tag:theconversation.com,2011:/institutions/national-oceanic-and-atmospheric-administration-1975/articlesNational Oceanic and Atmospheric Administration2024-01-18T13:28:52Ztag: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/2146882023-12-19T18:13:36Z2023-12-19T18:13:36ZShipwrecks teem with underwater life, from microbes to sharks<figure><img src="https://images.theconversation.com/files/555600/original/file-20231024-25-xo8h4f.jpg?ixlib=rb-1.1.0&rect=30%2C15%2C5061%2C3534&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A school of grunts on a sunken World War II German submarine in the Atlantic Ocean off North Carolina.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/diver-and-schooling-tomtates-on-wwii-u-352-german-royalty-free-image/153943111">Karen Doody/Stocktrek Images via Getty Images</a></span></figcaption></figure><p>Humans have sailed the world’s oceans for thousands of years, but they haven’t all reached port. Researchers estimate that there are <a href="https://unesdoc.unesco.org/ark:/48223/pf0000152883">some three million shipwrecks</a> worldwide, resting in shallow rivers and bays, coastal waters and the deep ocean. Many sank during catastrophes – some during storms or after running aground, others in battle or collisions with other vessels.</p>
<p>Shipwrecks like <a href="https://www.britannica.com/topic/Titanic">the RMS Titanic</a>, <a href="https://www.britannica.com/topic/Lusitania-British-ship">RMS Lusitania</a> and <a href="https://www.britannica.com/technology/monitor-ship-type#ref51448">USS Monitor</a> conjure tales of human courage and sacrifice, sunken treasure and unsolved mysteries. But there’s another angle to their stories that doesn’t feature humans. </p>
<p>I have <a href="https://scholar.google.com/citations?user=wZ-kv2AAAAAJ&hl=en">studied the biology of shipwrecks</a> in the United States and internationally for 14 years. From this work, I have learned that shipwrecks are not only cultural icons but can also be biological treasures that create habitat for diverse communities of underwater life. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/FTYyzAxt3JI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The USS Monitor, which sank off Cape Hatteras, North Carolina, in a storm on Dec. 31, 1862, is now a center for sea life.</span></figcaption>
</figure>
<p>Recently, I led an international team of biologists and archaeologists in disentangling the mysteries of how this transformation happens. Drawing on scientific advances from our team and international colleagues, our <a href="https://academic.oup.com/bioscience/article-lookup/doi/10.1093/biosci/biad084">new study</a> describes how wrecked vessels can have second lives as seabed habitats.</p>
<h2>A new home for underwater life</h2>
<p>Ships are typically made of metal or wood. When a vessel sinks, it adds foreign, artificial structure to the seafloor. </p>
<p>For example, the World War II tanker <a href="https://monitor.noaa.gov/shipwrecks/clark.html">E.M. Clark</a> sank on a relatively flat, sandy seabed in 1942 when it was torpedoed by a German submarine. To this day, the intact metal wreck looms over the North Carolina seafloor like an underwater skyscraper, creating an island oasis in the sand. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Bx_uzNvNU1s?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">In this video narrated by NOAA research scientist Avery Paxton, sand tiger sharks hover above the wreck of the E.M. Clark off North Carolina, with vermilion snapper schooling nearby. Jacks and an invasive lionfish also appear.</span></figcaption>
</figure>
<p>The creatures that reside on and around sunken ships are so diverse and abundant that scientists often colloquially call these sites “<a href="https://3d-shipwreck-data-viewer-noaa.hub.arcgis.com/">living shipwrecks</a>.” Marine life ranging from microscopic critters to some of the largest animals in the sea use shipwrecks as homes. Brilliantly colored corals and sponges blanket the wrecks’ surfaces. Silvery schools of baitfish dart and shimmer around the structures, chased by sleek, fast-moving predators. Sharks sometimes cruise around wrecks, likely resting or looking for prey. </p>
<h2>The origin of a second life</h2>
<p>A ship’s transformation from an in-service vessel into a thriving metropolis for marine life can seem like a fairy tale. It has a once-upon-a-time origin story – the wrecking event – and a sequence of life arriving on the sunken structure and beginning to blossom.</p>
<p>Tiny microbes invisible to the naked human eye initially settle on the wreck’s surface, forming a carpet of cells, called a <a href="https://www.britannica.com/science/biofilm">biofilm</a>. This coating helps to <a href="https://doi.org/10.3389/fmars.2019.00048">make the wreck structure suitable</a> for larval animals like sponges and corals to settle and grow there.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Shellfish, deepwater coral and anemones cling to the surface of a sunken wreck." src="https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/555611/original/file-20231024-23-oqeoj2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Diverse sea creatures living on the 19th-century, wooden-hulled Ewing Bank wreck, which lies 2,000 feet (610 meters) deep in the Gulf of Mexico.</span>
<span class="attribution"><a class="source" href="https://oceanexplorer.noaa.gov/explorations/19microbial-stowaways/background/archaeology/media/img2-hires.jpg">NOAA</a></span>
</figcaption>
</figure>
<p>Larger animals like fish sometimes appear within minutes after a ship sinks. <a href="https://coastalscience.noaa.gov/news/artificial-reefs-may-help-tropical-fish-expand-geographic-range-video/">Small fish</a> hide in the structure’s cracks and crevices, while <a href="https://doi.org/10.1016/j.fooweb.2020.e00147">large sharks</a> glide around it. <a href="https://doi.org/10.1016/j.marenvres.2020.104916">Sea turtles</a> and marine mammals such as <a href="https://doi.org/10.1371/journal.pone.0130581">fur seals</a> have also been spotted on wrecks.</p>
<h2>Hot spots for biodiversity</h2>
<p>Shipwrecks host quantities and varieties of marine life that can make them hot spots for biodiversity. The microbes that transform the wreck structure into habitat also enrich the surrounding sand. Evidence from deep Gulf of Mexico wrecks shows that a <a href="https://doi.org/10.1038/s41396-021-00978-y">halo of increased microbial diversity</a> radiates outward anywhere from 650 to 1,000 feet (200-300 meters) from the wreck. In the Atlantic Ocean, <a href="https://doi.org/10.1111/faf.12548">thousands of grouper</a>, a type of reef fish highly valued by fishers, congregate around and inside shipwrecks.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Fish hover above a wrecked ship's surface." src="https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/555613/original/file-20231024-29-aaqe3w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Groupers and a conger eel, bottom center, on the wreck of the German submarine U-576 off the coast of North Carolina.</span>
<span class="attribution"><a class="source" href="https://oceanexplorer.noaa.gov/explorations/16battlefield/logs/sept7/sept7.html">NOAA</a></span>
</figcaption>
</figure>
<p>Shipwrecks can also serve as stepping stones across the ocean floor that animals use as temporary homes while moving from one location to another. This has been documented in areas of the world with dense concentrations of shipwrecks, such as off North Carolina, where storms and war have sunk hundreds of ships.</p>
<p>In this part of the ocean, popularly known as the “<a href="https://www.ncpedia.org/graveyard-atlantic">Graveyard of the Atlantic</a>,” reef fish likely <a href="https://doi.org/10.1038/s42003-019-0398-2">use the islandlike shipwrecks as corridors</a> when moving north or south away from the equator to find favorable water temperatures as climate change <a href="https://theconversation.com/ocean-heat-is-at-record-levels-with-major-consequences-174760">warms the oceans</a>. Scientists have also observed <a href="https://doi.org/10.1002/ecy.2687">sand tiger sharks</a> traveling from one wreck to another, possibly using the shipwrecks like rest stops during migration.</p>
<p>In the deep sea, life growing on shipwrecks can even generate energy. Tube worms that grow on organic shipwreck materials such as paper, cotton and wood host symbiotic bacteria that produce chemical energy. Such tube worm colonies have been documented in the Gulf of Mexico on the steel <a href="https://www.boem.gov/sites/default/files/boem-newsroom/Library/Ocean-Science/Ocean-Science-Jul-Aug-Sep-2014.pdf">luxury yacht Anona</a>. </p>
<h2>Biological mysteries abound</h2>
<p>Despite their biological value, shipwrecks can also threaten underwater life by altering or destroying natural habitats, causing pollution and spreading invasive species.</p>
<p>When a ship sinks, it can damage existing seafloor habitats. In a well-documented case in the Line Islands of the central Pacific, an <a href="https://doi.org/10.1038/ismej.2011.114">iron shipwreck</a> sank on a healthy coral reef. The iron infusion substantially decreased coral cover, and the reef was overcome by algae.</p>
<p>Ships may carry pollutants as fuel or cargo. As shipwrecks deteriorate in seawater, there is a risk that these pollutants may be released. The <a href="https://doi.org/10.1016/j.marpolbul.2021.112087">level of risk</a> depends on how much of the pollutant the ship was carrying and how intact the wreck is. One recent investigation revealed that effects from shipwreck pollutants can be detected in microbes up to <a href="https://doi.org/10.3389/fmars.2022.1017136">80 years after the wreck</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/JTq4b9c3Z00?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Ships and planes wrecked in wartime can leak toxic materials for decades after they come to rest in the ocean.</span></figcaption>
</figure>
<p>Shipwrecks may also inadvertently assist the spread of invasive plants and animals that wreak biological havoc. Wrecks are new structures that invasive species can settle on, grow and use as a hub to expand to other habitats. <a href="https://doi.org/10.1016/j.marpolbul.2020.111394">Invasive cup coral</a> has spread on World War II shipwrecks off Brazil. In Palmyra Atoll in the Pacific, a type of anemone called a corallimorph <a href="https://doi.org/10.1371/journal.pone.0002989">rapidly invaded</a> a shipwreck and now <a href="https://doi.org/10.1007/s10530-018-1696-1">threatens healthy coral reefs</a>.</p>
<h2>The future of shipwreck exploration</h2>
<p>Shipwrecks create millions of study sites that scientists can use to ask questions about marine life and habitats. One of the greatest challenges is that many wrecks are undiscovered or in remote locations. Advances in technology can help researchers see into the most inaccessible areas of the ocean, not only to find shipwrecks but to better understand their biology. </p>
<p>Maximizing discovery will require biologists, archaeologists and engineers to work together to explore these special habitats. Ultimately, the more we learn, the more effectively we can conserve these historical and biological gems.</p><img src="https://counter.theconversation.com/content/214688/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Avery Paxton is affiliated with NOAA National Centers for Coastal Ocean Science. </span></em></p>When ships sink, they add artificial structures to the seafloor that can quickly become diverse, ecologically important underwater communities.Avery Paxton, Research Marine Biologist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2097702023-07-14T12:49:06Z2023-07-14T12:49:06ZCorals are starting to bleach as global ocean temperatures hit record highs<figure><img src="https://images.theconversation.com/files/537483/original/file-20230714-23-yzqhp8.png?ixlib=rb-1.1.0&rect=0%2C23%2C5176%2C3422&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Mass coral bleaching in 2014 left the Coral Reef Monitoring Program monitoring site at Cheeca Rocks off the Florida Keys a blanket of white.</span> <span class="attribution"><a class="source" href="https://www.aoml.noaa.gov/coral-bleaching-cheeca-rocks/">NOAA</a></span></figcaption></figure><p>The water off South Florida is <a href="https://coralreefwatch.noaa.gov/data/vs/ts_figures/ts_multi_year/vs_ts_multiyr_florida_keys.png">over 90 degrees Fahrenheit</a> (32 Celsius) in mid-July, and scientists are already seeing signs of coral bleaching off Central and South America. Particularly concerning is how early in the summer we are seeing these high ocean temperatures. If the <a href="https://theconversation.com/ocean-heat-is-off-the-charts-heres-what-that-means-for-humans-and-ecosystems-around-the-world-207902">extreme heat</a> persists, it could have dire consequences for coral reefs.</p>
<p>Just like humans, corals can handle some degree of stress, but the longer it lasts, the more harm it can do. Corals can’t move to cooler areas when water temperatures rise to dangerous levels. They are stuck in it. For those that are <a href="https://doi.org/10.1007/s00338-022-02232-z">particularly sensitive to temperature stress</a>, that can be devastating.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two photos shows a coral on two different dates, one healthy and reddish in color, the other white." src="https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=246&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=246&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=246&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=310&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=310&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537405/original/file-20230713-21-o01eyh.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=310&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A transplanted coral in the Port of Miami that was healthy in early 2023 had bleached in the warm water by July 11, 2023.</span>
<span class="attribution"><span class="source">NOAA/University of Miami</span></span>
</figcaption>
</figure>
<p><a href="https://scholar.google.com/citations?user=WS4sEzgAAAAJ&hl=en">I lead</a> the <a href="https://www.aoml.noaa.gov/coral-reef-ecosystems/">Coral Program</a> at the National Oceanic and Atmospheric Administration’s Atlantic Oceanographic and Meteorological Lab in Miami, Florida. Healthy coral reef ecosystems are important for humans in numerous ways. Unfortunately, <a href="https://theconversation.com/el-nino-is-coming-and-ocean-temps-are-already-at-record-highs-that-can-spell-disaster-for-fish-and-corals-202424">marine heat waves are becoming more common</a> and more extreme, with potentially devastating consequences for reefs around the world that are already in a fragile state.</p>
<h2>Why coral reefs matter to everyone</h2>
<p>Coral reefs are hot spots of biodiversity. They are often referred to as the <a href="https://oceanexplorer.noaa.gov/okeanos/explorations/10index/background/biodiversity/biodiversity.html">rainforests of the sea</a> because they are home to the highest concentrations of species in the ocean.</p>
<p>Healthy reefs are vibrant ecosystems that support fish and fisheries, which in turn <a href="https://www.noaa.gov/education/resource-collections/marine-life/coral-reef-ecosystems#">support economies and food for millions of people</a>. Additionally, they provide billions of dollars in economic activity every year through tourism, particularly in places like the Florida Keys, where people go to scuba dive, snorkel, fish and experience the natural beauty of coral reefs.</p>
<p>If that isn’t enough, <a href="https://www.usgs.gov/centers/pcmsc/science/role-reefs-coastal-protection">reefs also protect shorelines</a>, beaches and billions of dollars in coastal infrastructure by buffering wave energy, particularly during storms and hurricanes. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/IEWJAEkGeNk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">What goes into a coral reef?</span></figcaption>
</figure>
<p>But corals are quite <a href="https://scied.ucar.edu/learning-zone/climate-change-impacts/corals-and-climate">sensitive to warming water</a>. They host a microscopic symbiotic <a href="https://oceanservice.noaa.gov/education/tutorial_corals/coral02_zooxanthellae.html">algae called zooxanthella</a> that photosynthesizes just like plants, providing food to the coral. When the surrounding waters get too warm for too long, the zooxanthellae leave the coral, and the coral can turn pale or white – a process known as bleaching.</p>
<p>If corals stay bleached, they can become energetically compromised and ultimately die.</p>
<p>When corals die or their growth slows, these beautiful, complex reef habitats start disappearing and can eventually erode to sand. A recent paper by <a href="https://www.aoml.noaa.gov/tag/john-morris/">John Morris</a>, a scientist in my lab in Florida, shows that around <a href="https://doi.org/10.1038/s41598-022-23394-4">70% of reefs are now net erosional in the Florida Keys</a>, meaning they are losing more habitat than they build.</p>
<figure class="align-center ">
<img alt="Two maps show large areas of above average heat, particularly along the equator in the Pacific, which is an indicator of El Nino, and in much of the Atlantic." src="https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=670&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=670&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=670&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=842&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=842&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537391/original/file-20230713-21-xyfqps.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=842&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">About 40% of the global ocean was experiencing a marine heat wave in July 2023. NOAA’s experimental forecasts for August and October show sea surface temperatures well above average in many regions. An increase of 1 degree Celsius = 1.8 degrees Fahrenheit.</span>
<span class="attribution"><a class="source" href="https://psl.noaa.gov/marine-heatwaves/#report">NOAA PSL</a></span>
</figcaption>
</figure>
<p>Unfortunately, these critical coral reef habitats are in decline around the world because of extreme bleaching events, disease and numerous other human-caused stressors. In the Florida Keys, coral cover has decline by about <a href="https://www.climate.gov/news-features/features/mission-iconic-reefs-noaa-aims-restore-florida-keys-climate-resilient-corals">90% over the past several decades</a>.</p>
<h2>Coral bleaching in 2023</h2>
<p>In the Port of Miami, where we have found <a href="https://doi.org/10.1038/s41598-023-33467-7">particularly resilient coral communities</a>, a doctoral candidate in my lab, <a href="https://www.researchgate.net/profile/Allyson-Demerlis">Allyson DeMerlis</a>, documented the first coral bleaching of her experimentally <a href="https://reefresilience.org/management-strategies/restoration/coral-populations/coral-gardening/outplanting/">outplanted corals</a> on July 11, 2023.</p>
<p>Other scientists we work with have reported coral bleaching off of Colombia, El Salvador, Costa Rica and Mexico in the eastern Pacific, as well as along the Caribbean coasts of Panama, Mexico and Belize.</p>
<p>We have yet to see widespread coral death associated with this particular marine heat wave, so it is possible the corals could recover if sea surface temperatures cool down soon. However, global sea surface <a href="https://theconversation.com/ocean-heat-is-off-the-charts-heres-what-that-means-for-humans-and-ecosystems-around-the-world-207902">temperatures are at record highs</a>, and large parts of the Atlantic and eastern Pacific are <a href="https://coralreefwatch.noaa.gov/satellite/bleachingoutlook_cfs/index.php">under bleaching alerts</a>. At this point, the evidence points to the potential for a very negative outcome.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A chart of every year's global daily average sea surface temperature shows 2023 far above all other years since satellite records started in 1981." src="https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=382&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=382&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=382&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=480&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=480&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537387/original/file-20230713-29-3fo0qw.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=480&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Sea surface temperatures have been off the charts. The thick black line is 2023. The orange line is 2022. The 1982-2011 average is the middle dashed line.</span>
<span class="attribution"><a class="source" href="https://climatereanalyzer.org/clim/sst_daily/">ClimateReanalyzer.org/NOAA OISST v2.1</a></span>
</figcaption>
</figure>
<p><a href="https://theconversation.com/el-nino-is-back-thats-good-news-or-bad-news-depending-on-where-you-live-205974">El Niño</a> is contributing to the problem this year, but the longer-term trends of rising ocean heat are <a href="https://climate.nasa.gov/">driven by global warming</a> fueled by human activities.</p>
<p>To put that into context, <a href="https://doi.org/10.1038/srep16762">a paper</a> by NOAA scientist <a href="https://scholar.google.com/citations?user=rEv8BNoAAAAJ&hl=en">Derek Manzello</a> showed that in the Florida Keys, the number of days per year in which water temperatures were higher than 90 F (32 C) had increased by more than 2,500% in the two decades following the mid-1990s relative to the prior 20 years. That is a remarkable increase in the number of days that corals are experiencing particularly stressful warm water.</p>
<h2>What can we do to protect corals?</h2>
<p>First, we cannot give up on corals.</p>
<p><a href="https://www.aoml.noaa.gov/people/alice-webb/">Alice Webb</a>, a coral reef scientist working with our group, recently published <a href="https://doi.org/10.1038/s41598-022-26930-4">a study</a> based on years of our research in the Florida Keys. She modeled reef habitat persistence under climate, restoration and adaptation scenarios and found that protecting reefs is going to take everything – active restoration of reefs, helping corals acclimate or adapt to changing temperatures, and, importantly, human curbing of greenhouse gas emissions.</p>
<figure class="align-center ">
<img alt="A map shows warm ocean temperatures across a large part of the Atlantic and Pacific around North America." src="https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=504&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=504&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=504&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=634&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=634&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537410/original/file-20230713-17-5rc865.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=634&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Sea surface temperatures off South Florida were abnormally high in mid-July 2023.</span>
<span class="attribution"><a class="source" href="https://coralreefwatch.noaa.gov/product/5km/index_5km_sst.php">Coral Reef Watch/NOAA</a></span>
</figcaption>
</figure>
<p>Major restoration efforts are underway in the Florida Keys as part of the NOAA-led <a href="https://marinesanctuary.org/mission-iconic-reefs/">Mission Iconic Reefs</a>. We are also assessing how different coral individuals perform under stress, hoping to identify those that are particularly stress-tolerant by combing through the massive amounts of <a href="https://www.ingentaconnect.com/contentone/umrsmas/bullmar/2023/00000099/00000002/art00006">data from restoration projects and coral nurseries</a>.</p>
<p>We are also evaluating stress-hardening techniques. For example, in tide pools, corals are exposed to large swings in temperature over short periods, making them more resilient to subsequent thermal stress events. We are exploring whether it’s possible to replicate that natural process in the lab, before corals are planted onto reefs, to better <a href="https://doi.org/10.1007/s00338-022-02232-z">prepare them for stressful summers in the wild</a>.</p>
<p>Coral bleaching on a large scale has really been documented only since the early 1980s. When I talk to people who have been fishing and diving in the Florida Keys since before I was born, they have amazing stories of how vibrant the reefs used to be. They know firsthand how bad things have become because they have lived it.</p>
<p>There isn’t currently a single silver-bullet solution, but ignoring the harm being done is not an option. There is simply too much at stake.</p><img src="https://counter.theconversation.com/content/209770/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ian Enochs receives funding from NOAA. </span></em></p>Water temperatures in the 90s off Florida in July are alarming, a NOAA coral scientist writes. Scientists in several North American countries have already spotted coral bleaching off their coasts.Ian Enochs, Research Ecologist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2041182023-04-20T02:09:48Z2023-04-20T02:09:48ZEl Nino 2023 juga berdampak ke laut, bencana bagi ikan dan karang<figure><img src="https://images.theconversation.com/files/521803/original/file-20230419-241-vhiof.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Gelombang panas laut dapat mencapai dasar laut serta air permukaan. (Sebastian Pena Lambarri via Unsplash) CC BY</span> </figcaption></figure><p>Hembusan angin sepanjang Samudra Pasifik semakin lemah. Panas mulai merembes ke bawah permukaan laut. El Nino yang membawa udara kering ke bumi akan tiba. </p>
<p>Pada Juli nanti, <a href="https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/">hampir seluruh pemodelan memprediksi</a> bahwa raksasa dalam sistem iklim bumi, El Nino, akan kembali setelah empat tahun bersembunyi. </p>
<p>El Nino adalah sisi lain dari ‘koin iklim’ bernama <a href="https://www.climate.gov/news-features/understanding-climate/el-ni%C3%B1o-and-la-ni%C3%B1a-frequently-asked-questions">El Niño-Southern Oscillation, atau ENSO</a>. Sisi lainnya adalah La Nina yang membawa iklim basah ke bumi.</p>
