind.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/stoplight-parrotfish-sparisoma-viride-underwater-tropical-1564175002">aquapix/Shutterstock</a></span>
</figcaption>
</figure>
<p>Much like the stalking horse, people assumed this behaviour allowed trumpetfish to approach closer to their prey unseen, but this hypothesis had never been tested –until now.</p>
<h2>Model behaviour</h2>
<p>While scuba diving on coral reefs off the Dutch Caribbean island of Curaçao, my team of researchers set up a pulley system to reel a set of 3D-printed models of trumpetfish and parrotfish along a nylon line through the water. The models were reeled one-by-one past groups of damselfish (<em>Stegastes partitus</em>), which are a favourite meal for trumpetfish. </p>
<p>Damselfish respond to potential predators by inspecting approaching fish then fleeing towards their shelter if they sense danger. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/km9H4A71ieo?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>So, we filmed and analysed their responses to each model to see if they would detect a hiding trumpetfish. </p>
<p>When a trumpetfish model moved past alone, damselfish swam to inspect the model, then took off back to the safety of their shelter. When a model of an herbivorous parrotfish (<em>Sparisoma viride</em>) swam past by itself, the damselfish gave the model a once over but were far less likely to flee. </p>
<p>However, when we attached a trumpetfish model to the side of a parrotfish model (to replicate the shadowing behaviour of the real trumpetfish) the damselfish reacted almost the same as when it saw a parrotfish model alone: the damselfish did not detect the hidden trumpetfish.</p>
<h2>Why disguise is important</h2>
<p>While many animals use camouflage, even the most well disguised objects become <a href="https://royalsocietypublishing.org/doi/10.1098/rsbl.2008.0758">noticeable when they’re moving</a>. Animals can struggle to balance their need to move with their need to remain concealed and evolution has helped them develop some creative solutions. For example, the <a href="https://www.australiangeographic.com.au/blogs/creatura-blog/2018/07/wrap-around-spider/">wrap-around spider</a>, found in Australia, spins a new web every evening. At dawn it destroys the web and uses its concave belly to flatten itself around the curve of a tree branch and hide from birds during daylight hours. </p>
<p>And two octopus species “walk” on two tentacles to <a href="https://www.nbcnews.com/id/wbna7286853">camouflage themselves as plants</a> so they can hide from predators. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/541244/original/file-20230804-27-fsmt9k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Man crouches behind wooden screen of a horse while he holds a gun" src="https://images.theconversation.com/files/541244/original/file-20230804-27-fsmt9k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/541244/original/file-20230804-27-fsmt9k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=374&fit=crop&dpr=1 600w, https://images.theconversation.com/files/541244/original/file-20230804-27-fsmt9k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=374&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/541244/original/file-20230804-27-fsmt9k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=374&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/541244/original/file-20230804-27-fsmt9k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=470&fit=crop&dpr=1 754w, https://images.theconversation.com/files/541244/original/file-20230804-27-fsmt9k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=470&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/541244/original/file-20230804-27-fsmt9k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=470&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An 1875 image of a human hunter using a stalking horse.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:RO(1875)_P215_APPROACHING_THE_FOWL_WITH_STALKING-HORSE.jpg">British Library</a></span>
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</figure>
<p>There are additional benefits of shadowing behaviour. For example, small trumpetfish may benefit from being less visible to their predators as well as from their prey. Hiding in this way may also reduce the number of aggressive encounters that trumpetfish have with territorial species.</p>
<h2>Climate change shaping behaviour</h2>
<p>Predators often use the physical landscape of a habitat as cover when they hunt their prey, such as hiding among rocky outcrops or vegetation. So the use of other animals may be an important alternative when habitat cover is unavailable. Indeed, in a previous study we found shadowing behaviour <a href="https://link.springer.com/article/10.1007/s00227-022-04057-4#:%7E:text=Discussion,geographically%20clustered%20within%20certain%20areas.">was more common in less complex habitats</a> such as patchy coral reefs. </p>