<p>Selama El Nino, hamparan lautan yang membentang sekitar 10 ribu kilometer ke arah barat lepas pantai Ekuador akan menghangat selama berbulan-bulan. Kenaikan suhunya mencapai sekitar 1 hingga 2 °C.</p>
<p>Sepintas angka di atas terasa kecil. Namun, sebenarnya angka itu lebih dari cukup untuk merombak pola angin, curah hujan, dan suhu di seluruh planet.</p>
<figure class="align-center ">
<img alt="Pemutihan karang akibat perubahan iklim." src="https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.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">Gelombang panas laut dapat memicu pemutihan karang.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/view-of-major-bleaching-on-the-coral-reefs-of-the-society-news-photo/1148857683">Alexis Rosenfeld/Getty Images</a></span>
</figcaption>
</figure>
<p>Saya adalah ilmuwan iklim yang mempelajari lautan. Setelah <a href="https://earthobservatory.nasa.gov/images/150691/la-nina-times-three">tiga tahun berturut-turut</a> bumi dilanda <a href="https://oceanservice.noaa.gov/facts/ninonina.html">La Nina</a>, saatnya kita bersiap menghadapi dampak yang dapat disebabkan oleh El Nino.</p>
<h2>Bagaimana dampak El Nino terhadap bumi?</h2>
<p>Setiap kejadian El Nino pasti berbeda satu sama lain. Walau begitu, kita sudah bisa memprediksi apa yang <a href="https://www.weather.gov/images/fwd/climate/enso/ElNino.png">mungkin terjadi</a>.</p>
<p>Orang-orang cenderung berfokus pada dampak El Nino terhadap daratan. Fokus ini bisa dibenarkan karena udara hangat mempengaruhi aliran udara. Akibatnya, beberapa kawasan bisa lebih kering atau bahkan lebih basah dari biasanya. </p>
<p>El Nino bahkan memperkuat kejadian badai, seperti di wilayah selatan Amerika Serikat, sekaligus meredam amukan cuaca dari <a href="https://tropical.colostate.edu/Forecast/2023-04.pdf">Atlantik</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/wVlfyhs64IY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Bagaimana El Nino terjadi. NOAA.</span></figcaption>
</figure>
<p>El Nino juga dapat memporak-porandakan banyak ekosistem laut seperti <a href="https://theconversation.com/watching-a-coral-reef-die-as-climate-change-devastates-one-of-the-most-pristine-tropical-island-areas-on-earth-159792">terumbu karang</a> maupun <a href="https://theconversation.com/restoring-seagrasses-can-bring-coastal-bays-back-to-life-147798">padang lamun</a> yang menyokong sektor perikanan global.</p>
<p>Secara khusus, El Nino dapat menciptakan gelombang panas laut ekstrem secara intens dan lama. Hal ini dapat memperparah <a href="https://www.theguardian.com/environment/2023/apr/08/headed-off-the-charts-worlds-ocean-surface-temperature-hits-record-high?CMP=share_btn_tw">pemanasan suhu laut global</a> yang sudah mencapai <a href="https://climatereanalyzer.org/clim/sst_daily/">rekor tertinggi</a>. Karena itu, gelombang panas akibat El Nino bisa membawa sektor perikanan (yang sensitif terhadap cuaca) ke ujung tanduk.</p>
<h2>Petaka dari gelombang panas laut</h2>
<p>Gelombang panas laut adalah “gelombang” panas ekstrem yang terjadi di laut, mirip seperti yang terjadi di daratan.</p>
<p>Dampaknya tak bisa diremehkan. Gelombang berskala kecil saja bisa menghangatkan air laut di sekitar <a href="https://doi.org/10.1029/2019JC015673">teluk kecil maupun besar</a> selama beberapa hari ataupun pekan. </p>
<p>Sedangkan dampak gelombang berskala besar seperti <a href="https://doi.org/10.1002/2015GL063306">Northeast Pacific Warm Blob</a> pada 2013-2014 bisa memanaskan air laut hingga 2-3 °C di atas rata-rata selama berbulan-bulan bahkan bertahun-tahun. Gelombangnya sangat besar, dengan jangkauan setara <a href="https://indd.adobe.com/view/ffe33cde-3628-42e8-adc2-eaf85d8312e4">tiga kali luas wilayah Texas</a>.</p>
<figure class="align-center ">
<img alt="El Nino memanaskan laut." src="https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=363&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=363&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=363&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=456&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=456&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=456&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Gelombang panas ekstrem yang terjadi pada 2019 dapat menghancurkan kehidupan laut dengan pemanasan 2-3 °C di atas temperatur normal.</span>
<span class="attribution"><span class="source">Dillon Amaya</span></span>
</figcaption>
</figure>
<p>Air laut yang menghangat mungkin tak terlihat seperti masalah besar, khususnya bagi peselancar yang tak ingin menggunakan baju. Namun, bagi banyak makhluk laut yang hanya hidup di suhu tertentu, <a href="https://doi.org/10.1146/annurev-marine-032122-121437">gelombang panas laut dapat membuat mereka ‘gerah’ seperti habis lari maraton</a>.</p>
<p>Beberapa jenis ikan, misalnya, bisa mati karena metabolisme yang meningkat saat air menghangat. Proses ini menghabiskan energi lebih cepat dari kemampuan ikan ini melahap mangsa. </p>
<p>Ikan kod pasifik menjadi contoh. Populasi spesies ini berkurang hingga 70% di Teluk Alaska karena terkena gelombang panas laut. </p>
<p><a href="https://doi.org/10.1038/s41558-019-0412-1">Selain membahayakan ikan, gelombang panas laut</a> juga memutihkan karang, mengakibatkan ledakan alga berbahaya, merusak rumput laut, dan meningkatkan risiko hewan terdampar. <a href="https://www.annualreviews.org/doi/10.1146/annurev-marine-032122-121437">Kerugian akibat gelombang panas laut</a> bisa mencapai ratusan triliun rupiah setiap tahun.</p>
<p>Gelombang panas laut dapat menjadi pemicu berbagai <a href="https://doi.org/10.1038/s41467-019-10206-z">kejadian lainnya di laut.</a>. Terkadang arus laut menggeser arus laut hangat. Angin permukaan bisa lebih lemah dari biasanya, sehingga mengurangi penguapan air dari laut (evaporasi) ataupun perairan lainnya. </p>
<p>Suatu area juga bisa tidak terlalu mendung selama beberapa bulan, sehingga memungkinkan lebih banyak sinar matahari masuk dan memanaskan lautan. Terkadang angin yang lebih lemah dan lebih sedikit awan terjadi pada saat yang sama, menghasilkan <a href="https://doi.org/10.1038/s41467-020-15820-w">gelombang panas laut yang memecahkan rekor</a>..</p>
<h2>Efek El Nino yang beragam</h2>
<p>El Nino adalah ‘raja’ dalam sistem iklim bumi. Saat El Nino tiba, seisi Bumi akan terimbas, termasuk juga lautan.</p>
<p>Walau begitu, kemungkinan peningkatan gelombang panas karena El Nino akan bergantung di mana kamu berada.</p>
<p>Di sepanjang Pantai Barat Amerika Serikat, angin permukaan yang biasa berhembus dari utara akan melemah selama El Nino. Hal ini turut meredam evaporasi dan memperlambat <a href="https://oceanservice.noaa.gov/education/tutorial_currents/03coastal4.html">aliran air dingin dari bawah laut ke arah permukaan (<em>upwelling</em>)</a>. Kejadian ini meningkatkan peluang gelombang panas laut di kawasan pesisir.</p>
<p><iframe id="17ZbA" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/17ZbA/4/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Berabad-abad silam, para nelayan Peru telah menghitung periode pemanasan laut ekstrem yang membuat ikan-ikan kabur. <a href="https://earthobservatory.nasa.gov/features/ElNino/page3.php">Pada dekade 1920-an</a> para ilmuwan baru menyadari gelombang panas laut di Amerika Selatan ini terkait dengan ENSO di kawasan Pasifik.</p>
<p>Di Teluk Benggala, sebelah timur India, interaksi El Nino dengan aliran udara tropis <a>(disebut juga <em>Walker Circulation</em>)</a> juga meningkatkan risiko gelombang panas laut.</p>
<h2>Risiko menghantui di dasar laut</h2>
<p>Sekalipun gelombang panas lebih terasa di permukaan laut tahun ini, area bawah laut pun tidak akan baik-baik saja.</p>
<p>Dalam <a href="https://doi.org/10.1038/s41467-023-36567-0">studi terbaru</a>, saya bersama kolega menunjukkan bahwa gelombang panas laut juga terjadi di dasar laut kawasan pesisir. </p>
<p>Faktanya, gelombang panas bawah laut terkadang lebih intens dibandingkan di permukaan. Gelombang ini juga bisa bertahan lebih lama. Contohnya, gelombang panas bawah laut selama 19997-1998 di Pantai Barat Amerika Serikat berlangsung 4-5 bulan lebih lama dibandingkan temperatur di bagian permukaan laut.</p>
<p>Kejadian yang dapat berhubungan dengan El Nino ini dapat menimbulkan tekanan bagi makhluk dasar laut. Stok kepiting salju di Laut Bering misalnya, yang anjlok 84% pada 2018 kala gelombang panas mencapai dasar laut.</p>
<h2>Bersiap menghadapi gelombang panas</h2>
<p>El Nino di depan mata. Apa yang akan terjadi tahun ini?</p>
<p>Kabar baiknya, <a href="https://doi.org/10.1038/s41586-022-04573-9">model peramalan musim bisa memprediksi gelombang panas laut lebih baik</a>, sekitar 3-6 bulan sebelumnya, tergantung lokasinya. Sepanjang tahun El Nino, ramalan ini cenderung lebih akurat.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Peta pemanasan laut pada 2023." src="https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=292&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=292&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=292&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=367&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=367&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=367&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ramalan gelombang panas laut NOAA yang terbit pada awal April memprediksi kejadian pada Oktober 2023.</span>
<span class="attribution"><a class="source" href="https://psl.noaa.gov/marine-heatwaves/">NOAA/Jacox, et al. 2022</a></span>
</figcaption>
</figure>
<p><a href="https://psl.noaa.gov/marine-heatwaves/">Ramalan terbaru</a> memprediksi beberapa gelombang panas aktif bertahan selama Juni-Agustus, seperti di Pasifik Utara, lepas pantai Peru, sebelah tenggara Selandia Baru, dan kawasan tropis di Atlantik Utara.</p>
<p>Ramalan yang sama juga memprediksi El Nino akan menguat pada 6-9 bulan mendatang. Ini meningkatkan risiko gelombang panas selama Januari-Maret 2024 di Pantai Barat Amerika Serikat, Samudra India sebelah barat, Teluk Benggala, dan kawasan tropis Atlantik Utara.</p>
<p>Prediksi ini mungkin bisa berubah. Waktulah yang akan menjawab apakah gelombang ini akan membawa uap panas. Setidaknya kita sudah mengetahuinya dan waspada menunggu datangnya El Nino.</p><img src="https://counter.theconversation.com/content/204118/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dillon Amaya tidak bekerja, menjadi konsultan, memiliki saham, atau menerima dana dari perusahaan atau organisasi mana pun yang akan mengambil untung dari artikel ini, dan telah mengungkapkan bahwa ia tidak memiliki afiliasi selain yang telah disebut di atas.</span></em></p>El Nino dapat memperkuat sekaligus memperluas gelombang panas laut ekstrem yang dapat menghancurkan kehidupan perairanDillon Amaya, Climate Research Scientist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2024242023-04-18T12:44:48Z2023-04-18T12:44:48ZEl Niño is coming, and ocean temps are already at record highs – that can spell disaster for fish and corals<figure><img src="https://images.theconversation.com/files/521111/original/file-20230414-14-kbsx6w.jpg?ixlib=rb-1.1.0&rect=10%2C3%2C2385%2C1591&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Marine heat waves can reach the ocean floor as well as surface waters.</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/YV593oyMKmo">Sebastian Pena Lambarri via Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>It’s coming. Winds are weakening along the equatorial Pacific Ocean. Heat is building beneath the ocean surface. By July, <a href="https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/">most forecast models agree</a> that the climate system’s biggest player – El Niño – will return for the first time in nearly four years.</p>
<p>El Niño is one side of the climatic coin called the <a href="https://www.climate.gov/news-features/understanding-climate/el-ni%C3%B1o-and-la-ni%C3%B1a-frequently-asked-questions">El Niño-Southern Oscillation, or ENSO</a>. It’s the heads to La Niña’s tails.</p>
<p>During El Niño, a swath of ocean stretching 6,000 miles (about 10,000 kilometers) westward off the coast of Ecuador warms for months on end, typically by 2 to 4 degrees Fahrenheit (about 1 to 2 degrees Celsius). A few degrees may not seem like much, but in that part of the world, it’s more than enough to completely reorganize wind, rainfall and temperature patterns all over the planet.</p>
<figure class="align-center ">
<img alt="White corals indicate bleaching from heat stress." src="https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521376/original/file-20230417-26-ukagro.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">Marine heat waves can trigger coral bleaching.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/view-of-major-bleaching-on-the-coral-reefs-of-the-society-news-photo/1148857683">Alexis Rosenfeld/Getty Images</a></span>
</figcaption>
</figure>
<p>I’m a climate scientist who studies the oceans. After <a href="https://earthobservatory.nasa.gov/images/150691/la-nina-times-three">three years</a> of <a href="https://oceanservice.noaa.gov/facts/ninonina.html">La Niña</a>, it’s time to start preparing for what El Niño may have in store.</p>
<h2>How El Niño affects the planet</h2>
<p>No two El Niño events are exactly alike, though we’ve seen enough of them that forecasters have a pretty good idea of <a href="https://www.weather.gov/images/fwd/climate/enso/ElNino.png">what’s likely to happen</a>.</p>
<p>People tend to focus on El Niño’s impact on land, justifiably. The warm water affects air currents that leave areas wetter or drier than usual. It can ramp up storms in some areas, like the southern U.S., while <a href="https://tropical.colostate.edu/Forecast/2023-04.pdf">tending to tamp down Atlantic hurricane activity</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/wVlfyhs64IY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How El Niño forms. NOAA.</span></figcaption>
</figure>
<p>El Niño can also wreak havoc on the many marine ecosystems that support the world’s fishing industries, including <a href="https://theconversation.com/watching-a-coral-reef-die-as-climate-change-devastates-one-of-the-most-pristine-tropical-island-areas-on-earth-159792">coral reefs</a> and <a href="https://theconversation.com/restoring-seagrasses-can-bring-coastal-bays-back-to-life-147798">seagrass meadows</a>.</p>
<p>Specifically, El Niño tends to trigger intense and widespread periods of extreme ocean warming known as marine heat waves.</p>
<p><a href="https://www.theguardian.com/environment/2023/apr/08/headed-off-the-charts-worlds-ocean-surface-temperature-hits-record-high?CMP=share_btn_tw">Global ocean temperatures</a> are already <a href="https://climatereanalyzer.org/clim/sst_daily/">at record highs</a>, so El Niño-induced marine heat waves could push many sensitive fisheries to a breaking point.</p>
<h2>The problem with marine heat waves</h2>
<p>A marine heat wave is just that: a “wave” of extreme heat in the ocean, not dissimilar to an atmospheric heat wave on land. </p>
<p>At their smallest, marine heat waves can inundate <a href="https://doi.org/10.1029/2019JC015673">local bays and coves</a> with hotter-than-normal water for a few days or weeks. At their largest, marine heat waves like the <a href="https://doi.org/10.1002/2015GL063306">Northeast Pacific Warm Blob</a> of 2013-2014 can grow to gargantuan proportions, with regions <a href="https://indd.adobe.com/view/ffe33cde-3628-42e8-adc2-eaf85d8312e4">three times the size of Texas</a> experiencing ocean temperatures 4 to 6 F (about 2 to 3 C) above average for months or even years.</p>
<figure class="align-center ">
<img alt="An example of a marine heat wave showing intense heat." src="https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=363&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=363&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=363&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=456&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=456&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521094/original/file-20230414-24-5gh4an.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=456&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Fierce marine heat waves like this one in 2019 can wreak havoc on sea life off the North American Pacific Coast with temperatures about 4 to 6 F (2 to 3 C) above normal.</span>
<span class="attribution"><span class="source">Dillon Amaya</span></span>
</figcaption>
</figure>
<p>Warm water might not seem like a big deal, especially to surfers hoping to leave their wetsuits at home. But for many marine organisms that are highly adapted to specific water temperatures, <a href="https://doi.org/10.1146/annurev-marine-032122-121437">marine heat waves can make living in the ocean feel like running a marathon</a>.</p>
<p>For example, some fish increase their metabolism in warm waters by so much that they burn energy faster than they can eat, and they can die. Pacific cod declined by 70% in the Gulf of Alaska in response to a marine heat wave. <a href="https://doi.org/10.1038/s41558-019-0412-1">Other impacts</a> include bleached corals, widespread harmful algal blooms, decimated seaweeds and increased marine mammal strandings. All told, <a href="https://www.annualreviews.org/doi/10.1146/annurev-marine-032122-121437">billions of U.S. dollars are lost</a> to marine heat waves each year.</p>
<p>Marine heat waves flare up for a <a href="https://doi.org/10.1038/s41467-019-10206-z">variety of reasons</a>. Sometimes ocean currents shift warm water around. Sometimes surface winds are weaker than normal, leading to less evaporation over the ocean and warmer waters. Sometimes cloudy places just aren’t as cloudy for a few months, which lets more sunlight in and heats up the ocean. Sometimes both weaker winds and fewer clouds happen at the same time, producing <a href="https://doi.org/10.1038/s41467-020-15820-w">record-breaking marine heat waves</a>.</p>
<h2>Where El Niño fits in</h2>
<p>In the climate system, El Niño is king. When it dons its fiery crown, the entire planet takes notice, and the oceans are no exception. But the likelihood of increased marine heat wave activity during El Niño depends on where you are.</p>
<p>Along the U.S. West Coast during El Niño, surface winds that normally blow from the north tend to subside. This weakens evaporation and <a href="https://oceanservice.noaa.gov/education/tutorial_currents/03coastal4.html">slows upwelling</a> of colder, deeper water. That increases the chances of coastal marine heat waves.</p>
<p><iframe id="17ZbA" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/17ZbA/4/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Peruvian fishers have for centuries weathered periods of extreme ocean warming that drive fish away. <a href="https://earthobservatory.nasa.gov/features/ElNino/page3.php">It wasn’t until the 1920s</a> that scientists realized that these South American marine heat waves were related to the Pacificwide ENSO.</p>
<p>In the Bay of Bengal east of India, interactions between El Niño and a tropical air flow pattern known as the <a href="https://www.climate.gov/news-features/blogs/enso/walker-circulation-ensos-atmospheric-buddy">Walker Circulation</a> elevate the risk for marine heat waves.</p>
<h2>Seafloor heat waves are another risk</h2>
<p>Even if marine heat waves aren’t more obvious at the ocean surface this year, it doesn’t mean all is well down below.</p>
<p>In a <a href="https://doi.org/10.1038/s41467-023-36567-0">recent study</a>, my colleagues and I showed that marine heat waves also unfold along the seafloor of coastal regions. In fact, these “bottom marine heat waves” are sometimes more intense than their surface counterparts. They can also persist much longer. For example, a 1997-1998 bottom marine heat wave off the U.S. West Coast lasted an extra four to five months after surface ocean temperatures had already cooled.</p>
<p>Events like this can be related to El Niño and put a lot of stress on bottom-dwelling species. Bering Sea snow crab landings were down 84% in 2018 after a marine heat wave reached the seafloor.</p>
<h2>We’re in (for) hot water</h2>
<p>With El Niño on the horizon, what can we expect for this year?</p>
<p>The good news is <a href="https://doi.org/10.1038/s41586-022-04573-9">seasonal forecast models can skillfully predict marine heat waves</a> three to six months in advance, depending on the region. And forecasts tend to be most accurate during El Niño years.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Map showing where marine heat waves are forecast in October 2023." src="https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=292&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=292&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=292&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=367&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=367&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521512/original/file-20230418-28-f96w6.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=367&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">NOAA’s marine heat wave forecast issued in early April predicting October 2023.</span>
<span class="attribution"><a class="source" href="https://psl.noaa.gov/marine-heatwaves/">NOAA/Jacox, et al. 2022</a></span>
</figcaption>
</figure>
<p><a href="https://psl.noaa.gov/marine-heatwaves/">The latest forecast</a> predicts several active marine heat waves to persist into June-August, including in the North Pacific, off the coast of Peru, southeast of New Zealand and in the tropical North Atlantic.</p>
<p>The same forecasts predict El Niño to ramp up over the next six to nine months, increasing marine heat wave risk in January to March of 2024 for the U.S. West Coast, the western Indian Ocean, the Bay of Bengal, and the tropical North Atlantic. </p>
<p>That said, these predictions are far enough out that things could change. Time will tell whether they hold (hot) water, but we would do well to prepare. El Niño is coming.</p><img src="https://counter.theconversation.com/content/202424/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dillon Amaya does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>El Niño can trigger intense and widespread periods of extreme ocean warming known as marine heat waves. They can devastate marine life.Dillon Amaya, Climate Research Scientist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1539582021-02-09T13:31:58Z2021-02-09T13:31:58ZWhat exactly is the polar vortex?<figure><img src="https://images.theconversation.com/files/383080/original/file-20210208-21-1egxafb.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2928%2C1619&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The polar vortex influences the jet stream, which can bring cold winter weather to the U.S. and Europe. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/WinterWeatherMassachusetts/6268c1f80afb42b69b2f8f6ab03ce728/photo?Query=snowstorm%202021&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=157&currentItemNo=3">AP Photo/Bill Sikes</a></span></figcaption></figure><p>At the start of February 2021, <a href="https://weather.com/news/news/2021-02-02-new-england-northeast-winter-storm-orlena-impacts">a major snowstorm hit the northeast United States</a>, with some areas receiving well over <a href="https://www.washingtonpost.com/weather/2021/02/02/winter-storm-snow-northeast-mid-atlantic/">two feet of snow</a>. Just a few weeks earlier, Spain experienced <a href="https://www.theguardian.com/world/2021/jan/09/army-rescues-motorists-after-storm-filomena-blankets-spain-in-snow">a historic and deadly snowstorm</a> and <a href="https://www.bbc.com/news/world-europe-55632791">dangerously low temperatures</a>. Northern Siberia is no stranger to cold, but in mid-January 2021, <a href="https://www.accuweather.com/en/winter-weather/extreme-cold-sends-temperatures-plummeting-to-73-below-zero-in-siberia/883874">some Siberian cities</a> reported temperatures below minus 70 F (minus 56 C). Media headlines hint that <a href="https://www.masslive.com/weather/2021/01/near-blizzard-conditions-forecast-on-cape-cod-as-polar-vortex-moves-through-massachusetts-light-snow-expected-elsewhere-along-the-coast.html">the polar vortex has arrived</a>, as if it were some sort of ice tornado that wreaks wintry havoc wherever it strikes.</p>
<p>As <a href="https://scholar.google.com/citations?user=uUvgRSQAAAAJ&hl=en&oi=ao">atmospheric</a> <a href="https://scholar.google.com/citations?hl=en&user=Eck4ZyIAAAAJ">scientists</a>, we cringe when the term polar vortex is used to loosely refer to blasts of cold weather. The actual <a href="https://www.climate.gov/news-features/blogs/enso/polar-vortex-going-make-you-put-sweater-be-afraid-be-very-afraid">polar vortex</a> can’t put snow in your backyard, but changes in the polar vortex can load the dice for wintry weather – and this year, the dice rolled Yahtzee. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/383093/original/file-20210208-15-b798v4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A man skies through Times Square in New York City." src="https://images.theconversation.com/files/383093/original/file-20210208-15-b798v4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/383093/original/file-20210208-15-b798v4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/383093/original/file-20210208-15-b798v4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/383093/original/file-20210208-15-b798v4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/383093/original/file-20210208-15-b798v4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/383093/original/file-20210208-15-b798v4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/383093/original/file-20210208-15-b798v4.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 weak polar vortex in early 2021 created a curvy jet stream that brought cold and winter storms to the northeastern U.S.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/APTOPIXWinterWeatherNewYork/8ffc56de84bc45faa388bbeb6ecc7cb5/photo?Query=snowstorm%202021&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=157&currentItemNo=1">AP Photo/John Minchillo</a></span>
</figcaption>
</figure>
<h2>The winds of winter</h2>
<p>The polar vortex is an enormous, three-dimensional ring of winds that surrounds the North and South poles during each hemisphere’s winter. These winds are located about 10 to 30 miles (16 to 50 kilometers) above Earth’s surface, in the layer of the atmosphere known as the <a href="https://scied.ucar.edu/learning-zone/atmosphere/stratosphere-overview">stratosphere</a>. They blow from west to east with sustained speeds easily exceeding 100 mph (160 kph). In the darkness of the <a href="https://theconversation.com/arctic-ocean-climate-change-is-flooding-the-remote-north-with-light-and-new-species-150157">winter polar night</a>, temperatures within the polar vortex can easily get lower than minus 110 F (minus 79 C). </p>
<p>Fortunately for everyone, the stratospheric polar vortex itself won’t appear outside your front door. The polar vortex does influence winter weather, but it is more like a domino – when it is knocked over, it can start a chain of events that later result in wild weather. </p>
<p>The strength of the polar vortex can vary widely during winter, and these variations can lead to shifts in the strength and position of the <a href="https://scijinks.gov/jet-stream/">jet stream</a>, the fast-flowing river of air in the troposphere beneath the polar vortex. When the jet stream changes, it affects the movement of weather systems, causing different parts of the world to see much warmer or colder, or much wetter or drier conditions. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/I_htSntkNaA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The disruption of the polar vortex during the beginning of 2021 was dramatic. Zachary Lawerence/CIRES/NOAA.</span></figcaption>
</figure>
<h2>The domino effect</h2>
<p>Since the Earth’s atmosphere is one giant shell of air that moves like a fluid, the polar vortex is interconnected with the weather that moves around the Earth at lower altitudes. Normal variations in the jet stream and weather can disturb the structure of the vortex in the stratosphere. Like an elastic band, the vortex usually rebounds back to its normal shape and size, maintaining its strong winds and low temperatures.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/383120/original/file-20210208-17-da9ac4.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two side by side images showing the polar vortex as a nice circle over the north pole and another one showing it offset and deformed into an L-shape." src="https://images.theconversation.com/files/383120/original/file-20210208-17-da9ac4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/383120/original/file-20210208-17-da9ac4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/383120/original/file-20210208-17-da9ac4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/383120/original/file-20210208-17-da9ac4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/383120/original/file-20210208-17-da9ac4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/383120/original/file-20210208-17-da9ac4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/383120/original/file-20210208-17-da9ac4.png?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">Between December (left) and January (right), the polar vortex moved entirely off the North Pole and lost much of its structural integrity.</span>
<span class="attribution"><span class="source">Zachary Lawrence/CIRES/NOAA</span></span>
</figcaption>
</figure>
<p>But sometimes, these weather and jet stream variations can knock the polar vortex off balance, causing significant wobbles in its shape, location, temperatures and winds. When this happens, the structural integrity of the polar vortex begins to break down. If this happens often enough over a period of time, everything can go haywire with the polar vortex as the winds break down and the vortex warms up.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/383119/original/file-20210208-13-qg74jv.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Side by side images showing a relatively circular jet stream and a very wavy jet stream." src="https://images.theconversation.com/files/383119/original/file-20210208-13-qg74jv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/383119/original/file-20210208-13-qg74jv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/383119/original/file-20210208-13-qg74jv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/383119/original/file-20210208-13-qg74jv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/383119/original/file-20210208-13-qg74jv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/383119/original/file-20210208-13-qg74jv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/383119/original/file-20210208-13-qg74jv.png?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">As the polar vortex deforms between December and January, the jet stream became much wavier and brought cold storms farther south.</span>
<span class="attribution"><span class="source">Zachary Lawrence/CIRES/NOAA</span></span>
</figcaption>
</figure>
<p>This is precisely what has unfolded this year: On Jan. 5, the polar vortex was completely thrown out of whack by an event called a <a href="https://www.climate.gov/news-features/blogs/enso/sudden-stratospheric-warming-and-polar-vortex-early-2021">sudden stratospheric warming</a>. <a href="https://doi.org/10.1029/2020RG000708">Sudden stratospheric warming</a> is the technical name for these violent disturbances that severely distort and weaken the vortex, knocking it off of the pole or even ripping it apart. When this happens, temperatures in the normally cold polar stratosphere explosively rise by as much as 90 F (50 C) over the span of a few days – hence the name of these events. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1084935021171924992"}"></div></p>
<p>At this point, the domino has tipped over: Eventually the jet stream feels the effects of the weakened polar vortex above, and it can begin to undulate. When the jet stream gets wavy, it can dip farther south, bringing cold air and winter storms with it.</p>
<p>The January 2021 event pushed the polar vortex from its normal position over the North Pole all the way over to Europe and Siberia, nearly pulling it apart multiple times in the process. It can take weeks or months for the polar vortex to recover from something like this. While the vortex pieces itself back together, the undulating, curvy jet stream can bring frigid Arctic air and winter storms to the U.S. and Europe while allowing unusually warm weather to get into the far north. </p>
<h2>A strong polar vortex means warmer, not colder, weather</h2>
<p>In some winters, weather systems barely affect the polar vortex at all, allowing the vortex to grow colder with faster winds. This can have the opposite effect on the jet stream, causing it to keep cold Arctic air from the polar regions locked up north. This is what happened during the Northern Hemisphere winter of 2020, when the <a href="https://eos.org/research-spotlights/an-extraordinary-winter-in-the-polar-north">polar vortex was extraordinarily strong</a> and many regions <a href="https://www.economist.com/graphic-detail/2020/03/28/the-northern-hemisphere-winter-of-2019-20-was-the-warmest-ever-on-land">experienced an exceptionally warm and mild winter</a>. </p>
<p>Calling any blast of cold air a polar vortex is wrong. The behavior of the polar vortex doesn’t just portend colder weather – it can also foreshadow much warmer weather. Most of the time the polar vortex has little influence on winter weather as it flows like normal, miles above the surface. But forecasting and monitoring huge disturbances to the polar vortex allows us to anticipate the chain of events that may leave feet of snow and frigid weather at your doorstep.</p>
<p>[<em>The Conversation’s science, health and technology editors pick their favorite stories.</em> <a href="https://theconversation.com/us/newsletters/science-editors-picks-71/?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=science-favorite">Weekly on Wednesdays</a>.]</p><img src="https://counter.theconversation.com/content/153958/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Zachary Lawrence has received funding from NOAA. </span></em></p><p class="fine-print"><em><span>Amy Butler has received funding from NOAA and NSF.</span></em></p>The media often call unusually cold, snowy storms a ‘polar vortex.’ The real polar vortex isn’t coming down to visit the lower 48, but changes to the polar vortex can influence winter weather.Zachary Lawrence, Research Scientist, University of Colorado BoulderAmy Butler, Chemistry & Climate Processes Research Scientist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1194992019-07-22T10:55:31Z2019-07-22T10:55:31ZWaiting for an undersea robot in Antarctica to call home<figure><img src="https://images.theconversation.com/files/281448/original/file-20190626-76705-w53a62.jpg?ixlib=rb-1.1.0&rect=0%2C310%2C5184%2C3135&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">One of two underwater gliders is deployed from a research ship into Antarctic waters.</span> <span class="attribution"><span class="source">NOAA</span></span></figcaption></figure><p>“Call! Just call!” I think loudly in my head. “Did something happen? Are you okay?”</p>
<p>I might seem like a worried parent waiting for a teenager to report in from an unsupervised outing. Rather, I’m a <a href="https://www.linkedin.com/in/jenmariewalsh">research biologist</a> with the Antarctic Ecosystem Research Division at the National Oceanic and Atmospheric Administration. It’s late February 2019, and I am waiting for an autonomous underwater glider in Antarctica to surface and call me via satellite, so I can give it new diving instructions. The longest it’s supposed to go without surfacing is eight hours, and it’s now been nine.</p>
<p>Did it get stuck under an iceberg? An underwater ledge? I feel so helpless; I’m 9,000 miles away in San Diego and all I can do is chew my fingernails and think, “No. This can’t happen. We can’t lose this glider so close to the end.” </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/281837/original/file-20190628-94720-cx387f.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/281837/original/file-20190628-94720-cx387f.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/281837/original/file-20190628-94720-cx387f.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=565&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281837/original/file-20190628-94720-cx387f.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=565&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281837/original/file-20190628-94720-cx387f.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=565&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281837/original/file-20190628-94720-cx387f.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=711&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281837/original/file-20190628-94720-cx387f.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=711&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281837/original/file-20190628-94720-cx387f.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=711&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 survey area where gliders measured Antarctic krill populations.</span>
<span class="attribution"><span class="source">NOAA</span></span>
</figcaption>
</figure>
<p>Our research team is two-and-a-half months into a three-month-long mission just north of the Antarctic Peninsula. This is our first time deploying gliders so far from home, and our hope for a successful field season – not to mention a great deal of research – depends on recovering the two gliders our group deployed in December 2018. The gliders are now full of oceanographic data that will help us provide scientific advice on how best to conserve the Antarctic ecosystem as the area around the peninsula warms faster than almost any other region on Earth, which may adversely affect the animals that live there.</p>
<h2>9 hours, 30 minutes: No call</h2>
<p>For over 30 years, the <a href="https://swfsc.noaa.gov/textblock.aspx?id=551&ParentMenuId=42">NOAA group I’m part of</a> has conducted studies to estimate how many Antarctic krill, small shrimp-like creatures that support the diverse Antarctic food web, live around the Antarctic Peninsula.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/281449/original/file-20190626-76734-1ycpivt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/281449/original/file-20190626-76734-1ycpivt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281449/original/file-20190626-76734-1ycpivt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=467&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281449/original/file-20190626-76734-1ycpivt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=467&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281449/original/file-20190626-76734-1ycpivt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=467&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281449/original/file-20190626-76734-1ycpivt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=586&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281449/original/file-20190626-76734-1ycpivt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=586&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281449/original/file-20190626-76734-1ycpivt.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">Antarctic krill, <em>Euphausia superba</em>, can grow up to about 2.5 inches long.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Krill666.jpg">Uwe Kils/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Krill feeds penguins and seals that breed in this area every summer and whales and fishes that feed here year-round, while also supporting a major fishery. You may have seen bright-red dietary supplements made from krill oil prominently displayed at the pharmacy. Our data help establish catch limits for the krill fishery, ensuring enough krill remain in the ocean to maintain the population after all people and animals take what they need to make a living. Without good data to support fishery-management decisions, krill fishing could <a href="https://www.ccamlr.org/en/fisheries/krill-%E2%80%93-biology-ecology-and-fishing">undermine the food web</a> for which Antarctica is so well known, as demand for supplements and other <a href="https://bestmarketherald.com/krill-oil-market-demand-expected-to-raise-by-dietary-supplements-segment-in-upcoming-years/">krill products surges</a>.</p>
<h2>10 hours: No call</h2>
<p>Until three years ago, my program chartered a research vessel for a month each year to sail around the Antarctic Peninsula and <a href="https://swfsc.noaa.gov/contentblock.aspx?ID=14326&ParentMenuId=42">estimate the biomass of krill</a>. But after 2016, rising vessel costs eliminated our surveys. For our program to continue, we had to find a creative way to collect our data in Antarctica without actually going to Antarctica. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/281776/original/file-20190628-94724-w5a3pn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/281776/original/file-20190628-94724-w5a3pn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/281776/original/file-20190628-94724-w5a3pn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281776/original/file-20190628-94724-w5a3pn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281776/original/file-20190628-94724-w5a3pn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281776/original/file-20190628-94724-w5a3pn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281776/original/file-20190628-94724-w5a3pn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281776/original/file-20190628-94724-w5a3pn.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">An autonomous glider in the ocean.</span>
<span class="attribution"><span class="source">NOAA</span></span>
</figcaption>
</figure>
<p>Our solution was to use autonomous underwater gliders, which can be deployed in just a few hours by a small team from a ship in Antarctica, and then recovered months later. Gliders can dive to 3,000 feet, cover thousands of miles and follow commands from anywhere in the world with a laptop and an internet connection. Their batteries last six months, which means that they can collect much more data for much less money than a bunch of scientists on a research vessel. </p>
<p>The gliders resemble torpedoes in appearance, but contain three massive batteries and an array of scientific sensors that collect much of the same data we used to collect from a ship. Although the gliders are able to transmit small amounts of data via satellite throughout the deployment, the most valuable data are stored on the glider. If we lose a glider, which is always a possibility when you let something roam free in the ocean unattended for months, then we also lose the data.</p>
<p>We had effectively replaced ourselves with drones. But would they work?</p>
<h2>12 hours: No call</h2>
<p>For most of our team, the transition just a year ago from annual research voyages to the aquatic versions of C-3PO and R2-D2 was exciting. Secretly, though, I was terrified. I had spent my career as a scientist collecting krill samples from research vessels for biochemical analyses of their tissues. Suddenly I found myself ousted by oceanographic robots full of cables, wires, circuit boards and all sorts of other technological gadgetry.</p>
<p>These are not what you’d call smart robots. A bit like human toddlers, they have some degree of self-awareness, but would destroy themselves without semi-constant monitoring and instructions on how deep to dive or where to go. Outside supervision is especially important in the Southern Ocean, which is full of seamounts, canyons, strong currents and, most importantly, icebergs. </p>
<p>You can’t glider-proof the ocean the way you can baby-proof a house, so I had to forget everything I knew about biochemistry and learn as much as I could about glider piloting in 10 short months.</p>
<h2>13 hours: No call</h2>
<p>All that training and practice felt like 10 minutes by the time we finally packed up the gliders and shipped them to the Southern Hemisphere for their first Antarctic deployments. The commands for how deep to dive and where to go seemed simple enough, but the gliders responded as unpredictably as the ocean itself. </p>
<p>A near-disastrous practice deployment in San Diego revealed how slowly they maneuver, particularly in strong currents. Piloting them felt like trying to drive a remote-control semi-truck through a go-kart course, which reinforced our apprehension about driving these things through the ocean all the way across the planet, in one of the most remote and treacherous oceans on Earth.</p>
<p>Never mind the wind and the currents and the icebergs. What made this deployment far scarier was that if things started to go horribly wrong, we had no way to get the gliders back. It was like dropping a toddler off at college on another continent: What if he needs you and you can’t get to him?</p>
<h2>14 hours: No call</h2>
<p>Almost exactly 10 months from our first day of glider training, we carried the gliders across the Drake Passage on a research vessel bound for the Antarctic Peninsula. The deployments were flawless, and over the next few days, our confidence began to build. We quickly learned that icebergs were enemy number one, and they were formidable opponents. Satellite images of icebergs were <a href="https://www.polarview.aq/antarctic">available every couple of days</a>, and we overlaid maps of planned glider tracks onto those images so we could steer the gliders around any ice in their way. The trouble was, even the newest images we received were already a day old, and the ice had already moved.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/281839/original/file-20190628-94708-1yfhkyg.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/281839/original/file-20190628-94708-1yfhkyg.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/281839/original/file-20190628-94708-1yfhkyg.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=312&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281839/original/file-20190628-94708-1yfhkyg.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=312&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281839/original/file-20190628-94708-1yfhkyg.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=312&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281839/original/file-20190628-94708-1yfhkyg.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=392&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281839/original/file-20190628-94708-1yfhkyg.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=392&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281839/original/file-20190628-94708-1yfhkyg.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=392&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">On this chart of the South Shetland Islands, one intended glider path is marked in straight gray lines. Circled in red in the middle is the iceberg the researchers called ‘Yacu.’</span>
<span class="attribution"><span class="source">NOAA</span></span>
</figcaption>
</figure>
<p>Smaller icebergs were usually avoidable, but around three weeks into the deployment, “Yacu” appeared on the scene. Inspired by a <a href="http://www.salem-news.com/articles/august162010/monster-amazon-ta.php">mythological South American snake</a> that eats everything in its way, that was the nickname we gave a 12.5-mile-wide iceberg from the Weddell Sea that drifted right into the path of one of the gliders. Yacu stuck around for the rest of the deployment, every few days spawning smaller (but still huge) icebergs that posed a constant and unpredictable threat to gliders already at the mercy of currents, tides and wind.</p>
<p>If a glider gets trapped under an obstacle and senses that it’s been underwater for too long, it drops an emergency weight to rocket itself to the surface for an immediate recovery. Once a glider drops its weight, it can’t dive anymore. So if it is trapped under ice, it’s likely to stay trapped under ice. And one way to know if a glider is trapped is that it stops calling in, because it can connect to satellites only when it’s at the surface.</p>
<h2>15 hours: No call</h2>
<p>And then…</p>
<p>Ding ding! Ding ding! My laptop screams at me after 16 long hours: The glider is at the surface.</p>
<p>It is well past 9 p.m., but every member of our five-person team has been glued to a computer since early afternoon, and we collectively sigh with relief. We now think the glider probably surfaced after the first eight hours, failed to connect to the satellite and resumed diving, which can occasionally happen. The reason for the gap is unimportant compared to our elation. A couple of weeks later, we successfully recovered both gliders on schedule and completed our first autonomous Antarctic field season. </p>
<p>One key finding is that we can, in fact, replace a vessel-based fishery assessment with a glider-based one in less than a year. With gliders, we can get krill biomass estimates comparable to those we would expect from a ship. That means we can use gliders to continue to provide critical data for managing the krill fishery.</p>
<p>This is a profound accomplishment for us and for NOAA, and it also has far-reaching promise for the future of fisheries research globally. The cost of science keeps going up, and autonomous instruments offer an affordable way to collect critical data for effectively managing ocean resources and conserving fragile marine ecosystems worldwide. </p>
<p>Our gliders are like toddlers in one final way: They’re advanced technology, yet they’re still in their infancy. Their ongoing usefulness to understand our changing planet in real time will depend on new sensors and instruments yet to be developed. What we accomplished is only the the tip of Yacu compared to what the future of autonomous oceanographic research holds.</p><img src="https://counter.theconversation.com/content/119499/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jennifer Walsh is employed and funded by the U.S. National Oceanic and Atmospheric Administration. The scientific results and conclusions, as well as any views or opinions expressed herein, are those of the author(s) and do not necessarily reflect the views of NOAA or the Department of Commerce.</span></em></p>Sending autonomous vehicles to the Southern Ocean can be fraught with anxiety, especially if one of them doesn’t make radio contact when it’s supposed to.Jennifer Walsh, Research Biologist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1144332019-03-31T19:14:20Z2019-03-31T19:14:20ZBleaching has struck the southernmost coral reef in the world<p>This month corals in Lord Howe Island Marine Park began showing signs of bleaching. The 145,000 hectare marine park contains the most southerly coral reef in the world, in one of the most isolated ecosystems on the planet.</p>
<p>Following early reports of bleaching in the area, researchers from three Australian universities and two government agencies have worked together throughout March to investigate and document the bleaching.</p>
<p>Sustained heat stress has seen 90% of some reefs bleached, although other parts of the marine park have escaped largely unscathed. </p>
<h2>Bleaching is uneven</h2>
<p>Lord Howe Island was named a UNESCO World Heritage site in 1982. It is the coral reef closest to a pole, and contains many species found nowhere else in the world.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/266278/original/file-20190328-139341-160n3vh.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/266278/original/file-20190328-139341-160n3vh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/266278/original/file-20190328-139341-160n3vh.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/266278/original/file-20190328-139341-160n3vh.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/266278/original/file-20190328-139341-160n3vh.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/266278/original/file-20190328-139341-160n3vh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/266278/original/file-20190328-139341-160n3vh.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/266278/original/file-20190328-139341-160n3vh.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Coral bleaching observed at Lord Howe in March 2019.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Two of us (Tess Moriarty and Rosie Steinberg) have surveyed reefs across Lord Howe Island Marine Park to determine the extent of bleaching in the populations of hard coral, soft coral, and anemones. This research found severe bleaching on the inshore lagoon reefs, where up to 95% of corals are showing signs of extensive bleaching.</p>