<p>Coral reefs across the globe are facing increasingly severe challenges, including climate change, pollution and ocean acidification. They are undergoing an alarming rate of degradation, becoming <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0126004#pone.0126004.ref007">patchier, less complex and less biodiverse</a>. Given this trend, we may see an increase in shadowing in the future. </p>
<p>Our study highlights one of the extraordinary strategies predators use to target their prey. Human hunters may have realised that stalking horses could be used to increase their hunting success but it appears fish may have evolved shadowing long before we did.</p><img src="https://counter.theconversation.com/content/211051/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sam Matchette works for the University of Cambridge, UK. This project was funded by the Fisheries Society of the British Isles (FSBI) and the Association for the Study of Animal Behaviour (ASAB). </span></em></p>Trumpetfish are the first known predator to hide behind another animal when hunting.Sam Matchette, Research Associate in Marine Behaviour , University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2107872023-08-01T06:30:55Z2023-08-01T06:30:55ZOut of danger because the UN said so? Hardly – the Barrier Reef is still in hot water<figure><img src="https://images.theconversation.com/files/540330/original/file-20230801-198210-3bop0q.jpg?ixlib=rb-1.1.0&rect=0%2C162%2C5184%2C3282&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>Today is a good day to be Environment Minister Tanya Plibersek. UNESCO, the United Nations body expected to vote on whether to list the Great Barrier Reef as “in danger”, instead <a href="https://whc.unesco.org/archive/2023/whc23-45com-7B.Add-en.pdf#page26">deferred the decision</a> for another year. This, an insider told French newspaper Le Monde, was largely due to the change in approach between the former Coalition government and Labor. </p>
<p>“It’s a bit like night and day,” the insider said – which was promptly included in Plibersek’s <a href="https://minister.dcceew.gov.au/plibersek/media-releases/un-recognises-australian-government-action-protect-great-barrier-reef">media release</a>.</p>
<p>So, it’s a good day for the government. But is it a good day for the reef? No. The longstanding threats to the world’s largest coral ecosystem are still there, from agricultural runoff, to shipping pollution, to fisheries, although we have seen improvement in areas such as <a href="https://reportcard.reefplan.qld.gov.au">water quality</a>.</p>
<p>But any incremental improvement will be for naught if we don’t respond to the big one – climate change – with the necessary urgency. This year has seen <a href="https://www.theguardian.com/environment/2023/jul/05/tuesday-was-worlds-hottest-day-on-record-breaking-mondays-record">record-breaking heat</a> and extreme weather, with <a href="https://www.bbc.com/future/article/20230720-theres-a-heatwave-in-the-sea-and-scientists-are-worried">intense heating</a> of the oceans during the northern summer. These intense marine heatwaves have devastated efforts to <a href="https://www.local10.com/weather/2023/07/28/um-rescuers-are-urgently-trying-to-save-corals-from-what-could-be-devastating-for-oceans/">regrow or protect</a> coral in places like Florida. And our own summer is just around the corner. </p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/seriously-ugly-heres-how-australia-will-look-if-the-world-heats-by-3-c-this-century-157875">Seriously ugly: here's how Australia will look if the world heats by 3°C this century</a>
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<p>It is not hyperbole to say the next two years are likely to be very bad for the Great Barrier Reef. It’s <a href="https://www.theguardian.com/environment/2023/jul/22/marine-heatwave-in-north-east-queensland-sets-off-alarm-over-health-of-great-barrier-reef">already enduring</a> a winter marine heatwave. Background warming primes the reef for mass coral bleaching and death. We’ve already experienced this in 2016-17, which brought <a href="https://link.springer.com/article/10.1007/s00338-018-01749-6">back-to-back</a> global mass coral bleaching and mortality events including on the Great Barrier Reef. We can expect more as global temperatures continue to soar. </p>
<p>While the government may congratulate itself on not being the previous one, it’s nowhere near enough. We’re facing D-Day for the reef, as for many other ecosystems. Incrementalism and politics as usual are simply not going to be enough. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1686102788005408769"}"></div></p>
<h2>What has the government done for the reef to date?</h2>