<p>However, bleaching is highly variable across Lord Howe Island. Some areas within the Lord Howe Island lagoon coral reef are not showing signs of bleaching and have remained healthy and vibrant throughout the summer. There are also corals on the outer reef and at deeper reef sites that have remained healthy, with minimal or no bleaching.</p>
<p>One surveyed reef location in Lord Howe Island Marine Park is severely impacted, with more than 90% of corals bleached; at the next most affected reef site roughly 50% of corals are bleached, and the remaining sites are less than 30% bleached. At least three sites have less than 5% bleached corals. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/266279/original/file-20190328-139356-z3u5tj.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/266279/original/file-20190328-139356-z3u5tj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/266279/original/file-20190328-139356-z3u5tj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=413&fit=crop&dpr=1 600w, https://images.theconversation.com/files/266279/original/file-20190328-139356-z3u5tj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=413&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/266279/original/file-20190328-139356-z3u5tj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=413&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/266279/original/file-20190328-139356-z3u5tj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=519&fit=crop&dpr=1 754w, https://images.theconversation.com/files/266279/original/file-20190328-139356-z3u5tj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=519&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/266279/original/file-20190328-139356-z3u5tj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=519&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Healthy coral photographed at Lord Howe marine park in March 2019.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Over the past week heat stress has continued in this area, and return visits to these sites revealed that the coral condition has worsened. There is evidence that some corals are now dying on the most severely affected reefs. </p>
<p>Forecasts for the coming week indicate that water temperatures are likely to cool below the bleaching threshold, which will hopefully provide timely relief for corals in this valuable reef ecosystem. In the coming days, weeks and months we will continue to monitor the affected reefs and determine the impact of this event to the reef system, and investigate coral recovery.</p>
<h2>What’s causing the bleaching?</h2>
<p>The bleaching was caused by high seawater temperature from a persistent <a href="https://coralreefwatch.noaa.gov/data/5km/v3.1/image/daily/max_r07d_baa/gif/2019/coraltemp5km_max_r07d_baa_20190325_ese.gif">summer marine heatwave</a> off southeastern Australia. Temperature in January was a <a href="https://coralreefwatch.noaa.gov/data/5km/v3.1/image/composite/monthly/gif/2019/01/coraltemp5km_ssta_mean_201901_ese.gif">full degree Celsius warmer than usual</a>, and from the end of January to mid-February temperatures remained above the local bleaching threshold. </p>
<p>Sustained heat stressed the Lord Howe Island reefs, and put them at risk. They had a temporary reprieve with cooler temperatures in late February, but by March another increase put the ocean temperature well above safe levels. This is now the <a href="https://link.springer.com/article/10.1007/s00338-011-0778-7">third recorded bleaching event</a> to have occurred on this remote reef system.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/266438/original/file-20190328-139380-gd8q7g.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/266438/original/file-20190328-139380-gd8q7g.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/266438/original/file-20190328-139380-gd8q7g.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/266438/original/file-20190328-139380-gd8q7g.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/266438/original/file-20190328-139380-gd8q7g.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/266438/original/file-20190328-139380-gd8q7g.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/266438/original/file-20190328-139380-gd8q7g.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/266438/original/file-20190328-139380-gd8q7g.png?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">Satellite monitoring of sea-surface temperature (SST) revealed three periods in excess of the Bleaching Threshold during which heat stress accumulated (measured as Degree Heating Weeks, DHW). Since January 2019, SST (purple) exceeded expected monthly average values (blue +) by as much as 2°C. The grey line and envelope indicate the predicted range of SST in the near future.</span>
<span class="attribution"><span class="source">Source: NOAA Coral Reef Watch</span></span>
</figcaption>
</figure>
<p>However, this heatwave has not equally affected the whole reef system. In parts of the lagoon areas the water can be cooler, due to factors like ocean currents and fresh groundwater intrusion, protecting some areas from bleaching. Some coral varieties are also more heat-resistant, and a particular reef that has been exposed to high temperatures in the past may better cope with the current conditions. For a complex variety of reasons, the bleaching is unevenly affecting the whole marine park.</p>
<p>Coral bleaching is the greatest threat to the sustainability of coral reefs worldwide and is now clearly one of the greatest challenges we face in responding to the impact of global climate change. UNESCO World Heritage regions, such as the Lord Howe Island Group, require urgent action to address the cause and impact of a changing climate, coupled with continued management to ensure these systems remain intact for future generations.</p>
<p><br></p>
<hr>
<p><em>The authors thank ProDive Lord Howe Island and Lord Howe Island Environmental Tours for assistance during fieldwork.</em></p><img src="https://counter.theconversation.com/content/114433/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tess Moriarty received a scholarship from Women Diver's Hall of Fame - Marine Conservation Scholarship.</span></em></p><p class="fine-print"><em><span>Bill Leggat receives funding from the Australian Research Council and the Great Barrier Reef Foundation. </span></em></p><p class="fine-print"><em><span>C. Mark Eakin is employed and funded by the U.S. National Oceanic and Atmospheric Administration. The scientific results and conclusions, as well as any views or opinions expressed herein, are those of the author(s) and do not necessarily reflect the views of NOAA or the Department of Commerce.</span></em></p><p class="fine-print"><em><span>Scott Heron receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Tracy Ainsworth receives funding from The Australian Research Council and the Australian Academy of Science.</span></em></p><p class="fine-print"><em><span>Rosie Steinberg 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>Marine heatwaves have caused coral bleaching in one of the most isolated ecosystems in the world.Tess Moriarty, Phd candidate, University of NewcastleBill Leggat, Associate professor, University of NewcastleC. Mark Eakin, Coordinator, Coral Reef Watch, National Oceanic and Atmospheric AdministrationRosie Steinberg, PhD Student, UNSW SydneyScott F. Heron, Senior Lecturer, James Cook UniversityTracy Ainsworth, Associate professor, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1035822018-10-03T10:34:19Z2018-10-03T10:34:19ZFishing forecasts can predict marine creature movements<figure><img src="https://images.theconversation.com/files/237360/original/file-20180920-129856-1ldga9e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Swordfish only -- no bycatch, please.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/catching-swordfish-464482394?src=oqx2NcfMAugKGqxoCJTCKg-1-9">Joe Fish Flynn/shutterstock</a></span></figcaption></figure><p>Do you check the weather forecast before getting dressed in the morning? </p>
<p>If you do, then you’re making a decision in real time, based on dynamic processes that can vary greatly over space and time. Marine animals can be similarly dynamic. They might move in response to constantly shifting ocean conditions, like currents and fronts. </p>
<p>That led us to wonder: Can we predict marine wildlife like meteorologists predict the weather, so fisherman can make real-time decisions on the water? <a href="https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2664.13281">Our team</a> has been studying established tools like those used for weather forecasts, so we can <a href="http://advances.sciencemag.org/content/4/5/eaar3001">develop a new program</a> that estimates where marine species are likely to be each day. Unlike a weather forecast, our tool can’t help you decide if you need an umbrella or sunglasses, but it can help fishermen decide where to fish. </p>
<p>Our new application, called <a href="https://coastwatch.pfeg.noaa.gov/ecocast/">EcoCast</a>, launched late in 2017. It was created specifically for swordfish fisherman on the U.S. West Coast, so they can avoid protected species like leatherback turtles and California sea lions, often referred to as “bycatch.” These predictions are designed to help fishermen figure out where they are most likely to find the species they want to catch and least likely to find the species they want to avoid. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/237218/original/file-20180919-146148-1rbuvhu.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/237218/original/file-20180919-146148-1rbuvhu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/237218/original/file-20180919-146148-1rbuvhu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=970&fit=crop&dpr=1 600w, https://images.theconversation.com/files/237218/original/file-20180919-146148-1rbuvhu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=970&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/237218/original/file-20180919-146148-1rbuvhu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=970&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/237218/original/file-20180919-146148-1rbuvhu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1219&fit=crop&dpr=1 754w, https://images.theconversation.com/files/237218/original/file-20180919-146148-1rbuvhu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1219&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/237218/original/file-20180919-146148-1rbuvhu.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1219&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 EcoCast map from Sept. 5, 2018, showing waters that are better and poorer to fish.</span>
<span class="attribution"><span class="source">Elliott Hazen/NOAA</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Making predictions</h2>
<p>To create the EcoCast tool, we studied examples of established tools that make real-time predictions, such as <a href="https://www.wpc.ncep.noaa.gov/national_forecast/natfcst.php">weather forecasts</a>, <a href="https://www.nhc.noaa.gov/cyclones/">hurricane outlooks</a> and <a href="https://fsapps.nwcg.gov">wildfire incident alerts</a>.</p>
<p>We found that these tools all follow a similar workflow. First, they acquire data on current environmental conditions. For example, the National Hurricane Center <a href="http://www.hurricanescience.org/science/observation/aircraftrecon/">flies airplanes</a> through storm systems to acquire data on hurricane characteristics. The U.S. Forest Service accesses <a href="https://fsapps.nwcg.gov/afm/imagery_viirs.php?op=fire&passID=357071">new imagery</a> from satellite-borne sensors to observe fires from space. </p>
<p>Then, these tools predict their target features based on this new data. For example, the National Hurricane Center predicts hurricane location, intensity and movement. These predictions are then distributed to the public – perhaps through <a href="https://www.nhc.noaa.gov/aboutrss.shtml">RSS feeds</a>, texts or <a href="http://www.nws.noaa.gov/nwr/">radio alerts</a>. Finally, these predictions are automated. For example, the National Hurricane Center and the U.S. Forest Service create new hurricane and wildfire predictions every six hours. The National Weather Service creates daily forecasts.</p>
<p>We designed EcoCast to follow the same workflow. Each day, current satellite data such as <a href="https://worldview.earthdata.nasa.gov/?p=geographic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_L3_SST_MidIR_9km_Night_Annual,Reference_Labels(hidden),Reference_Features(hidden),Coastlines&t=2014-09-12-T00%3A00%3A00Z&z=3&v=-165.05130904650858,15.026129105967065,-91.14793326033433,53.632370188296896&ab=off&as=2014-09-05T00%3A00%3A00Z&ae=2014-09-12T00%3A00%3A00Z&av=3&al=false">sea surface temperature</a>, <a href="https://worldview.earthdata.nasa.gov/?p=geographic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_Chlorophyll_A,MODIS_Terra_L3_SST_MidIR_9km_Night_Annual(hidden),Reference_Labels(hidden),Reference_Features(hidden),Coastlines&t=2014-09-12-T00%3A00%3A00Z&z=3&v=-151.87398783727502,21.517488815578925,-103.11594334593559,46.988109072248776&ab=off&as=2014-09-05T00%3A00%3A00Z&ae=2014-09-12T00%3A00%3A00Z&av=3&al=true">chlorophyll concentration</a> and <a href="https://portal.aoos.org/#virtual-sensor/fb022313-1bd4-46c1-972b-622302122157/null,null,0,2018-09-12T00:00:00Z">sea surface height</a> are acquired from online repositories. This data helps us understand current oceanic conditions. </p>
<p>Then, we use mathematical models to predict the distributions of swordfish, turtles, sea lions and sharks. The models are tuned to each species’ environmental preferences. When we combine these models with data on current oceanic conditions, we can predict where species are most likely to be in real time. When we <a href="https://ashokharnal.wordpress.com/2014/03/14/a-very-simple-explanation-for-auc-or-area-under-the-roc-curve/">tested</a> the models, we found they <a href="http://advances.sciencemag.org/content/advances/suppl/2018/05/24/4.5.eaar3001.DC1/aar3001_SM.pdf">performed well</a> in distinguishing between where species were or were not located. </p>
<p>Next, we overlay the predicted species distributions to determine the ratio of swordfish, the target species, to the bycatch species – turtles, sea lions and sharks – in roughly 25 by 25 kilometer blocks. This map, <a href="https://coastwatch.pfeg.noaa.gov/ecocast/ecocast_efi.html">available online</a>, helps fishermen locate areas that are optimal for finding swordfish while avoiding bycatch species. For consistency, we scale each day’s map between 1 and negative 1, where areas valued closer to 1 are better to fish and negative 1 are poorer to fish. We automated the EcoCast tool to run every morning in order to produce a new map each day.</p>
<figure>
<iframe src="https://heatherwelch.shinyapps.io/ecocastapp/" height="500px" width="100%"></iframe>
<figcaption>An interactive web application to explore EcoCast predictions. <a href="https://coastwatch.pfeg.noaa.gov/ecocast/explorer.html">Developed by Heather Welch.</a></figcaption>
</figure>
<h2>Looking forward</h2>
<p>Thanks to increasing technological capacity and data availability, there are many <a href="https://ecoforecast.org/member-forecasting-profiles/">predictive tools under development</a> to help guide marine decisions. </p>
<p>For example, an international group of researchers is currently developing <a href="http://www.donahuelab.com/projects/fore-c/">FORE-C</a>, a coral disease outbreak forecasting tool for the western tropical Pacific Ocean. A tool called <a href="http://www.westcoast.fisheries.noaa.gov/whalewatch/">WhaleWatch</a> is being updated and expanded to help commercial vessels slow down or alter their shipping routes to avoid blue whale strikes offshore California. <a href="http://modata.ceoe.udel.edu/stur_prediction/cur_stur_model_fu1day.cat_flyer.png">Another tool</a> was recently launched to address the bycatch of Atlantic sturgeon in the Delaware Bay. </p>
<p>Predictive tools can be applied in situations with limited data, too. For example, another tool is under development by NOAA and an interdisciplinary group of researchers to guide the timing of a fishery closure in Southern California, designed to avoid bycatch of loggerhead turtles. </p>
<p>These tools reflect how digital technologies can improve marine management and conservation by integrating existing data. That’s crucial for helping stakeholders to make decisions about an ever-changing world.</p><img src="https://counter.theconversation.com/content/103582/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Heather Welch has received funding from National Oceanic and Atmospheric Administration, and the National Aeronautic and Space Administration. </span></em></p><p class="fine-print"><em><span>Elliott Hazen has received funding from the National Oceanic and Atmospheric Administration, the National Aeronautic and Space Administration, and California Seagrant for this work. </span></em></p><p class="fine-print"><em><span>Stephanie Brodie has received funding from the National Oceanic and Atmospheric Administration, the National Aeronautic and Space Administration, and California Seagrant for this work.</span></em></p>A new tool called EcoCast helps fishermen in the West Coast figure out where it’s best to fish that day.Heather Welch, Researcher in Ecosystem Dynamics, University of California, Santa CruzElliott Lee Hazen, Research Ecologist, National Oceanic and Atmospheric AdministrationStephanie Brodie, Project Scientist, University of California, Santa CruzLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/888052018-01-29T13:48:41Z2018-01-29T13:48:41ZHow open data can help the world better manage coral reefs<figure><img src="https://images.theconversation.com/files/202433/original/file-20180118-158550-1q8cd1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Coral reefs are some of the most diverse ecosystems in the world</span> <span class="attribution"><span class="source">NOAA Fisheries</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Coral reefs are critically important to the world but despite the ongoing efforts of scientists and campaigners, these stunningly beautiful ecosystems still face a <a href="https://theconversation.com/blue-planet-ii-can-we-really-halt-the-coral-reef-catastrophe-87286">variety of threats</a>. The most pervasive is, of course, climate change, which is putting their very future <a href="https://www.nature.com/articles/nature21707">in jeopardy</a>. </p>
<p>Climate change is a complex, worldwide problem that needs <a href="https://theconversation.com/curbing-climate-change-why-its-so-hard-to-act-in-time-80117">a global solution</a>. One part of which is good monitoring systems, that operate at a large scale. Broad scale datasets from these systems are required to understand how vulnerable ecosystems like coral reefs are changing, and to separate that information from natural variation. </p>
<p>Often, however, scientists that collect coral reef monitoring data do so in isolation. They work on independent research projects, or for relatively small programmes with specific local agenda, and so don’t always make their data available to the scientific community. The pressure on academic researchers to be the first to publish their findings also disincentives data sharing. So there can be a conflict of interest between the motivations of an individual scientist and the larger advancement of science. </p>
<p>More practically, getting data ready to share is time consuming, particularly when there aren’t standardised monitoring procedures or a good data management infrastructure in place. In the absence of good management, data can simply be lost as people move on, taking lab books, data sheets and external hard drives with them.</p>
<p>But these barriers can be overcome. Through, for example, open access journals that publish scientifically valuable datasets. Peer-reviewed, citable datasets with standardised meta-data promotes sharing and reusability, while also recognising the researchers behind it. </p>
<p>Given the now urgent need to find science-based solutions for coral reefs, we believe the benefits of open data far outweigh the costs. This is one of the reasons we recently published <a href="https://www.nature.com/articles/sdata2017176">our entire dataset</a> of coral reef habitats and fish assemblages in the western central Pacific. </p>
<figure>
<iframe src="https://player.vimeo.com/video/250585106" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">Counting fish at Jarvis Island, one of the most remote coral reefs on the planet (Kevin Lino/NOAA Fisheres)</span></figcaption>
</figure>
<h2>Pooling data</h2>
<p>Our dataset was collected by scientific divers from the US national oceanic and atmospheric administration between 2010 and 2017. They were part of the interdisciplinary team that operates from NOAA ships to collect physical, chemical and biological data for the <a href="https://www.pifsc.noaa.gov/cred/pacific_ramp.php">pacific reef assessment and monitoring programme</a>. For seven years, these researchers surveyed fish assemblages and coral reef habitats at 39 islands and atolls in the United States affiliated western central Pacific. </p>
<p>The areas studied ranged from the remotest islands in the central Pacific – hundreds of kilometres from the nearest human civilisations – to highly populated, developed and urbanised islands such as Oahu and Guam. </p>
<p>These islands also have different biophysical conditions, such as temperature. This means that we have been able to quantify different threats relative to the natural background variability caused by environmental conditions. For instance, we can now understand the true effect of human depletion <a href="https://theconversation.com/measuring-coral-reef-fishes-by-taking-humans-out-of-the-picture-40213">on coral reef fishes</a>. We have also been able to set reasonable expectations for what <a href="https://theconversation.com/coral-reefs-physical-conditions-set-biological-rules-of-nature-until-people-show-up-37688">a healthy reef looks like</a> in different locations. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/202442/original/file-20180118-158522-7oxfln.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/202442/original/file-20180118-158522-7oxfln.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/202442/original/file-20180118-158522-7oxfln.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=568&fit=crop&dpr=1 600w, https://images.theconversation.com/files/202442/original/file-20180118-158522-7oxfln.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=568&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/202442/original/file-20180118-158522-7oxfln.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=568&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/202442/original/file-20180118-158522-7oxfln.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=713&fit=crop&dpr=1 754w, https://images.theconversation.com/files/202442/original/file-20180118-158522-7oxfln.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=713&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/202442/original/file-20180118-158522-7oxfln.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=713&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 areas studied by the NOAA divers.</span>
<span class="attribution"><span class="source">NOAA Fisheries</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>When multiple large data sets like this are pooled, they become even more powerful, allowing researchers to tackle key questions, such as where coral reef “<a href="https://theconversation.com/there-are-bright-spots-among-the-worlds-coral-reefs-the-challenge-is-to-learn-from-them-62765">bright spots</a>” are and why they are thriving.</p>
<h2>Scientific advancements</h2>
<p>By making all data easily available like ours is, and working to improve comparability, we can speed up the scientific pace to better understand and manage coral reefs. Though we were required to make the NOAA data available under the <a href="https://opengovdata.io/2014/us-federal-open-data-policy/">United States Open Data Policy</a>, we believe it is important for the wider coral reef community to fully embrace this ideal. Coral reefs are so widespread that no one programme can hope to gather data across most of their range. <a href="https://jappliedecologyblog.wordpress.com/2016/03/30/jazz-band-ecosystem-monitoring/">Linking large and small-scale programmes</a> will improve the value of both: large datasets can give the big picture context, while <a href="https://theconversation.com/a-local-view-helps-fight-the-effects-of-climate-change-on-the-ocean-70180">localised programmes</a> can be more intensive or regularly repeated.</p>
<p>One <a href="https://www.nature.com/articles/nature14358">landmark study</a>, for example – which used open datasets from different sources – found that the majority of coral reefs are fished to under half of their maximum population. So a range of management target benchmarks were established. Another compiled 25 different datasets to report on the status of coral reef fish biomass at 37 different districts <a href="http://onlinelibrary.wiley.com/doi/10.1002/aqc.2832/abstract">in Hawaii</a>, covering almost the entire archipelago’s coastline. Not only does this collated data help local reef management, but it can be used for marine spatial planning and for assessing effectiveness of reef management elsewhere. </p>
<p>There are a certainly a number of challenges to bringing different datasets together. Scientists will have to work together to create a core set of community standards for how to calibrate across different methods, and what to monitor. But by doing this, the information we gather will be far more useful in addressing the coral reef crisis. A commitment to open data is an important part of this.</p><img src="https://counter.theconversation.com/content/88805/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adel Heenan received funding from the NOAA coral reef conservation programme. </span></em></p><p class="fine-print"><em><span>Ivor D. Williams receives funding from the NOAA coral reef conservation programme.</span></em></p>If researchers shared their data, we could take a big step towards saving the world’s coral reefs.Adel Heenan, Postdoctoral fellow, Bangor UniversityIvor D. Williams, Coral Reef Ecologist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/840812017-10-02T19:16:18Z2017-10-02T19:16:18ZQuand les anchois confondent le plastique avec un bon repas<figure><img src="https://images.theconversation.com/files/186599/original/file-20170919-22705-4s1x9m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Sculpture réalisée à base d'éléments en plastique, à Helsingør, Hovedstaden au Danemark. Malene Møh</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/hepp/16204517281/in/photolist-qFWoqZ-9Dy8Hy-SobeN2-SJfVnx-bJEh6e-a5FMNo-9xzBCj-2ZU3mW-TC4BTP-5MvCK2-7FyTcq-86dTQY-byr41o-6Qim4z-Sni3x-91ekq7-4SsD7B-dqyiZJ-5p5Pky-6nyqK-9HDk2Y-7HM52f-XSGyBj-5VT8Sy-kx4FXe-fV38BU-RD9qWC-WF28VL-7FuUpx-pPMAPE-9LFwn4-StzgqV-4TgsNr-4uCEmm-9AfiYR-9Afi12-bbACyz-7Fv75x-7jqyJQ-bK53s2-RoAp9B-7ppJ4P-a42Azr-59Z48q-4Bq4g2-8WZwTp-92fH6p-8NoNpX-SkueXd-Uhwvzw">erik forsberg/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Au moment de savourer un délicieux poisson vous pensez rarement à ce que lui a pu manger. Mais peut-être devriez-vous… La recherche a montré que plus de cinquante espèces de poissons consomment du plastique dans la mer. Ce n’est pas seulement une mauvaise nouvelle pour eux, mais également pour les populations qui comptent sur le poisson pour subvenir à leurs besoins alimentaires.</p>
<p>En général, les poissons ne meurent pas de l’ingestion d’un fragment de l’<a href="http://www.ready-for-the-resource-revolution.com/en/marine-plastic-debris-and-microplastics-a-new-unep-report-on-plastic-pollution-in-our-oceans">énorme quantité de plastique flottant dans les océans</a>. Cela dit, ce n’est pas sans danger pour eux : <a href="http://dx.doi.org/10.1021/es5053655">leur activité est modifiée et leur comportement social change</a>. Au niveau physiologique, leur <a href="http://dx.doi.org/10.1038/srep03263">fonction hépatique est en berne</a>.</p>
<p>Ce qui pourrait être plus problématique pour nous, c’est que certains composés toxiques comme les <a href="https://oceanservice.noaa.gov/facts/pbde.html">PBDEs</a> (Polybromodiphényléther), associés aux plastiques traversent les tissus des poissons et s’y accumulent. Cette découverte signifie que ces mêmes substances pourraient également être stockées à l’intérieur de nos corps. L’estomac de plusieurs espèces de consommation courante comme le maquereau, le bar rayé et les huîtres du Pacifique contiennent du plastique.</p>
<p>Il est bien connu que nos déchets plastiques font peser une <a href="http://dx.doi.org/10.1073/pnas.1502108112">lourde menace</a> sur les animaux marins mais nous essayons toujours de comprendre pourquoi ils en mangent. Des recherches ont conclu que les animaux confondent, visuellement, plastique et nourriture.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ieMXDlMP0b8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Les tortues de mer peuvent se laisser mourir de faim parce qu’elles ont l’impression d’être rassasiées après avoir ingéré des sacs plastiques ou d’autres débris.</span></figcaption>
</figure>
<p>Cela pourrait être vrai mais une telle information ne serait qu’une partie d’un tableau plus large. Dans une étude récente réalisée avec nos collègues de l’université de Californie, nous avons montré que les débris de plastique auraient également une <a href="http://advances.sciencemag.org/content/2/11/e1600395">odeur attractive pour les organismes marins</a>. Cette étude se focalise sur les oiseaux de mer, mais mes co-auteurs et moi-même avons trouvé que les déchets plastiques avaient <a href="http://rspb.royalsocietypublishing.org/content/284/1860/20171000">des effets similaires sur les anchois</a>, une espèce majeure dans les chaînes alimentaires des océans.</p>
<h2>Flairer le rôle des odeurs</h2>
<p>Le sens de l’olfaction est extrêmement important pour la faune marine et donc pour les poissons. Les requins peuvent sentir des quantités infinitésimales de sang à de <a href="http://www.amnh.org/learn/pd/sharks_rays/rfl_myth/myth_page5.html">très grandes distances</a>, ce qui leur permet de chasser. Les scientifiques pensent que l’odorat du saumon les aide à <a href="https://www.sciencedaily.com/releases/2013/02/130207131713.htm">remonter les rivières</a> vers les affluents spécifiques qui les ont vus naître pour y pondre à leur tour. Les poissons peuvent utiliser ce sens dans des contextes comportementaux comme l’accouplement, le choix de leur lieu de vie, leur migration et leur recherche de nourriture.</p>
<p>Nous avons testé l’hypothèse suivante : est-ce que les <a href="http://rspb.royalsocietypublishing.org/content/284/1860/20171000">débris plastiques sentent bon</a> pour les <a href="http://wdfw.wa.gov/fishing/forage_fish/northern_anchovy.html">anchois du pacifique</a> (<em>Engraulis mordax</em>) ? Cette espèce vit en bancs proche de la côte ouest d’Amérique du Nord. Les anchois sont une espèce d’une importance écologique et économique majeure. Malheureusement, ils se nourrissent également de <a href="http://dx.doi.org/10.1038/srep34351">plastique dans la nature</a>.</p>
<p>Travailler avec des anchois n’est pas chose aisée dans la mesure où ils ont besoin de conditions hydrologiques mais aussi de taille de bancs spécifiques pour se comporter naturellement. Ils doivent être dans de l’eau froide avec un courant fort et dans des bancs d’au moins cent individus. Quand toutes ces conditions sont réunies, ils montrent leur satisfaction en nageant lentement et dans le sens du flux de l’eau – ce comportement s’appelle la rhéotaxie positive. Par chance, nous collaborons avec l’<a href="https://www.aquariumofthebay.org">Aquarium de San Francisco</a>, expert dans l’art de maintenir leurs poissons heureux et en bonne santé.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.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">Bancs d’anchois du Pacifique.</span>
<span class="attribution"><span class="source">Matthew Savoca</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Expérience olfactive</h2>
<p>Au moment de démarrer l’expérience, nous ne savions pas si les anchois adultes utilisaient leur odorat pour trouver de la nourriture et donc encore moins si une odeur allait les pousser à manger du plastique. Afin de tester notre hypothèse, nous avons fait tremper du krill (de petits crustacés ressemblant à des crevettes dont se nourrissent les anchois) ou des débris de plastique ou du plastique propre dans de l’eau de mer pendant plusieurs heures. Ceci a permis à l’eau de se charger en odeurs. Nous avons ensuite filtré le krill ou le plastique puis avons versé cette eau aux bancs d’anchois pour observer leur comportement.</p>
<p>Quand les anchois recherchent de la nourriture en groupe, leur comportement est relativement prédictible : ils se groupent et se précipitent vers le stimulus intéressant, changeant la position de leur corps par rapport au courant de l’eau. Pour comparer comment les anchois allaient répondre aux senteurs de krill ou de plastique, nous avons fait pendre au-dessus de l’aquarium un appareil spécialement conçu pour cette expérience, attaché à une caméra GoPro pour filmer le comportement du banc vu d’au-dessus.</p>
<p>De plus, pour analyser ce que les anchois faisaient lorsqu’ils détectaient des odeurs, nous avons également filmé leur comportement quand ils se nourrissent de krill et lorsqu’ils sont en présence de traitements contrôle ou de l’eau de mer « sans odeur ». Cela nous a donné une ligne de base à propos de leur comportement en bancs que nous avons pu comparer aux réponses obtenus à nos différents tests.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.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">Banc d’anchois avant exposition aux plastiques.</span>
<span class="attribution"><span class="source">Matthew Savoca</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>En utilisant une combinaison d’analyses informatiques et d’observations, nous avons évalué à quel point les poissons étaient proches les uns des autres et comment le corps de chaque poisson se positionnait par rapport au sens du courant, avant et après avoir ajouté une odeur dans l’aquarium. Comme nous l’avions prédit, quand les poissons étaient nourris, les bancs devenaient plus denses, ils changeaient également la position de leur corps de façon à ce que tous les poissons fassent face au courant, leurs corps s’alignaient de façon désordonnée quand ils cherchaient des morceaux de nourriture. Dans les traitements contrôles, sans nourriture et sans odeur, nous n’avons pas observé ces changements.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.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">Les mêmes anchois après avoir été exposés à l’odeur de plastique.</span>
<span class="attribution"><span class="source">Matthew Savoca</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Quand nous avons injecté de l’eau de mer à l’odeur de krill dans l’aquarium, les anchois ont répondu comme s’ils étaient en train de chercher de la nourriture – qui, dans ce cas, n’était pas là. Quand nous leur avons présenté de l’eau de mer à l’odeur de détritus de plastique, les bancs ont répondu presque de la même manière, se rapprochant les uns des autres et bougeant de façon aléatoire comme s’ils recherchaient de la nourriture. Cette réaction est la première preuve comportementale qu’un vertébré marin puisse être poussé à consommer du plastique à cause de son odeur.</p>
<h2>Réduire la pollution plastique</h2>
<p>Cette recherche confirme plusieurs choses. Premièrement les anchois du Pacifique Nord utilisent les odeurs pour localiser la nourriture. Cela peut paraître intuitif, mais avant notre étude il n’était pas prouvé que les <a href="https://fr.wikipedia.org/wiki/Poisson_fourrage">poissons de fourrage</a> comme les anchois, les sardines ou les harengs utilisaient leur odorat pour trouver de la nourriture.</p>
<p>Notre découverte principale a été que les débris plastiques sont perturbants pour ces consommateurs marins à cause de leurs apparences et de leurs odeurs. C’est un problème parce que si le plastique a l’air et sent bon pour le poisson, ce sera très difficile pour eux de discerner que ce n’est pas de la nourriture.</p>
<p>Cette étude suggère également que notre culture du « consommer et jeter » nous rattrape lorsque nous mangeons du poisson. La prochaine question importante que cela pose est de savoir si ces contaminants dérivés du plastique peuvent se transférer des poissons mangeurs de plastiques aux humains mangeurs de poissons.</p>
<p>Une façon de se centrer sur le problème est de comprendre pourquoi les animaux confondent plastique et proie si fréquemment, et en ce sens, notre étude a aidé. Cependant, tout le monde peut faire quelque chose contre la pollution des océans en évitant des objets en plastique jetable et en recyclant le plastique. Nous en savons suffisamment maintenant pour pouvoir s’attaquer à ce problème planétaire.</p><img src="https://counter.theconversation.com/content/84081/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Savoca a été financé par la National Science Foundation et le California Sea Grant.</span></em></p>La mer de plastique dans laquelle nagent les poissons n’est pas seulement une catastrophe écologique. Elle met en danger des espèces comme les anchois qui prennent ces débris pour de la nourriture.Matthew Savoca, Postdoctoral fellow, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/848422017-10-02T18:40:34Z2017-10-02T18:40:34ZHow to work out which coral reefs will bleach, and which might be spared<p>Regional variations in sea surface temperature, related to seasons and El Niño, could be crucial for the survival of coral reefs, according to our <a href="http://nature.com/articles/doi:10.1038/nclimate3399">new research</a>. This suggests that we should be able to identify the reefs most at risk of mass bleaching, and those that are more likely to survive unscathed.</p>
<p>Healthy coral reefs support diverse ecosystems, hosting <a href="http://www.reefresilience.org/coral-reefs/reefs-and-resilience/value-of-reefs/">25% of all marine fish species</a>. They provide food, coastal protection and <a href="http://www.reefresilience.org/coral-reefs/reefs-and-resilience/value-of-reefs/">livelihoods for at least 500 million people</a>.</p>
<p>But global warming, coupled with other pressures such as nutrient and sediment input, changes in sea level, waves, storms, ventilation, hydrodynamics, and ocean acidification, could lead to the <a href="http://e360.yale.edu/features/is_the_end_in_sight_for_the_worlds_coral_reefs">end of the world’s coral reefs in a couple of decades</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-much-coral-has-died-in-the-great-barrier-reefs-worst-bleaching-event-69494">How much coral has died in the Great Barrier Reef's worst bleaching event?</a>
</strong>
</em>
</p>
<hr>
<p>Climate warming is the major cause of stress for corals. The world just witnessed an event described as the “<a href="https://coralreefwatch.noaa.gov/satellite/analyses_guidance/global_coral_bleaching_2014-17_status.php">longest global coral die-off on record</a>”, and scientists have been raising the alarm about coral bleaching for decades. </p>
<p>The first global-scale mass bleaching event happened in 1998, destroying <a href="http://www.reefbase.org/resource_center/publication/statusreport.aspx?refid=27173">16% of the world coral reefs</a>. Unless greenhouse emissions are drastically reduced, the question is no longer if coral bleaching will happen again, but when and how often?</p>
<p>To help protect coral reefs and their ecosystems, effective management and conservation strategies are crucial. Our research shows that understanding the relationship between natural variations of sea temperature and human-driven ocean warming will help us identify the areas that are most at risk, and also those that are best placed to provide safe haven.</p>
<h2>A recurrent threat</h2>
<p>Bleaching happens when sea temperatures are unusually high, causing the corals to expel the coloured algae that live within their tissues. Without these algae, corals are unable to reproduce or to build their skeletons properly, and can ultimately die.</p>
<p>The two most devastating global mass bleaching events on record – in 1998 and <a href="https://theconversation.com/au/topics/2016-coral-bleaching-event-26991">2016</a> – were both triggered by <a href="https://theconversation.com/australias-climate-in-2016-a-year-of-two-halves-as-el-nino-unwound-70758">El Niño</a>. But when water temperatures drop back to normal, corals can often recover.</p>
<p>Certain types of coral can also acclimatise to rising sea temperatures. But as our planet warms, periods of bleaching risk will become more frequent and more severe. As a consequence, corals will have less and less time to recover between bleaching events.</p>
<p>We are already witnessing a decline in coral reefs. Global populations have declined by <a href="http://www.reefbase.org/resource_center/publication/statusreport.aspx?refid=27173">1-2% per year</a> in response to repeated bleaching events. Closer to home, the Great Barrier Reef <a href="http://www.pnas.org/content/109/44/17995.full.pdf">lost 50% of its coral cover between 1985 and 2012</a>.</p>
<h2>A non-uniform response to warming</h2>
<p>While the future of worldwide coral reefs looks dim, not all reefs will be at risk of recurrent bleaching at the same time. In particular, reefs located south of 15ºS (including the Great Barrier Reef, as well as islands in south Polynesia and Melanesia) are likely to be the last regions to be affected by harmful recurrent bleaching.</p>
<p>We used to think that Micronesia’s reefs would be among the first to die off, because the climate is warming faster there than in many other places. But our research, <a href="http://nature.com/articles/doi:10.1038/nclimate3399">published today in Nature Climate Change</a>, shows that the overall increase in temperature is not the only factor that affects coral bleaching response. </p>
<p>In fact, the key determinant of recurrent bleaching is the natural variability of ocean temperature. Under warming, temperature variations associated with seasons and climate processes like El Niño influence the pace of recurrent bleaching, and explain why some reefs will experience bleaching risk sooner than others in the future.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/188294/original/file-20171002-28500-6tjhbm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/188294/original/file-20171002-28500-6tjhbm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/188294/original/file-20171002-28500-6tjhbm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/188294/original/file-20171002-28500-6tjhbm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/188294/original/file-20171002-28500-6tjhbm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/188294/original/file-20171002-28500-6tjhbm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/188294/original/file-20171002-28500-6tjhbm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/188294/original/file-20171002-28500-6tjhbm.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">Different zones of the Pacific are likely to experience differing amounts of climate variability.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/188290/original/file-20171002-28494-11s9zjp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/188290/original/file-20171002-28494-11s9zjp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/188290/original/file-20171002-28494-11s9zjp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=205&fit=crop&dpr=1 600w, https://images.theconversation.com/files/188290/original/file-20171002-28494-11s9zjp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=205&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/188290/original/file-20171002-28494-11s9zjp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=205&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/188290/original/file-20171002-28494-11s9zjp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=257&fit=crop&dpr=1 754w, https://images.theconversation.com/files/188290/original/file-20171002-28494-11s9zjp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=257&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/188290/original/file-20171002-28494-11s9zjp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=257&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Degrees of future bleaching risk for corals in the three main Pacific zones.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Our results suggest that El Niño events will continue to be the major drivers of mass bleaching events in the central Pacific. As average ocean temperatures rise, even mild El Niño events will have the potential to trigger widespread bleaching, meaning that these regions could face severe bleaching every three to five years within just a few decades. In contrast, only the strongest El Niño events will cause mass bleaching in the South Pacific. </p>
<p>In the future, the risk of recurrent bleaching will be more seasonally driven in the South Pacific. Once the global warming signal pushes summer temperatures to dangerously warm levels, the coral reefs will experience bleaching events every summers. In the western Pacific, the absence of natural variations of temperatures initially protects the coral reefs, but only a small warming increase can rapidly transition the coral reefs from a safe haven to a permanent bleaching situation.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/feeling-helpless-about-the-great-barrier-reef-heres-one-way-you-can-help-76014">Feeling helpless about the Great Barrier Reef? Here's one way you can help</a>
</strong>
</em>
</p>
<hr>
<p>One consequence is that, for future projections of coral bleaching risk, the global warming rate is important but the details of the regional warming are not so much. The absence of consensus about regional patterns of warming across climate models is therefore less of an obstacle than previously thought, because globally averaged warming provided by climate models combined with locally observed sea temperature variations will give us better projections anyway.</p>
<p>Understanding the regional differences can help reef managers identify the reef areas that are at high risk of recurring bleaching events, and which ones are potential temporary safe havens. This can buy us valuable time in the battle to protect the world’s corals.</p><img src="https://counter.theconversation.com/content/84842/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Clothilde Emilie Langlais was funded by the Pacific Australian Climate Science and Adaptation Program funded by AusAid.</span></em></p><p class="fine-print"><em><span>Scott Heron receives funding and support from the U.S. National Oceanic and Atmospheric Administration's Satellites division (NESDIS) and Coral Reef Conservation Program, and is affiliated with James Cook University. The contents in this piece are solely the opinions of the authors and do not constitute a statement of policy, decision or position on behalf of NOAA or the U.S. Government.</span></em></p><p class="fine-print"><em><span>Andrew Lenton 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>Regional variations in sea temperature can make all the difference between a coral reef suffering major bleaching or surviving as a refuge for corals, new research shows.Clothilde Emilie Langlais, research scientist at CSIRO Oceans and Atmosphere, CSIROAndrew Lenton, Senior Research Scientist, Oceans and Atmosphere, CSIROScott F. Heron, Physical Scientist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/816072017-08-16T01:37:27Z2017-08-16T01:37:27ZBait and switch: Anchovies eat plastic because it smells like prey<figure><img src="https://images.theconversation.com/files/181977/original/file-20170814-28423-i5knb3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Plastic trash on San Francisco's Ocean Beach.</span> <span class="attribution"><a class="source" href="https://flic.kr/p/7Hxy4a">Kevin Krejci</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>As you bite down into a delicious piece of fish, you probably don’t think about what the fish itself ate – but perhaps you should. Over 50 species of fish have been found to consume plastic trash at sea. This is bad news, not only for fish but potentially for humans who rely on fish for sustenance. </p>
<p>Fish don’t usually die as a direct result of feeding on the <a href="http://www.ready-for-the-resource-revolution.com/en/marine-plastic-debris-and-microplastics-a-new-unep-report-on-plastic-pollution-in-our-oceans/">enormous quantities of plastic trash</a> floating in the oceans. But that doesn’t mean it’s not harmful for them. Some negative effects that scientists have discovered when fish consume plastic include <a href="http://dx.doi.org/10.1021/es5053655">reduced activity rates and weakened schooling behavior</a>, as well as <a href="http://dx.doi.org/10.1038/srep03263">compromised liver function</a>. </p>
<p>Most distressingly for people, toxic compounds such as <a href="https://en.wikipedia.org/wiki/Polybrominated_diphenyl_ethers">PBDEs</a> that are associated with plastic transfer to and bioaccumulate in <a href="http://dx.doi.org/10.1021/acs.est.5b06280">fish tissues</a>. This finding is troubling because it means these toxic substances could further bioaccumulate in us if we consume fish that have eaten plastic. Numerous species sold for human consumption, including mackerel, striped bass and Pacific oysters <a href="http://dx.doi.org/10.1038/srep14340">have been found with these toxic plastics in their stomachs</a> too.</p>
<p>It is well-known that our plastic trash poses <a href="http://dx.doi.org/10.1073/pnas.1502108112">a serious threat</a> to marine animals, but we are still trying to understand why animals eat it. Typically, research has concluded that marine animals visually mistake plastic for food. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ieMXDlMP0b8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Sea turtles can starve to death because they feel full after swallowing plastic bags or other debris.</span></figcaption>
</figure>
<p>While this may be true, the full story is likely more complex. For example, in a recent study with colleagues at the University of California, Davis, we showed that <a href="http://advances.sciencemag.org/content/2/11/e1600395">plastic debris may also smell attractive to marine organisms</a>. That study focused on seabirds, but now my co-authors and I have found that plastic trash <a href="http://rspb.royalsocietypublishing.org/content/284/1860/20171000">has a similar effect on anchovies</a> – a critical part of ocean food chains.</p>
<h2>Sniffing out the role of smell</h2>
<p>Olfaction (smell) is a very important sense for marine animals, including fish. Sharks can smell minute quantities of blood <a href="http://www.amnh.org/learn/pd/sharks_rays/rfl_myth/myth_page5.html">over long distances</a>, which helps them find prey. And scientists believe that salmon’s sense of smell helps them <a href="https://www.sciencedaily.com/releases/2013/02/130207131713.htm">navigate up rivers</a> to the specific tributaries where they were born to spawn. Fish may use their sense of smell in behavioral contexts including mating, homing, migrating and foraging. </p>
<p>We tested the idea that <a href="http://rspb.royalsocietypublishing.org/content/284/1860/20171000">plastic debris might smell attractive</a> to the <a href="http://wdfw.wa.gov/fishing/forage_fish/northern_anchovy.html">Northern anchovy</a> (<em>Engraulis mordax</em>), a common schooling fish found off the West Coast of North America. Known as forage fish, anchovies are critically important species ecologically and economically. Unfortunately, they have also been found to <a href="http://dx.doi.org/10.1038/srep34351">eat plastic in the wild</a>. </p>