<p>To its credit, Labor has made some marginal improvements to the Great Barrier Reef’s prospects. The <a href="https://minister.dcceew.gov.au/plibersek/media-releases/un-recognises-australian-government-action-protect-great-barrier-reef">list</a> includes: legislating net zero greenhouse emissions, with a 43% cut within seven years; improving water quality with revegetation projects and work to reduce soil erosion; and <a href="https://www.theguardian.com/environment/2023/jun/05/conservationists-welcome-gillnet-fishing-ban-in-great-barrier-reef-world-heritage-area">ending gillnet use</a> in the Great Barrier Reef Marine Park by 2027.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/warm-is-the-new-norm-for-the-great-barrier-reef-and-a-likely-el-nino-raises-red-flags-206750">Warm is the new norm for the Great Barrier Reef – and a likely El Niño raises red flags</a>
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<p>For at least a century, cattle, sugarcane and other farmers have relied on rivers to take animal waste and fertiliser runoff away from their properties. In much of Queensland, that means the runoff heads for the Great Barrier Reef instead. We did see some improvement under the Coalition government, which put A$443 million into trying to <a href="https://www.abc.net.au/news/2023-04-22/remember-that-record-funding-for-the-great-barrier-reef/102252268">solve the issue</a>. Labor has put in a <a href="https://minister.dcceew.gov.au/plibersek/media-releases/joint-media-release-improving-water-quality-protect-great-barrier-reef">further $150 million</a>. But the water quality problem is still <a href="https://www.reefplan.qld.gov.au/tracking-progress/reef-report-card/2020">not solved</a>. </p>
<p>Ending gillnet use in the marine park is also welcome, given these nets can and do catch and kill sharks, dugongs and turtles. But challenging though these issues are, they pale in comparison to climate change. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/540364/original/file-20230801-25-vs9gal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="barrier reef" src="https://images.theconversation.com/files/540364/original/file-20230801-25-vs9gal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/540364/original/file-20230801-25-vs9gal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/540364/original/file-20230801-25-vs9gal.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/540364/original/file-20230801-25-vs9gal.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/540364/original/file-20230801-25-vs9gal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/540364/original/file-20230801-25-vs9gal.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/540364/original/file-20230801-25-vs9gal.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">Goldilocks zone: coral likes its water warm – but not too warm.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Tinkering while the reef burns</h2>
<p>When coral is exposed to warmer water than it has evolved to tolerate, it turns white (bleaches) – expelling its symbiotic algae. If the water stays too hot for too long, the corals simply die en masse. </p>
<p>You might have seen the <a href="https://www.whoi.edu/oceanus/feature/is-the-great-barrier-reef-making-a-comeback/">positive reports</a> on coral regrowth during the three recent cooler La Niña years and wonder what the issue is. Isn’t the reef resilient? </p>
<p>Yes – to a point. But after that point, the coral communities collapse. The world is having its <a href="https://www.nytimes.com/2023/07/06/climate/climate-change-record-heat.html">hottest days on record</a>. Coupled with a <a href="https://theconversation.com/its-official-australia-is-set-for-a-hot-dry-el-nino-heres-what-that-means-for-our-flammable-continent-209126">likely El Niño</a>, the reef will likely face the hottest waters yet.</p>
<p>That’s because we still haven’t tackled the root cause. Greenhouse gas emissions are <a href="https://www.theguardian.com/environment/2023/jun/08/global-greenhouse-gas-emissions-at-all-time-high-study-finds">still going up</a>. Year on year, we’re trapping more heat, of which 90% goes <a href="https://theconversation.com/two-trillion-tonnes-of-greenhouse-gases-25-billion-nukes-of-heat-are-we-pushing-earth-out-of-the-goldilocks-zone-202619">into the oceans</a>. Antarctic sea ice is <a href="https://www.sciencealert.com/6-4-sigma-event-antarctic-sea-ice-hits-lowest-point-since-official-records-began">not reforming</a> as it should after last summer. Coral restoration efforts in the United States had to <a href="https://www.nytimes.com/2023/07/31/climate/coral-reefs-heat-florida-ocean-temperatures.html">literally pull</a> their baby corals out of the sea to try to keep them alive, as the water was too hot to live in. </p>
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Read more:
<a href="https://theconversation.com/two-trillion-tonnes-of-greenhouse-gases-25-billion-nukes-of-heat-are-we-pushing-earth-out-of-the-goldilocks-zone-202619">Two trillion tonnes of greenhouse gases, 25 billion nukes of heat: are we pushing Earth out of the Goldilocks zone?</a>
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<p>The North Atlantic Ocean is <a href="https://www.washingtonpost.com/weather/2023/07/28/ocean-temperature-maps-heat-records/">far warmer</a> than it should be, amid a record-breaking northern summer. After the equinox next month, it will be our turn to face the summer sun once more. </p>