<p>Working with anchovies is challenging because they require very specific water conditions and school size to behave normally. They need to be in cold, fast-flowing water in schools of at least 100 individuals. When that happens, the anchovies display their contentment by swimming slowly and directly into the flow of water – a behavior known as positive rheotaxis. Luckily, we were able to collaborate with the <a href="https://www.aquariumofthebay.org/">Aquarium of the Bay</a> in San Francisco, where they have expertise in keeping these fish happy and healthy. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182105/original/file-20170815-5485-15exuec.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">Schooling Northern anchovies.</span>
<span class="attribution"><span class="source">Matthew Savoca</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Our olfactory experiment</h2>
<p>When we started the experiment we did not know whether adult anchovies used their sense of smell to find food at all, let alone whether smell might lead them to consume plastic. To test our hypothesis that it would, we soaked <a href="http://www.nationalgeographic.com/animals/invertebrates/group/krill/">krill</a> (tiny shrimp-like crustaceans that anchovies eat) or plastic debris and clean plastic in seawater for several hours, allowing the water to take on the smell of the material steeping in it. We then filtered our krill or plastic “tea,” presented it to the anchovy schools, and observed their behavior. </p>
<p>When fish are searching for food in groups, their behavior changes in predictable ways: They clump together near the interesting stimulus and dart around, altering their body position relative to the water current. To compare how anchovies responded to the scents of krill and plastic, we hung a specially designed apparatus with a GoPro camera attached over their tank to film the school’s behavior from above. </p>
<p>In addition to analyzing what anchovies did when they detected these odors, we also filmed their anchovies’ behavior while feeding on krill and when they were presented with control treatments of unscented seawater. This gave us baseline information about the schools’ behavior, which we could compare to their responses when they were presented with the different odors.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182000/original/file-20170814-14751-w61yev.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">Anchovies schooling in a tank before being exposed to the odor of plastic debris.</span>
<span class="attribution"><span class="source">Matthew Savoca</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Using a combination of automated computer analyses and diligent observer scoring, we evaluated how tightly the schools clumped together and how each fish’s body positioning relative to the direction of water flow changed before and after adding an odor solution to the tank. As we predicted, when the anchovies were feeding, schools became more densely clumped and changed their body positioning so that instead of all fish facing directly into the oncoming current, their bodies aligned more haphazardly as they searched for food morsels. In the control treatments, with no food or food odors present, we did not observe these changes. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182001/original/file-20170814-5720-1nwtbh3.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 same anchovies displaying feeding behavior after being exposed to the odor of plastic debris.</span>
<span class="attribution"><span class="source">Matthew Savoca</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>When we injected seawater scented with krill into the tank, the anchovies responded as if they were searching for food – which in this case was not there. And, importantly, when we presented them with seawater scented with odors of plastic debris, the schools responded in nearly the same way, clumping together and moving erratically as they would if they were searching for food. This reaction provided the first behavioral evidence that a marine vertebrate may be tricked into consuming plastic because of the way it smells.</p>
<h2>Reducing plastic pollution</h2>
<p>This research confirms several things. First, we showed that Northern anchovies use odors to locate food. This may sound intuitive, but before we did this study there was scant behavioral evidence that adult <a href="https://en.wikipedia.org/wiki/Forage_fish">forage fish</a>, such as anchovies, sardines and herring used smell to find food. </p>
<p>Our main finding was that plastic debris is likely confusing for marine consumers because of both its appearance and its smell. That’s a problem, because if plastic looks and smells interesting to fish, it will be very hard for them to discern that is it not food.</p>
<p>This study also suggests that our consume-and-dispose culture is coming back to haunt us via the fish we eat. The next big question that it raises is whether plastic-derived contaminants can be transferred from plastic-eating fish to fish-eating humans. </p>
<p>One way to mitigate the problem is to figure out why animals confuse plastic for prey so frequently, and our research has helped to do that. However, everyone can do something right now about ocean plastic pollution by avoiding single-use plastic items and recycling plastic upon disposal. There is more work to be done, but we know enough now to make substantial headway on this global environmental issue.</p><img src="https://counter.theconversation.com/content/81607/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Savoca receives funding from the National Science Foundation and California Sea Grant. </span></em></p>A new study shows that anchovies – key food for larger fish – are attracted to plastic trash because it smells like food. This suggests that toxic substances in plastic could move up through food chains.Matthew Savoca, Postdoctoral fellow, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/691952016-11-30T02:57:58Z2016-11-30T02:57:58ZUnderstanding the conditions that foster coral reefs’ caretaker fishes<figure><img src="https://images.theconversation.com/files/147032/original/image-20161122-10997-1cc4jrb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Whitespotted surgeonfish (_Acanthurus guttatus_), found in the Indo-Pacific, crop the upper portion of algae while feeding, preventing macroalgae from becoming established on reefs.</span> <span class="attribution"><a class="source" href="http://www.photolib.noaa.gov/htmls/corl0403.htm">Kevin Lino/NOAA</a></span></figcaption></figure><p>Coral reefs are among the most valuable natural assets on Earth. They provide an estimated <a href="http://oceanservice.noaa.gov/education/kits/corals/coral07_importance.html">US$375 billion worth of goods and services</a> every year, such as supporting fisheries and protecting coasts. But reefs face many <a href="https://theconversation.com/how-fish-and-clean-water-can-protect-coral-reefs-from-warming-oceans-60434">stresses and shocks</a>, from local threats like overfishing, habitat damage and pollution to the <a href="https://theconversation.com/as-the-earth-enters-its-third-mass-bleaching-event-will-corals-survive-50740">global impacts of climate change</a>. Many scientists are working to identify management strategies that can effectively buffer reefs against the array of threats that challenge them.</p>
<p>Herbivorous fish (species that eat plants) are critical for healthy coral reefs because they help to regulate the constant competition for space between corals and seaweeds. Hard corals and other reef-building organisms form hard skeletons out of calcium carbonate, while fleshy organisms such as seaweeds and algal turfs (thick mats of short algae) grow on the surfaces of these hard structures. By feeding on seaweeds and algal turfs, herbivorous fish prevent these organisms from smothering reefs. </p>
<p><a href="https://www.iucn.org/content/status-and-trends-caribbean-coral-reefs-1970-2012">Recent studies</a> have stressed the importance for coral reef conservation of protecting herbivorous fish, which are heavily fished in many parts of the world. But in a <a href="http://dx.doi.org/10.1098/rspb.2016.1716">new study</a>, we found that populations of herbivorous fish vary widely from site to site, and are strongly influenced by factors including temperature and island type. This means that strategies to protect these important species may not work unless they take local conditions into account, and no single strategy is likely to work everywhere.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/146849/original/image-20161121-4524-svfhqy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/146849/original/image-20161121-4524-svfhqy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/146849/original/image-20161121-4524-svfhqy.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/146849/original/image-20161121-4524-svfhqy.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/146849/original/image-20161121-4524-svfhqy.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/146849/original/image-20161121-4524-svfhqy.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/146849/original/image-20161121-4524-svfhqy.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 coral-dominated reef, with algae held in check.</span>
<span class="attribution"><span class="source">Brian J. Zgliczynski (Scripps Institution of Oceanography)</span></span>
</figcaption>
</figure>
<h2>Coral reef caretakers</h2>
<p>Fishing has caused <a href="http://dx.doi.org/10.1098/rspb.2013.1835">widespread reductions</a> in herbivorous fish populations on coral reefs around the world. Because fishing has had such pervasive global effects, it is hard to separate human impacts from the natural biophysical and environmental drivers of these fish populations. </p>
<p>But we need to make this distinction if we want to understand why herbivores might be naturally more prevalent in some places than others, and to measure true human-related depletion effects accurately. More specifically, in this study we wanted to know whether it was reasonable to expect the same amount of these fishes in areas where environmental conditions are very different.</p>
<p>All herbivorous fish are not equal. Depending on what they eat, they perform different roles that contribute to the functioning of coral reefs, much in the same way that lawn mowers and hedge trimmers perform different tasks in your garden. To understand how these fishes differ in their response to the environment, we classified fishes in our study based on their functional roles, defined by what they eat and how they eat it. </p>
<p>For example, browsers eat fleshy seaweeds; detritivores comb algal turfs, feeding on a variety of fine plant and animal matter; and scrapers and excavators scrape hard surfaces on the reef, clearing space for corals to colonize. Large excavators, such as big parrotfish, are considered to be <a href="http://rspb.royalsocietypublishing.org/content/early/2011/11/15/rspb.2011.1906">particularly important</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/146856/original/image-20161121-4515-z66nmw.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/146856/original/image-20161121-4515-z66nmw.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/146856/original/image-20161121-4515-z66nmw.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/146856/original/image-20161121-4515-z66nmw.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/146856/original/image-20161121-4515-z66nmw.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/146856/original/image-20161121-4515-z66nmw.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/146856/original/image-20161121-4515-z66nmw.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"><em>Chlorurus frontalis</em>, a parrotfish that bites into the reef when it feeds, may be particularly important in controlling large algae and opening up new sites for corals to grow.</span>
<span class="attribution"><span class="source">Brian J. Zgliczynski (Scripps Institution of Oceanography)</span></span>
</figcaption>
</figure>
<h2>Which conditions suit which herbivores?</h2>
<p>We used a large-scale ecosystem monitoring data set of underwater visual surveys that were conducted by SCUBA divers for the <a href="https://www.pifsc.noaa.gov/cred/pacific_ramp.php">Pacific Reef Assessment and Monitoring Program</a> at over 3,000 sites at 33 islands and atolls in Hawaii, Central Polynesia and the tropical Northwest Pacific. These sites encompassed a wide range of physical conditions and levels of human population.</p>
<p>By pairing data collected by divers on coral reef fish populations at these sites with satellite-derived data on factors such as sea surface temperature, we were able to separate the relative influence of humans from that of physical and environmental drivers on the biomass of different functional groups of herbivorous fish. Biomass is a measure that includes both the abundance and size of these fish. We modeled biomass because it is sensitive to fishing pressure and conveys information on the state of these functional groups.</p>
<p>Human impacts on herbivores were clearly evident in this study. As human population density increased, the total biomass of all types of herbivorous fish on nearby coral reefs declined rapidly. We also found that this was true for some of our subgroups: Locations with more people had fewer browsers and large excavators. These species tend to grow to large sizes and live relatively longer than other herbivores, so they are both more heavily targeted and more vulnerable to fishing. </p>
<p>However, for several of the other groups we studied, environmental conditions influenced their biomass more strongly than human impacts. In areas with higher sea surface temperatures, browsing fishes were less common and detrivores were more prevalent. Additionally, browsers and large excavators were 24 to 45 percent more abundant on reefs around low-lying islands and atolls than on reefs near high islands. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/146854/original/image-20161121-4552-1lu912d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/146854/original/image-20161121-4552-1lu912d.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=214&fit=crop&dpr=1 600w, https://images.theconversation.com/files/146854/original/image-20161121-4552-1lu912d.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=214&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/146854/original/image-20161121-4552-1lu912d.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=214&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/146854/original/image-20161121-4552-1lu912d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=268&fit=crop&dpr=1 754w, https://images.theconversation.com/files/146854/original/image-20161121-4552-1lu912d.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=268&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/146854/original/image-20161121-4552-1lu912d.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=268&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Summary of the main results from this analysis. E = large excavating parrotfishes, B = browsers, D = detritivores.</span>
</figcaption>
</figure>
<h2>Location, location, location</h2>
<p>Since the groups of herbivores we studied play different functional roles on reefs, healthy reefs are likely to need diverse populations of grazing fishes. Browsers and large parrotfish are most sensitive to human impacts, so our results suggest that we may need new strategies to protect these species.</p>
<p>Our findings also show that a coral reef’s environmental setting strongly influences the number and diversity of herbivorous caretaker species that it can support. For instance, browsers that feed directly on macroalgae are naturally increased in cooler locations, while detritivores that selectively remove detritus from algal turfs (thus keeping the turfs clean) have increased population sizes in warmer areas.</p>
<p>Agencies that manage coral reefs are increasingly turning to local-scale interventions to help make these sensitive ecosystems more sustainable. Some may adopt policies that focus on herbivores, such as the <a href="http://www.kahekilimarinereserve.com/">marine reserve on the Hawaiian island of Maui</a> where herbivores, but not other species, are protected from fishing. Our results show that it is important to treat herbivores as a diverse group with different roles and vulnerabilities, and to think about the environmental context as we design strategies to protect them.</p><img src="https://counter.theconversation.com/content/69195/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adel Heenan receives funding from the NOAA Coral Reef Conservation Program. </span></em></p><p class="fine-print"><em><span>Andrew Hoey receives funding from the Australian Research Council Centre of Excellence for Coral Reef Studies.</span></em></p><p class="fine-print"><em><span>Gareth J Williams received funding from the Gordon and Betty Moore Foundation. </span></em></p><p class="fine-print"><em><span>Ivor D Williams receives funding from NOAA Coral Reef Conservation Program.</span></em></p>Plant-eating fish control the spread of seaweed and algae on coral reefs. New research explaining why populations of these fish vary from site to site could lead to better reef protection strategies.Adel Heenan, Affiliate Researcher in Ecology, National Oceanic and Atmospheric AdministrationAndrew Hoey, Senior Research Fellow, James Cook UniversityGareth J. Williams, Lecturer, Marine Biology, Bangor UniversityIvor D. Williams, Coral Reef Ecologist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/670632016-10-27T00:12:28Z2016-10-27T00:12:28ZWill the Great Barrier Reef recover from its worst-ever bleaching?<figure><img src="https://images.theconversation.com/files/143238/original/image-20161026-11236-1niwebj.JPG?ixlib=rb-1.1.0&rect=229%2C256%2C3418%2C2086&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Bleached corals are still alive, but they are starving, and often die in the following weeks.</span> <span class="attribution"><span class="source">Greg Torda</span>, <span class="license">Author provided</span></span></figcaption></figure><p>A <a href="http://www.gbrmpa.gov.au/media-room/coral-bleaching">fifth of the Great Barrier Reef’s corals are dead</a> after the worst bleaching event on record. Most of these deaths occurred in the northern part of the reef above Lizard Island. </p>
<p>Months after the bleaching event, research teams are now taking stock of the damage. Corals can recover from bleaching. But in a changing world they will have less time to do so before the next event. </p>
<h2>Bleaching 101</h2>
<p>Reef-building corals are animals that live symbiotically with one-celled algae (a species of dinoflagellate known as <a href="https://en.wikipedia.org/wiki/Symbiodinium">Symbiodinium</a>, or colloquially as zooxanthellae). </p>
<p>The coral host provides safe habitat within its cells and supplies nutrients, while the algae in return feeds the coral with products from photosynthesis. This partnership is highly efficient. It allows stony corals that require a lot of energy to produce their skeletons to thrive in nutrient-poor tropical waters. But it is also a fragile balance. </p>
<p>Environmental stress, most commonly caused by increased water temperatures and elevated light conditions, can cause the zooxanthellae to produce <a href="https://en.wikipedia.org/wiki/Reactive_oxygen_species">too much reactive oxygen species</a>, which is toxic to the coral. So the coral expels the algae.</p>
<p>This is what is actually happening when a coral “<a href="http://www.gbrmpa.gov.au/managing-the-reef/threats-to-the-reef/climate-change/what-does-this-mean-for-species/corals/what-is-coral-bleaching">bleaches</a>”. Expelling 90% or more of the algae, the coral’s skeleton becomes visible through its tissues. </p>
<p>A bleached coral can stay alive but is deprived of its primary food source and will begin to starve. Its metabolism suffers, the immune system becomes compromised, it becomes more susceptible to disease, and defence against coral predators, such as snails known as <a href="http://www.reefresilience.org/coral-reefs/stressors/predator-outbreaks/drupella/">Drupella</a>, is weakened. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/143185/original/image-20161025-4714-gdjir2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/143185/original/image-20161025-4714-gdjir2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/143185/original/image-20161025-4714-gdjir2.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/143185/original/image-20161025-4714-gdjir2.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/143185/original/image-20161025-4714-gdjir2.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/143185/original/image-20161025-4714-gdjir2.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/143185/original/image-20161025-4714-gdjir2.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">Survivors of the bleaching are suffering from increased predation pressure. Drupella snails aggregate on the remaining live corals around Lizard Island following the 2016 bleaching event.</span>
<span class="attribution"><span class="source">Greg Torda</span></span>
</figcaption>
</figure>
<p>Depending on the intensity and duration of environmental stress, corals can die from the immediate impacts of a severe heat stress; starvation; disease or being eaten. </p>
<p>If conditions get better, corals can regain their symbiotic algae – and with it their brownish colour - from the surrounding water or from the multiplication of the remnant algae within their cells. In this way individual coral colonies can recover. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/143182/original/image-20161025-4717-12u5twr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/143182/original/image-20161025-4717-12u5twr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/143182/original/image-20161025-4717-12u5twr.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/143182/original/image-20161025-4717-12u5twr.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/143182/original/image-20161025-4717-12u5twr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/143182/original/image-20161025-4717-12u5twr.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/143182/original/image-20161025-4717-12u5twr.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Corals weakened by heat stress are more susceptible to coral diseases. Here, skeletal eroding band disease is slowly killing a Pocillopora colony in the aftermath of the 2016 bleaching event.</span>
<span class="attribution"><span class="source">Greg Torda</span></span>
</figcaption>
</figure>
<p>Different coral species bleach at different stress levels, and some species are more likely to die directly from the conditions that cause bleaching. </p>
<p>For example, the fastest-growing corals are highly effective at capturing light to feed their algal fuel cells. Even under normal conditions they are living close to their maximum tolerance of temperature and light. These corals are far more susceptible to more light and temperature than other, slower growing corals.</p>
<p>Incidentally, these fast-growing corals are also the ones that provide the bulk of the intricate three-dimensional structure to the reef that is critical to most reef critters, including fish. Because of their enhanced metabolism, fast-growing corals also die in greatest numbers during bleaching events, therefore they have been considered the losers of coral bleaching. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/143180/original/image-20161025-4735-1c3t7da.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/143180/original/image-20161025-4735-1c3t7da.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/143180/original/image-20161025-4735-1c3t7da.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/143180/original/image-20161025-4735-1c3t7da.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/143180/original/image-20161025-4735-1c3t7da.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/143180/original/image-20161025-4735-1c3t7da.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/143180/original/image-20161025-4735-1c3t7da.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">Field of recently dead staghorn corals. These corals still provide habitat for some reef critters, but will soon erode to rubble.</span>
<span class="attribution"><span class="source">Greg Torda</span></span>
</figcaption>
</figure>
<h2>Reef recovery</h2>
<p>Due to the variability in bleaching and coral deaths, even moderate bleaching events can decrease the amount of live coral on the reef’s structure and can dramatically alter the species composition. </p>
<p>The recovery of the reef after a disturbance, such as a bleaching event, happens when the amount of live coral covering the reef, the structural complexity, and the composition of the coral community all return to the levels prior to disturbance.</p>
<p>This requires the re-colonisation of the reef by coral propagules (larvae or fragments) that grow into large mature colonies over the course of years and decades. </p>
<p>In severe bleaching events, such as the most recent 2016 mass bleaching event on the Great Barrier Reef and in parts of the remote Pacific Ocean, even the more thermally-tolerant, slow-growing corals severely bleached; several locations suffered large numbers of coral deaths. </p>
<p>The loss of slow growing corals is particularly alarming, because replacing these colonies will require decades, and in some cases centuries, to return the reefs to what they were just a short time ago. </p>
<p>It is unlikely that the reefs affected by the 2016 event in the northern Great Barrier Reef will recover for many decades. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/143179/original/image-20161025-4721-1yopfxj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/143179/original/image-20161025-4721-1yopfxj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/143179/original/image-20161025-4721-1yopfxj.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/143179/original/image-20161025-4721-1yopfxj.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/143179/original/image-20161025-4721-1yopfxj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/143179/original/image-20161025-4721-1yopfxj.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/143179/original/image-20161025-4721-1yopfxj.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">Other symbiotic organisms such as this anemone can also bleach when stressed.</span>
<span class="attribution"><span class="source">Greg Torda</span></span>
</figcaption>
</figure>
<h2>Will there be a next time?</h2>
<p>It is highly unlikely that reefs will get the decades they need to recover – in fact, the frequency of bleaching events is increasing. </p>
<p>Current trends in <a href="https://www.ncdc.noaa.gov/cag/time-series/global/shem/ocean/ytd/12/1880-2014">ocean temperature</a> and future predictions suggest bleaching will occur each year within the coming decades. Some reefs around the world have just experienced consecutive years of bleaching, with barely any opportunity for colonies, let alone reefs, to recover.</p>
<p>Can corals adapt or acclimatise to elevated water temperatures over the course of a few years? Corals inhabiting unusually warm waters, such as the <a href="https://en.wikipedia.org/wiki/Persian_Gulf">Persian Gulf</a> and some areas of the <a href="http://www.worldwildlife.org/places/coral-triangle">Coral Triangle</a>, demonstrate that long-term adaptation to a high temperature regime has been possible. </p>
<p>However, evidence to date suggests that these adaptive processes are unlikely to be able to keep up with climate change.</p>
<p>Action to reduce atmospheric CO<sub>2</sub> levels, and halt the associated warming, must be quickly and vigorously pursued to avert the predicted degradation of coral reefs. If this is not undertaken, the consequences for reefs will only be amplified from what we have seen this year.</p><img src="https://counter.theconversation.com/content/67063/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tracy Ainsworth receives funding from The Australian Research Council Discovery Program and the ARC Center of Excellence for Coral Reef Studies. </span></em></p><p class="fine-print"><em><span>Greg Torda receives funding from the Australian Research Council. He is also affiliated with the Australian Institute of Marine Science. </span></em></p><p class="fine-print"><em><span>Scott Heron receives funding and support from the U.S. National Oceanic and Atmospheric Administration's Satellites division (NESDIS) and Coral Reef Conservation Program, and is affiliated with James Cook University. The contents in this piece are solely the opinions of the authors and do not constitute a statement of policy, decision or position on behalf of NOAA or the U.S. Government.</span></em></p>Months after record breaking coral bleaching, research teams are taking stock of the damage on the Great Barrier Reef.Tracy Ainsworth, Research Fellow, ARC Centre of Excellence for Coral Reef Studies, James Cook UniversityGreg Torda, Postdoctoral research fellow, James Cook UniversityScott F. Heron, Physical Scientist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/615012016-09-16T01:05:47Z2016-09-16T01:05:47ZAs climate change alters the oceans, what will happen to Dungeness crabs?<figure><img src="https://images.theconversation.com/files/135675/original/image-20160827-17859-6svpgw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Live crab at a Seattle market</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-271735067/stock-photo-seafood-market-live-dungeness-crabs-live-dungeness-crabs-for-sale-at-a-seattle-market.html">Shutterstock.com</a></span></figcaption></figure><p>Many travelers visit the Pacific Northwest to eat the region’s famous seafood – particularly Dungeness crabs, which are popular in crab cakes or wrestled straight out of the shell. Locals also love catching and eating the feisty creatures. One of my favorite ways to spend an afternoon is fishing for Dungeness crabs from a pier in Puget Sound with my daughter. We both enjoy the anticipation of not knowing what we will discover when we pull up the trap. For us, the mystery is part of the fun. </p>
<p>But for commercial crabbers who bring in one of the most valuable marine harvests on the U.S. West Coast, that uncertainty affects their economic future. </p>
<p>In my day job as a research ecologist with the National Oceanic and Atmospheric Administration’s <a href="https://www.nwfsc.noaa.gov/">Northwest Fisheries Science Center</a>, I study how changes in seawater’s acidity from absorbing carbon dioxide in the air, referred to as <a href="https://theconversation.com/global-warmings-evil-twin-ocean-acidification-19017">ocean acidification</a>, may affect the success of recreational crabbers like me and the fortunes of the crabbing industry. </p>
<p>Contrary to early assumptions that acidification was unlikely to have significant effects on Dungeness crabs, we found <a href="http://dx.doi.org/10.1007/s00227-016-2883-1">in a recent study</a> that the larvae of this species have lower survival when they are reared in the acidified ocean conditions that we expect to see in the near future. Our findings have sobering implications for the long-term future of this <a href="http://www.psmfc.org/crab/2014-2015%20files/DUNGENESS%20CRAB%20REPORT2014.pdf">US$170 million fishery</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/137969/original/image-20160915-30605-1o3jpye.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/137969/original/image-20160915-30605-1o3jpye.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/137969/original/image-20160915-30605-1o3jpye.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/137969/original/image-20160915-30605-1o3jpye.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/137969/original/image-20160915-30605-1o3jpye.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/137969/original/image-20160915-30605-1o3jpye.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/137969/original/image-20160915-30605-1o3jpye.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Pike Place Market, Seattle.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/jpellgen/6359094679/in/photolist-aFW2ir-p1YBm-9nAAz8-9p7zAu-b9Zy4x-cqQfpJ-6FsLvU-ygqkb-AgvNo-b9ZxUM-cuE1um-fwf7Fm-4Kbhas-oLJWTr-5cEJmt-a5uTdy-4KbgS5-4KbgrW-4KbjZ7-5ph23B-4K73wp-4Kbgkb-9Dq6Y2-9p7zAy-bPYjvz-8Lq3s1-4WzvEc-eeime-54xaEx-4y9US-2XVQzH-56B8WF-6FoGiz-i6Hpy-8LmZxT-eSy8h9-duvq7o-5n4no2-7XikAq-7v9DrE-4K76G2-4K74mM-4KbgLA-4K75iT-4K74GX-4K7512-4K75Ka-4K762B-4K76jr-4K76VX">jpellgen/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Dissolving shells</h2>
<p>Ocean acidification is a global phenomenon that occurs when we burn fossil fuels, pumping carbon dioxide (CO2) into the atmosphere. Some of that CO2 is absorbed by the ocean, causing chemical changes that make ocean water more acidic, which can affect many types of marine life. The acidification taking place now is the most rapid change in ocean chemistry in at least 50 million years.</p>
<p>Many organisms, including numerous species of fish, phytoplankton and jellyfish, do not seem to be greatly affected by these changes. But some species – particularly oysters, corals and other organisms that make hard shells from calcium carbonate in seawater – die at a higher rate as the water in which they are reared becomes more acidic. Acidification reduces the amount of carbonate in the seawater, so these species have to use more energy to produce shells. </p>
<p>If water becomes extremely acidic, their shells can literally dissolve. We have seen this happen in <a href="http://dx.doi.org/10.1371/journal.pone.0105884">experiments</a> using small free-swimming marine snails called pteropods. </p>
<p>Dungeness crabs make their exoskeleton primarily from chitin, a modified polysaccharide similar to cellulose, that contains only small amounts of calcium carbonate. Initially, scientists predicted that the species would experience relatively limited harm from acidification. However, recent experiments in our lab led by graduate student Jason Miller suggest that Dungeness crabs are also vulnerable. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/137971/original/image-20160915-30605-12e4c3r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/137971/original/image-20160915-30605-12e4c3r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/137971/original/image-20160915-30605-12e4c3r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/137971/original/image-20160915-30605-12e4c3r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/137971/original/image-20160915-30605-12e4c3r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/137971/original/image-20160915-30605-12e4c3r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/137971/original/image-20160915-30605-12e4c3r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Crab fishing boats, Half Moon Bay, California.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/presta/5324492504/in/photolist-97vq7U-fz72qz-8TbVXQ-9CqCNb-6n6AGK-7b8QFx-485sJL-9CnGGH-7Vzapj-7Vzaiq-7Vzajb-7b8Rca-6uJuA4-9CqCzo-9QgjQE-9QfQjU-F3jWAB-FxtkMy-FXAaQ6-FPpfRA-F3m6wa-FRHKeP-7PNbE9-9Cr9em-aP43kT-cN2UvQ-9CoeR2-oLt3cY-9Cr9bf-966ceW-9CnHTz-aeUHRy-7VvVSX-99UvXJ-9CoeMt-9Cr9tW-eN8th8-9CnGkp-bpzuDz-9CnGpi-9CqBxj-9CqChy-9CnHM4-9Cof2n-5pK7iR-7VvVRV-9CqCef-9Cr9EA-9CnGyc-9CqBn1">Steve McFarland/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>Fewer crabs, growing more slowly</h2>
<p>In these experiments we simulated CO2 conditions that have been observed in today’s ocean and conditions we expect to see in the future as result of continued CO2 emissions. By raising Dungeness crab larvae in this “ocean time machine,” we were able to observe how rising acidification affected their development.</p>
<p>Dungeness crabs’ life cycle starts in autumn, when female crabs each produce up to two million orange eggs, which they attach to their abdomens. The brooding females spend the winter buried up to their eye stalks in sediment on the sea floor with their egg masses tucked safely under a flap of exoskeleton. </p>
<p>In spring the eggs hatch, producing larvae in what is called the zoea stage – about the size of a period in 12-point type. Zoea-stage crab larvae look nothing like adult crabs, and have a completely different lifestyle. Instead of lurking on the bottom and scavenging on shrimp, mussels, small crabs, clams and worms, they drift and swim in the water column eating smaller free-swimming zooplankton. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/137973/original/image-20160915-30580-b1mscg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/137973/original/image-20160915-30580-b1mscg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=469&fit=crop&dpr=1 600w, https://images.theconversation.com/files/137973/original/image-20160915-30580-b1mscg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=469&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/137973/original/image-20160915-30580-b1mscg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=469&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/137973/original/image-20160915-30580-b1mscg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=590&fit=crop&dpr=1 754w, https://images.theconversation.com/files/137973/original/image-20160915-30580-b1mscg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=590&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/137973/original/image-20160915-30580-b1mscg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=590&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Dungeness crab larva, zoea stage.</span>
<span class="attribution"><a class="source" href="http://www.dfw.state.or.us/mrp/shellfish/crab/lifehistory.asp">Oregon Department of Fish and Wildlife</a></span>
</figcaption>
</figure>
<p>After molting through five different zoea stages, which all look pretty similar, the larvae reach the megalopae stage when they are about two months old. Next they molt into the benthic juvenile stage, which looks a lot like an adult crab, and settle to the sea floor. The crabs finally reach adulthood about two years after hatching.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/135360/original/image-20160824-30228-adsn4k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/135360/original/image-20160824-30228-adsn4k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1217&fit=crop&dpr=1 600w, https://images.theconversation.com/files/135360/original/image-20160824-30228-adsn4k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1217&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/135360/original/image-20160824-30228-adsn4k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1217&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/135360/original/image-20160824-30228-adsn4k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1530&fit=crop&dpr=1 754w, https://images.theconversation.com/files/135360/original/image-20160824-30228-adsn4k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1530&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/135360/original/image-20160824-30228-adsn4k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1530&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Some common pH values.</span>
<span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/thumb/2/23/216_pH_Scale-01.jpg/378px-216_pH_Scale-01.jpg">Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>In our experiment, divers collected brooding female Dungeness crabs from the bottom of Puget Sound in Washington state. We reared larvae produced from these females in three different CO2 levels that roughly corresponded to acidification levels now (pH 8.0), levels projected to be relatively common at midcentury (pH 7.5) and levels expected in some locations by the end of the century (pH 7.1). The pH scale measures how acidic or basic (alkaline) a substance is, with lower pH indicating a more acidic condition and a decrease of one unit (i.e., from 8 to 7) representing a tenfold increase in acidity. This means that the ocean today (average pH 8.1) is about 25 percent more acidic than the ocean in pre-industrial times (pH 8.2) and the ocean of the future is expected to be about 100 percent more acidic than today. </p>
<p>Describing exactly how acidic Puget Sound is now or could be in the future is complicated, because CO2 levels in different parts of the Sound vary widely and there are seasonal shifts. Generally, however, Puget Sound is <a href="http://www.pmel.noaa.gov/co2/story/Acidifying+Water+Takes+Toll+On+Northwest+Shellfish">naturally more acidic than other parts of the ocean</a> because currents bring acidic waters from the deep ocean to the surface there. But shellfishermen are concerned because human-produced CO2 is causing large changes on top of these background levels of variation.</p>
<p>We found that although eggs reared in high-CO2 water hatched at the same rate as those in lower-CO2 water, fewer than half as many of the larvae reared in highly acidic conditions survived for more than 45 days compared to those raised under current conditions (Figure 2). Put another way, the mortality rate in acidified conditions was more than twice as high as in more contemporary CO2 conditions. Crabs raised in more acidic water also developed more slowly, and fewer of them reached the 4th zoeal stage compared to larvae raised in less-acidic water. This slower development rate probably reflected the extra energy that larvae had to expend to grow in a more acidic environment.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/132888/original/image-20160803-17173-is5dll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/132888/original/image-20160803-17173-is5dll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=892&fit=crop&dpr=1 600w, https://images.theconversation.com/files/132888/original/image-20160803-17173-is5dll.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=892&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/132888/original/image-20160803-17173-is5dll.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=892&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/132888/original/image-20160803-17173-is5dll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1121&fit=crop&dpr=1 754w, https://images.theconversation.com/files/132888/original/image-20160803-17173-is5dll.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1121&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/132888/original/image-20160803-17173-is5dll.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1121&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="https://www.nwfsc.noaa.gov/news/features/ocean_acidification_dungeness_crab/index.cfm">Su Kim/NOAA Fisheries</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We are not entirely sure what these results mean for future populations of Dungeness crabs, but there is reason for concern. Significantly lower larval survival may translate into fewer adult crabs, which will have ripple effects on the fishery and Pacific coastal food webs. </p>
<p>Slower larval growth could lead to a mismatch in the timing of predators and prey. Crab larvae depend on finding abundant prey during certain times of the year, and organisms such as Chinook salmon and herring that prey on crab larvae depend on an abundance of crabs at particular times of the year. Any factor that disrupts the timing of development can have important ecological consequences. </p>
<p>Dungeness crab are found along the Pacific coast from California to Alaska, and over that range they experience wide variations in water temperature, ecological communities and pH. It is possible that individual crabs may be able to tolerate new CO2 conditions during their lives – in other words, to acclimate to the changes. Or if some crabs are just better able to tolerate high-CO2 conditions more easily than others, they may pass on that ability to their offspring, allowing the species to adapt to rising acidification through evolution. Our next studies will examine how Dungeness crabs may acclimate or adapt to increasing acidification. </p>
<p>Today Dungeness crab populations are generally in good condition, and my daughter and I usually come home from our crabbing adventures victorious. It is hard to imagine that this abundant species is at risk in the coming decades, but we need to anticipate how it could be affected by acidification. For Dungeness crabs and many other species, it is essential to understand how human actions today could alter sea life in tomorrow’s oceans.</p>
<p><em>Jason Miller, a former biologist at NOAA’s Northwest Fisheries Science Center and graduate student at the University of Washington, was lead author of the Dungeness crab larval exposure study on which much of this article is based.</em></p><img src="https://counter.theconversation.com/content/61501/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul McElhany receives funding from the NOAA Ocean Acidification Program and the Washington Ocean Acidification Center. </span></em></p>Global climate change is altering the chemistry of the oceans. A recent study suggests that the Pacific coast’s lucrative Dungeness crab fishery could suffer as ocean water becomes more acidic.Paul McElhany, Research Ecologist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/535972016-01-27T10:45:55Z2016-01-27T10:45:55ZThe cheapest way to scale up wind and solar energy? High-tech power lines<figure><img src="https://images.theconversation.com/files/109263/original/image-20160126-28853-17j9kw2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/reupa/18867280344/in/photolist-uKeK7Y-9wh4as-p4m94T-6stiUa-7xLkkZ-nwwdT4-efLk43-9iRdBv-9jc4u1-dzZV2j-dj7KAE-dzUrAg-pskKMf-bUiU4r-bdnAU4-dHMVuu-93q5r-pWuifg-j7Grdk-ab9Puq-bnvLP3-6wEga9-kUhbi3-cbF7MJ-e3oTe7-bUk3dE-jWDuMF-c9BtzG-txocRk-dgvmRY-7cY1PG-bUiUkB-BDRJJE-mK5zQU-a335b5-oxzJxn-dLHw5m-gvaEaS-9AWQvk-5G5h4A-qHiKNa-agXw2S-bideM6-jJuG2N-myzDto-cQEn4U-7rwYup-og6fvf-ajYATR-ovxV9u">reupa/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Wind power and solar power are ways to reduce carbon emissions, but these generation sources are dependent on the vagaries of the weather, which means neither wind nor solar can produce electricity on-demand at all hours of the day. This variability has led many to assume that greatly expanding wind and solar to reduce carbon emissions will cause electricity costs to skyrocket and require expensive energy storage.</p>
<p>My colleagues and I have just published a <a href="http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2921.html">new study</a> to show that this assumption is not correct. In fact, if the U.S. were to move to a national 48-state electric system, rather than the regional one in place now, the country would be able to transport more renewable energy around the country. That change could reduce CO2 by 78 percent at lower costs than today without using any storage technologies. </p>
<p>Using a computer model, we found that this larger electric system would utilize power more efficiently regardless of the generators within it. The cost reduction between the national style system we modeled and the current one, which is divided into about 130 regions, is US$47 billion per year. That translates into an electricity cost of between 8.5 and 10.2¢ per kilowatt-hour (kWh), compared to the current national average of <a href="https://www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_5_6_a">12.7 cents per kWh</a>.</p>
<h2>Electron superhighway</h2>
<p>Our study was based upon a model called the National Energy with Weather System (NEWS) simulator. The <a href="http://www.esrl.noaa.gov/gsd/renewable/news-simulator.html">NEWS simulator</a> is a <a href="http://www.esrl.noaa.gov/gsd/renewable/news-results.html">cost optimization model</a> that relentlessly seeks the lowest-cost solution. </p>
<p>It includes features of the electric grid, such as transmission, generators, electric demand, land use constraints, generator behavior, weather data and cost data for generators. To figure out how to minimize costs, the NEWS model will calculate how to supply power every single hour for an entire year based on the available generators and transmission lines that transport power long distances.</p>
<p>Our model had something unique, though: a high-voltage direct current (HVDC) transmission overlay. </p>
<p>In concept, this is very similar to the interstate highway system overlaid upon the road network. HVDC technology has one big advantage over traditional power lines: there is less energy lost in transporting power from one point to another. It does this by using direct current, rather than alternating current, and operating at higher voltages. </p>
<p>HVDC is being used in the U.S. today. However, it is being deployed as a point-to-point system for single (or a few) generators to distant markets. One of the most prominent is called the Pacific DC intertie, which ships power from the Pacific Northwest, with its abundant hydropower, down to Los Angeles, supplying <a href="http://new.abb.com/systems/hvdc/references/pacific-intertie">48 percent of power during hours of peak demand</a>. The difference in the NEWS model is that HVDC is deployed in a network, instead of a simple point-to-point configuration, which allows much greater utilization of the lines for power to flow between regions in multiple directions.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/109186/original/image-20160126-19667-1tixd5d.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/109186/original/image-20160126-19667-1tixd5d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/109186/original/image-20160126-19667-1tixd5d.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=353&fit=crop&dpr=1 600w, https://images.theconversation.com/files/109186/original/image-20160126-19667-1tixd5d.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=353&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/109186/original/image-20160126-19667-1tixd5d.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=353&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/109186/original/image-20160126-19667-1tixd5d.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=444&fit=crop&dpr=1 754w, https://images.theconversation.com/files/109186/original/image-20160126-19667-1tixd5d.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=444&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/109186/original/image-20160126-19667-1tixd5d.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=444&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Wind power potential estimates for the U.S. Red indicates high potential, blue is low.</span>
<span class="attribution"><span class="source">Chris Clack / CIRES</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Critically, the NEWS model doesn’t assume that more transmission lines should be added to the current grid. But it does introduce new transmission capacity if the model deems it economical. Interestingly, the NEWS model always selects HVDC transmission when it can. Why? The availability of HVDC lines allows bigger markets to form, which then benefit from economies of scale. </p>
<p>In practice, this would mean that wind generators in the Plains states, for instance, could export more power to places in the country where there is strong demand, such as big cities. As it is now, wind generators only support power regionally and sometimes supply more power than is needed at some hours of the day. </p>
<p>In a regional system, one that is the size of, say, Kansas, wind and solar tends to be periods of over production periods and under production. This results in increased costs because wind and solar generators need to curtailed, or turned off, during over production. To meet lapses in production, grid operators need to rely on back up generation from fossil fuel plants. </p>
<p>With a national system, the generators can be strategically placed over the contiguous U.S. to reduce this effect and lower the overall costs. The HVDC facilitates the movement of this electricity from distant reaches to cities with lower losses than traditional AC. </p>
<h2>Renewables scenario</h2>
<p>To perform the study, high-resolution weather data were compiled for each hour of the three years from 2006 through 2008. The weather data were then used as inputs into sophisticated power algorithms to estimate the power that could be generated by wind turbines and solar PV panels across the U.S.</p>