<p>Is the Great Barrier Reef in danger? Of course it is. We should not pretend things are normal and can be handled routinely. This year, we’re beginning to see the full force of what the climate crisis will bring. We have clearly underestimated the climate’s sensitivity to rising carbon dioxide levels, and the <a href="https://www.publish.csiro.au/MF/MF99078">gloomy predictions</a> I made more than 20 years ago are looking positively optimistic. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1686120431298961409"}"></div></p>
<p>And still we fail to face up to the fact that the Great Barrier Reef is dying. We thought we might have had decades but it may be just years. Before 1980, no mass bleaching had <a href="https://www.publish.csiro.au/MF/MF99078">ever been recorded</a>. Since then it has only become more common. </p>
<p>Incremental efforts to save the reef, such as looking for <a href="https://www.smithsonianmag.com/science-nature/at-least-one-species-of-pacific-coral-may-thrive-in-warmer-waters-180982561/">heat-tolerant “supercorals”</a>, or replanting baby coral, now look unlikely to work. We don’t have decades or the capacity to find and cultivate resilient corals at scale. And we certainly do not have the <a href="https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/15-1077">massive funding required</a> to replant even a small coral reef. </p>
<p>For people like us who work in the field, it is a devastating time. I now know the feeling of having a broken heart. The pace and intensity of climate change risks rendering all our efforts over the years null and void. It’s almost impossible to look directly at what this will mean for this immense living assemblage, which first began growing more than 600,000 years ago along the Australian east coast. </p>
<p>Giving the government more time to show the reef is improving seems like a fool’s errand. Time is precisely what we don’t have. </p>
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Read more:
<a href="https://theconversation.com/corals-are-starting-to-bleach-as-global-ocean-temperatures-hit-record-highs-209770">Corals are starting to bleach as global ocean temperatures hit record highs</a>
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<img src="https://counter.theconversation.com/content/210787/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ove Hoegh-Guldberg is affiliated with the Great Barrier Reef Foundation and the ARC Centre for Excellence for Coral Reef Studies.
</span></em></p>Incrementalism and politics as usual cannot save the Barrier Reef from the largest threat it faces – the heat ramping up from climate changeOve Hoegh-Guldberg, Professor, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2103722023-07-27T01:28:14Z2023-07-27T01:28:14ZThrough the magnifying glass: how cutting-edge technology is helping scientists understand baby corals<p>New photographic technology has allowed scientists to dive beneath the ocean’s surface and peer into the hidden world of baby corals, to learn how these tiny organisms survive and grow in their crucial first year of life.</p>
<p>In a study <a href="https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/2041-210X.14175">just published</a>, researchers from Southern Cross University and CSIRO describe how advanced imaging techniques offer new ways to monitor baby corals. </p>
<p>Corals provide vital habitat for a large variety of marine life. So it’s useful to better understand how baby corals select and attach to reefs, establish themselves and grow into adult corals.</p>
<p>This knowledge is particularly important if we want to help reefs recover from devastating events such as mass bleaching and cyclones.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/539177/original/file-20230725-23-wrtgjj.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/539177/original/file-20230725-23-wrtgjj.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=439&fit=crop&dpr=1 600w, https://images.theconversation.com/files/539177/original/file-20230725-23-wrtgjj.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=439&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/539177/original/file-20230725-23-wrtgjj.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=439&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/539177/original/file-20230725-23-wrtgjj.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=552&fit=crop&dpr=1 754w, https://images.theconversation.com/files/539177/original/file-20230725-23-wrtgjj.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=552&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/539177/original/file-20230725-23-wrtgjj.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=552&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">3D animation of a 6-month old coral recruit approximately 2.1 mm in size.</span>
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<h2>The secret life of corals</h2>
<p>The life of a coral begins in an annual, synchronised spawning event. Coral colonies release millions of tiny eggs and sperm into the water at the same time. They all rise to the surface where the eggs are fertilised, developing into embryos and then later, into larvae.</p>
<p>Over days or weeks, the millions of larvae disperse with ocean currents. If things go according to nature’s plan, the larvae eventually fall through the water, attach to a reef and grow into adult corals. This process is known as coral “recruitment”.</p>
<p>In healthy coral reefs, this recruitment occurs naturally. But as coral reefs become more degraded – such as through coral bleaching brought on by climate change – <a href="https://www.nature.com/articles/s41586-019-1081-y">fewer coral larvae are produced</a>. This often means recruitment slows down or stops, and natural recovery weakens.</p>
<p>Scientists are working on ways to ensure coral larvae attach to and grow on reefs. This includes collecting coral spawn from the ocean, rearing embryos in floating nurseries and <a href="https://www.nature.com/articles/s41598-017-14546-y">releasing larvae onto damaged reefs</a>.</p>
<p>Coral larvae are less than one millimetre in size, so recruitment occurs on a tiny scale, invisible to the human eye. To better understand the process, researchers traditionally <a href="https://doi.org/10.1007/s003380000081">attach artificial plates</a> to the reef. Once corals have established themselves, the plates are taken back to the lab to be inspected under a microscope.</p>
<p>This method can provide valuable insights, but it does not replicate the natural reef environment. That’s where our research comes in. Essentially, we brought the lab to the reef.</p>
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Read more:
<a href="https://theconversation.com/safe-havens-for-coral-reefs-will-be-almost-non-existent-at-1-5-c-of-global-warming-new-study-176084">Safe havens for coral reefs will be almost non-existent at 1.5°C of global warming – new study</a>
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<img alt="bleached coral reef" src="https://images.theconversation.com/files/539452/original/file-20230726-23-png2p0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/539452/original/file-20230726-23-png2p0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/539452/original/file-20230726-23-png2p0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/539452/original/file-20230726-23-png2p0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/539452/original/file-20230726-23-png2p0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/539452/original/file-20230726-23-png2p0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/539452/original/file-20230726-23-png2p0.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">
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<span class="caption">Mass bleaching and other damaging events is limiting the establishment of baby corals.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
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<h2>Capturing the reef in incredible 3D detail</h2>
<p>Our new study explores the development and application of an innovative imaging approach known as underwater “macrophotogrammetry”.</p>
<p>The technology combines <a href="https://www.uwphotographyguide.com/macro-underwater-photography">macrophotography</a> – photographing small objects close-up, at very high resolution – and <a href="https://www.sciencedirect.com/science/article/pii/S0169534721001944?via%3Dihub">photogrammetry</a> – taking measurements from photos. In this case, we used photogrammetry to “stitch” photos together to recreate three-dimensional models, such as the one below.</p>
<p>The three round objects in the model are “targets” we placed to help the software stitch the photos together. Look closely, and you’ll see a nail head to the left of each target. To give you an idea of the scale of the model, the nail head is 2.8mm in diameter.</p>
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<img alt="" src="https://images.theconversation.com/files/539176/original/file-20230725-25-r3sdrj.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/539176/original/file-20230725-25-r3sdrj.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/539176/original/file-20230725-25-r3sdrj.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/539176/original/file-20230725-25-r3sdrj.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/539176/original/file-20230725-25-r3sdrj.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/539176/original/file-20230725-25-r3sdrj.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/539176/original/file-20230725-25-r3sdrj.gif?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">
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<span class="caption">A 3D animation of approximately 400 cm² of the reef at micrometre resolution.</span>
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<p>Reef-scale photogrammetry can be a <a href="https://doi.org/10.1016/j.tree.2021.07.004">valuable tool</a> to track changes in coral cover and growth over time. However, it does not provide the detailed resolution needed to identify and observe tiny new corals. </p>
<p>Macrophotography provides this incredibly detailed scale. The coupling of the technologies also enables a comprehensive understanding of the entire ecosystem, from the smallest processes to the largest.</p>
<p>We conducted macrophotogrammetry surveys near Lizard Island on the Great Barrier Reef. We marked several 25cm x 25cm locations on the reef. We then captured hundreds of photographs taken at different angles using high-resolution cameras. </p>
<p>Photogrammetry software was used to process the photos, creating precise 3D models that represent the small sections of reef at very high resolution.</p>
<p>The models were examined to find where baby corals settle, to mark their location and measure their size. They reveal the complexity in the reef micro-structure, including tiny crevices, where coral larvae <a href="https://esajournals.onlinelibrary.wiley.com/doi/10.1890/15-0668.1">often settle</a>. </p>
<p>The models also reveal diverse micro-organisms such as small turf algae or invertebrates, <a href="https://www.nature.com/articles/s41598-020-59111-2">which interact with corals</a> during the recruitment process.</p>
<p>Macrophotogrammetry surveys can be conducted at the same reef locations over time. This allows us to monitor the survival and growth of baby corals, and observe changes in the organisms living near them. </p>
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Read more:
<a href="https://theconversation.com/record-coral-cover-doesnt-necessarily-mean-the-great-barrier-reef-is-in-good-health-despite-what-you-may-have-heard-188233">Record coral cover doesn't necessarily mean the Great Barrier Reef is in good health (despite what you may have heard)</a>
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<img alt="two divers in shallow water" src="https://images.theconversation.com/files/539170/original/file-20230725-27-j2f1td.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/539170/original/file-20230725-27-j2f1td.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/539170/original/file-20230725-27-j2f1td.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/539170/original/file-20230725-27-j2f1td.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/539170/original/file-20230725-27-j2f1td.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/539170/original/file-20230725-27-j2f1td.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/539170/original/file-20230725-27-j2f1td.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">
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<span class="caption">The researchers monitor coral recruitment on a reef slope at Lizard Island.</span>
<span class="attribution"><span class="source">Lauren Hardiman CSIRO</span></span>
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<h2>Looking ahead</h2>
<p>Complementary techniques may increase the potential of macrophotogrammetry even further. For example, coral larvae can be <a href="https://doi.org/10.1371/journal.pbio.3001907">dyed various colours</a> before release, making them more visible when they swim to and settle on the reef. This could be captured in 3D models to allow even better tracking of larval restoration efforts.</p>
<p>The use of macrophotogrammetry will deepen our understandings of why some larvae settle and survive on reefs, and others do not. This knowledge can help support our efforts to improve the overall conservation and recovery of coral reefs. </p>
<p>Its application need not be limited to coral reef ecosystems. We are excited about the potential of the technology to drive marine research more broadly.</p>
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Read more:
<a href="https://theconversation.com/thousands-of-photos-captured-by-everyday-australians-reveal-the-secrets-of-our-marine-life-as-oceans-warm-189231">Thousands of photos captured by everyday Australians reveal the secrets of our marine life as oceans warm</a>
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<img src="https://counter.theconversation.com/content/210372/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Marine Gouezo works as a Postdoctoral researcher at Southern Cross University and CSIRO and is involved with the Moving Corals subprogram of the Reef Restoration and Adaptation Program, funded by the partnership between the Australian Government's Reef Trust and the Great Barrier Reef Foundation</span></em></p><p class="fine-print"><em><span>Christopher Doropoulos is a Research Scientist at CSIRO. He co-leads the Moving Corals and EcoRRAP Subprograms as part of the Reef Restoration and Adaptation Program (RRAP). RRAP is funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation.</span></em></p>This knowledge is particularly important if we want to help reefs recover devastating events such as mass bleaching and cyclones.Marine Gouezo, Postdoctoral research fellow, Southern Cross UniversityChristopher Doropoulos, Senior research scientist, CSIROLicensed as Creative Commons – attribution, no derivatives.