<p>Additionally, we compiled data on electricity demand during those times across the U.S. The data were needed because weather is a fundamental driver of the electric demand. Then we projected demand data to 2030. </p>
<p>Because the deployment of wind and solar is subject to many constraints, we built land use considerations into the model. A land use data set was compiled to identify locations where the wind and solar can be deployed without interfering with protected lands.</p>
<p>Using these different sets of data along with the projected cost for power generation in 2030, we ran different simulations to investigate how these factors would affect the mix of power generators regionally while minimizing total cost. </p>
<p>The scenario that cuts emissions most has significant wind and solar PV deployed; 523 gigawatts (GW) of wind and 371 gigawatts of solar PV compared with 60 GW and 2.5 GW, respectively, in 2012. In this scenario, there was only 461 GW of natural gas (less than today). </p>
<p>This translates to 38 percent of electricity coming from wind, 17 percent from solar, 21 percent from natural gas and the remainder from nuclear and hydroelectric. In 2012, wind accounted for 3.5 percent, solar for less than 1 percent and natural gas for 30 percent.</p>
<p>Again, this solution is the cheapest possible solution. </p>
<p>To get to this level of solar and wind – a significant jump from today’s levels – does require new transmission lines in the model. </p>
<p>The amount of new HVDC transmission that is built by the model is 139 million MW-miles, which is a big infrastructure undertaking. This sounds like a huge amount, but it would represent only 4 percent of the total cost of the system annually.</p>
<h2>What about energy storage?</h2>
<p>The NEWS model is unique in the study of integrating higher levels of wind and solar because it handles huge volumes of weather data, while computing the important aspects of the electric grid such as ramping constraints on generators, down times for generators, power flow in the transmission lines, electric losses shuffling power around the system, meeting demand at each hour in every market and other operating constraints. Further, the model doesn’t exclude any technologies; it seeks only the lowest-cost options. </p>
<p>Electricity can be stored in a number of ways, such as pumping and releasing water from reservoirs or installing large battery banks. In initial model runs, electric storage was not competitive using cost estimates for 2030 compared to adding transmission or natural gas generators (purely based upon cost). </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/109266/original/image-20160126-19641-16u7f6d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/109266/original/image-20160126-19641-16u7f6d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/109266/original/image-20160126-19641-16u7f6d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/109266/original/image-20160126-19641-16u7f6d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/109266/original/image-20160126-19641-16u7f6d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/109266/original/image-20160126-19641-16u7f6d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/109266/original/image-20160126-19641-16u7f6d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/109266/original/image-20160126-19641-16u7f6d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&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 battery bank used to store electricity from the grid.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/departmentofenergy/14669268664/in/photolist-kwut5s-kwut5N-kwus2W-kwusJN-kwuswy-gy1ikJ-omgQiw-o4YgUZ-o4XbHD-omgQvf-fj6t7K-omgQpy-omgQjo-ooeNK2-o4YBMz-o4YBXK-omgQzy-o4YC4r-bzDXmM-fzkWkC-fzkWmd-fgxvCX-fF83J7">U.S. Department of Energy</a></span>
</figcaption>
</figure>
<p>The NEWS model is a tool to help understand how an electric grid could be transformed while keeping costs low. Low cost is absolutely essential because increasing energy costs to reduce carbon reductions can cause economic hardships. </p>
<p>There are numerous headwinds to the development of a decarbonized economy and society. But, the NEWS model has shown that wind and solar PV, combined with high-voltage direct current transmission, can actually go a long way in reducing emissions in the electric sector. </p>
<p>This is true even without a new miracle battery or innovation within the electric storage industry, although cheap, effective electric storage would be helpful in integrating renewables. </p>
<p>To remove carbon from the entire economy, electricity must be decarbonized first. If it can be done at low cost, then other sectors will be able to follow suit. Combining wind, solar, natural gas and transmission is a possible bridge to a zero emissions future.</p><img src="https://counter.theconversation.com/content/53597/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher Clack does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The U.S. could dramatically increase solar and wind power without expensive energy storage. The key is to overlay high-voltage direct current power lines on our system of regional grids.Christopher Clack, Research Scientist, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/428072015-06-04T18:33:39Z2015-06-04T18:33:39ZImproved data set shows no global warming ‘hiatus’<figure><img src="https://images.theconversation.com/files/83994/original/image-20150604-3397-noi9ha.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">New data set includes more accurate data from the Arctic, where more warming has occurred.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/gsfc/5937599688/">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>National and international studies have shown that the Earth is warming, and with this warming, other changes are occurring, such as an increasing incidence of heat waves, heavy downpours and rising sea levels. </p>
<p>In its <a href="https://www.ipcc.ch/report/ar5/wg1/">Fifth Assessment Report</a> in 2013, the Intergovernmental Panel on Climate Change <a href="https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter02_FINAL.pdf">found</a> that the temperature of the Earth increased at a rate of 0.22 Fahrenheit (0.12 Celsius) per decade from 1951-2012. It also found that the rate of warming from 1998-2012 had slowed to 0.09F (0.05C) per decade.</p>
<p>This slowdown in the rate of warming, called a “hiatus,” was initially perplexing to climate scientists. It was inconsistent with expectations that global temperatures would rise at similar or even greater rates than they had in the latter half of the 20th century as the concentration of greenhouse gases in the atmosphere continued to rise.</p>
<p>In an article <a href="http://www.sciencemag.org/content/early/2015/06/03/science.aaa5632.full">published in Science Express</a> on June 4, my colleagues and I at NOAA’s National Centers for Environmental Information (NCEI) presented updated findings that show no hiatus in the rate of warming. Using newly developed data sets of land and ocean temperatures and two additional years of data, we conclude that the global surface temperature increased at a rate of 0.19F (0.106C) per decade from 1998-2014, similar to the rate of 0.20F (0.113C) per decade from 1950-1999.</p>
<p>There were a number of <a href="https://theconversation.com/is-global-warming-in-a-hiatus-18367">proposed explanations</a> for the hiatus, including natural variability and <a href="https://theconversation.com/heat-accumulating-deep-in-the-atlantic-has-put-global-warming-on-hiatus-30805">heat accumulating in the oceans</a>. Although these studies are still equally valid, we expect our finding to provide additional clarity and answers to this question.</p>
<h2>From buckets to buoys</h2>
<p>This conclusion was a result of NCEI’s ongoing efforts to improve the observational climate record through periodic updates to its climate data sets. We recently completed development of version 4 of the Extended Reconstructed Sea Surface Temperature data set (it will be released operationally and available on June 18) and also improved the global record of land surface air temperature data through development efforts that were part of the <a href="http://www.surfacetemperatures.org/">International Surface Temperature Initiative</a>. </p>
<p>The ERSST data set provides global observations of sea surface temperature from the 1800s to present. Much of the data comes from measurements taken by ships at sea. From the earliest records of sea surface temperature, measurements were made by dropping a bucket over the side of the ship, bringing up some water and measuring the temperature of that water. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/83993/original/image-20150604-3400-cmxdt1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/83993/original/image-20150604-3400-cmxdt1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/83993/original/image-20150604-3400-cmxdt1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=455&fit=crop&dpr=1 600w, https://images.theconversation.com/files/83993/original/image-20150604-3400-cmxdt1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=455&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/83993/original/image-20150604-3400-cmxdt1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=455&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/83993/original/image-20150604-3400-cmxdt1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=572&fit=crop&dpr=1 754w, https://images.theconversation.com/files/83993/original/image-20150604-3400-cmxdt1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=572&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/83993/original/image-20150604-3400-cmxdt1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=572&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">NOAA</span></span>
</figcaption>
</figure>
<p>Just prior to World War II, many ships began switching the method they used to measure temperatures. Rather than using a bucket, they began measuring water temperature at the ship’s engine intakes. The water temperature measured in this way is known to be warmer than if measured using buckets. Because these two methods yield differing temperature measurements, the switch in methodology created an artificial shift, or bias, unrelated to climate in temperature records.</p>
<p>In recent decades, there has been another switch to a greater use of buoys rather than ships for ocean observations. Buoys tend to report a slightly cooler temperature than ships, resulting in another bias between the two sources of data. </p>
<p>To measure the true variation and change in the Earth’s temperature – not changes associated with differing instrumentation and observing techniques – it is necessary to make corrections to the historical temperature record to remove the nonclimatic shifts in temperature. The new version of the ERSST data set more completely accounts for the changes in observing methods and technologies than previous versions, making the data more consistent across time. This makes it possible to compare temperature data collected from locations around the world and over many decades, improving the accuracy of temperature trend estimates.</p>
<h2>No hiatus found</h2>
<p>In addition to the update to its sea surface temperature data, NCEI also has made improvements to its land surface air temperature record. Data from NCEI’s Global Historical Climatology Network Daily and Monthly data sets were combined with other data exchanged as part of the International Surface Temperature Initiative. This enabled NCEI to expand the coverage of temperature observations to areas of the world not previously included in global studies, most notably in the Arctic, where temperatures have been rising most rapidly in recent decades.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/83995/original/image-20150604-3407-1qtg9nm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/83995/original/image-20150604-3407-1qtg9nm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/83995/original/image-20150604-3407-1qtg9nm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/83995/original/image-20150604-3407-1qtg9nm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/83995/original/image-20150604-3407-1qtg9nm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/83995/original/image-20150604-3407-1qtg9nm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/83995/original/image-20150604-3407-1qtg9nm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/83995/original/image-20150604-3407-1qtg9nm.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 rate of warming in the Arctic has been faster than in other parts of the world.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/gsfc/7873358708/">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>With the improvements to the land and ocean data sets and the addition of two more years of data, NCEI scientists found that there has been no hiatus in the global rate of warming. This finding is consistent with the expected effect of increasing greenhouse gas concentrations and with other observed evidence of a changing climate such as reductions in Arctic sea ice extent, melting permafrost, rising sea levels, and increases in heavy downpours and heat waves. </p>
<h2>Underestimating the rate of warming</h2>
<p>This work highlights the importance of data stewardship and continuously striving to improve the accuracy and consistency of temperature data sets.</p>
<p>While these improvements in the land and ocean temperature record reveal a rate of warming greater than previously documented, we also found that our computed trends likely continue to underestimate the true rate of warming. This is due at least in part to a lack of surface temperature observations in large parts of the Arctic where warming is occurring most rapidly.</p>
<p>Preliminary calculations of global temperature trends using estimates of temperatures in the Arctic indicate greater rates of warming than the 1998-2014 trend of 0.19F per decade reported in this study. Future data set development efforts will include a focus on further improvements to the temperature record in this area of the world.</p><img src="https://counter.theconversation.com/content/42807/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jay Lawrimore does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>NOAA review reveals that difficult-to-explain slowdown in higher temperatures from global warming was based on faulty data.Jay Lawrimore, Chief, Data Set Branch, Center for Weather and Climate, NOAA's National Centers for Environmental Information, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/407942015-06-01T06:00:31Z2015-06-01T06:00:31ZHurricane forecast accuracy is improving, but don’t overly focus on the skinny black line<figure><img src="https://images.theconversation.com/files/81279/original/image-20150511-19528-1twovqi.GIF?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Hurricane path forecasts are good, but even the ‘cone of uncertainty’ doesn’t fully describe where the hazards could be.</span> <span class="attribution"><span class="source">National Hurricane Center</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><em>This article is part of The Conversation’s series this month on hurricanes. You can read the rest of the series <a href="https://theconversation.com/us/topics/hurricanes-2015">here</a>.</em></p>
<p>“Don’t focus on the skinny black line” was the trademark admonition of former National Hurricane Center (<a href="http://www.nhc.noaa.gov/">NHC</a>) director Max Mayfield dating back to the 1990s. It’s advice that media and residents of southwest Florida would have done well to heed when Hurricane Charley crossed Cuba in August 2004. Too much attention was paid to a track forecast depicting landfall near Tampa, and too few appreciated that Port Charlotte, only 70 miles to the south, was also under a hurricane warning. Although tropical cyclone forecasts had improved dramatically over the years, they were still far from perfect, as residents of Port Charlotte would soon find out.</p>
<h2>Is the storm headed for me?</h2>
<p>Highly visible successes, such as the dead-on track forecasts for 2003’s Hurricane Isabel, might have contributed to complacency ahead of Charley’s landfall the following year. And as it happens, tropical cyclone motion is a well-understood and relatively simple physical process: Storms are steered by the large-scale atmospheric currents that surround them.</p>
<p>For the past quarter-century, computer models have, for the most part, been able to effectively forecast a hurricane’s track. Using global measurements from a wide array of sensors, they take an estimate of the current state of the atmosphere and use certain physical laws to calculate forward in time to obtain the future position of the hurricane. Track forecasts have steadily improved as ever-increasing quantity and accuracy of atmospheric observations enable us to input more accurate initial conditions, and faster computers allow our numerical models to replicate the increasingly fine detail those observations provide.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/82984/original/image-20150526-24769-uldufc.GIF?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/82984/original/image-20150526-24769-uldufc.GIF?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/82984/original/image-20150526-24769-uldufc.GIF?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/82984/original/image-20150526-24769-uldufc.GIF?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/82984/original/image-20150526-24769-uldufc.GIF?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/82984/original/image-20150526-24769-uldufc.GIF?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/82984/original/image-20150526-24769-uldufc.GIF?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/82984/original/image-20150526-24769-uldufc.GIF?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">National Hurricane Center</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>This progress can be readily seen in the evolution of NHC’s “cone of uncertainty,” which is formed from circles that are expected to enclose the actual position of the storm two-thirds of the time. By this measure, the uncertainty in a hurricane’s track has decreased by nearly 40% over the decade since deadly Hurricane Katrina. The cone has gotten smaller as our forecast accuracy has improved. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/82985/original/image-20150526-24754-zynyqs.GIF?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/82985/original/image-20150526-24754-zynyqs.GIF?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/82985/original/image-20150526-24754-zynyqs.GIF?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/82985/original/image-20150526-24754-zynyqs.GIF?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/82985/original/image-20150526-24754-zynyqs.GIF?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/82985/original/image-20150526-24754-zynyqs.GIF?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/82985/original/image-20150526-24754-zynyqs.GIF?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/82985/original/image-20150526-24754-zynyqs.GIF?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ten years later, we would have had more confidence in the Katrina’s expected path, as evidenced by the smaller ‘cone of uncertainty.’</span>
<span class="attribution"><span class="source">National Hurricane Center</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>While we at the NHC are pleased to see this improvement, of course, we continue to worry that highly successful track forecasts with recent storms such as Irene, Sandy and even 2015’s Ana may lead users to have developed unrealistic expectations. </p>
<h2>But how bad will it be?</h2>
<p>Forecasting hurricane intensity (the highest one-minute average wind associated with the storm), on the other hand, has proven to be more difficult. Readers likely have seen and remember numerous examples of forecast failures. The physics are far more complicated, involving features and processes on the smaller scale of miles or tens of miles, rather than the hundred- or thousand-mile-wide features that govern track.</p>
<p>In the early 1990s, numerical models that successfully forecast track were still hopelessly too coarse for intensity prediction. And there were nowhere near enough observations in and around the hurricane eyewall to get these models off to a good start, even if they <em>had</em> had sufficient resolution. With little objective guidance, forecasters got by on a combination of instinct and experience, until statistical models were developed that looked at how past storms in similar circumstances behaved. But even the statistical models were not as good as an experienced forecaster. It’s not surprising, then, that NHC’s official intensity errors were basically unchanged – locked in around 15 knots above or below the actual wind speeds for the average two-day error – through the decades of the ‘90s and the '00s.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/82988/original/image-20150526-24757-1m0dwc7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/82988/original/image-20150526-24757-1m0dwc7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/82988/original/image-20150526-24757-1m0dwc7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/82988/original/image-20150526-24757-1m0dwc7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/82988/original/image-20150526-24757-1m0dwc7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/82988/original/image-20150526-24757-1m0dwc7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/82988/original/image-20150526-24757-1m0dwc7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/82988/original/image-20150526-24757-1m0dwc7.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 intensity forecast trend is going in the right direction… but can still use some improvement.</span>
<span class="attribution"><a class="source" href="http://www.nhc.noaa.gov/verification/figs/ALinerrtrd.jpg">National Hurricane Center</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>The past few seasons, however, have seen a dramatic lowering of intensity forecast errors, particularly at two days out and longer. To some extent this has simply been good luck – strong wind shear and dry, sinking air have dominated the Atlantic basin in recent seasons and limited the numbers of strong and rapidly strengthening storms – and when storms stay weak, forecast errors tend to be low.</p>
<p>But NOAA’s Hurricane Forecast Improvement Project (<a href="http://www.hfip.org">HFIP</a>), a 10-year program now halfway completed, also deserves a share of the credit. HFIP has supported substantial investments in research, modeling and the development of tools for forecasters, all tightly focused on improving the objective guidance available to the National Hurricane Center.</p>
<p>The National Weather Service’s regional hurricane model, known as <a href="http://www.emc.ncep.noaa.gov/gc_wmb/vxt/">HWRF</a>, has been a particular target for HFIP-supported improvements. With increased resolution (the ability to “see” smaller and smaller atmospheric features), more accurate algorithms for estimating energy exchanges with the ocean and the handling of clouds, and more sophisticated ways of ingesting data from a hurricane’s inner core, the HWRF model has become skilled enough even to beat the NHC human forecasters in some retrospective tests. While it will likely require an active Atlantic hurricane season to truly assess how much progress we’ve made, we’re starting to see real advances. Unfortunately, HFIP <a href="http://www.corporateservices.noaa.gov/%7Enbo/fy15_bluebook/FY2015BudgetSummary-small.pdf#page=29">funding was cut</a> by more than half this year, putting future advances at risk.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/H7aa5TRQ8fE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Hurricane Irene headed from the Bahamas to North Carolina in 2011.</span></figcaption>
</figure>
<p>Nearly 20 years later, even as the science has progressed, Max Mayfield’s advice is still sound – don’t focus on the skinny black line! Forecasts are uncertain, and an appreciation of that uncertainty is essential to smart decision-making when hurricanes threaten. To help educate users, NHC has established a <a href="http://www.nhc.noaa.gov/verification/">web page dedicated to forecast accuracy</a>. Please drop by and have a look to see how well our forecasts measure up. And finally, even though NOAA and others are expecting a relatively quiet 2015 Atlantic hurricane season, remember: it takes only one bad storm in your neighborhood to make it a bad year for you.</p><img src="https://counter.theconversation.com/content/40794/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Franklin does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Forecasting successes can breed complacency in the general public. But all hurricane damage isn’t necessarily contained within the “cone of uncertainty.”James Franklin, Branch Chief Hurricane Specialist Unit at the National Hurricane Center, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/402132015-04-17T10:13:59Z2015-04-17T10:13:59ZMeasuring coral reef fishes by taking humans out of the picture<figure><img src="https://images.theconversation.com/files/78296/original/image-20150416-5663-1w40pgw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Coral reefs and associated fisheries are of vital social, cultural and economic importance.</span> <span class="attribution"><span class="source">Noah Pomeroy</span>, <span class="license">Author provided</span></span></figcaption></figure><p>We are living in the Anthropocene, a period where humans are the dominant force on Earth’s natural systems. Coral reef ecosystems are no exception. </p>
<p>Widely known for their striking beauty and diversity, coral reefs also have great social, cultural and economic importance. At human-populated islands, small-scale and subsistence coral reef fisheries are often vital sources of protein and income. </p>
<p>However, it is widely recognized that even relatively low levels of fishing can have large impacts on coral reef fish stocks.</p>
<p>How can scientists effectively measure the status and therefore sustainability of coral reef fish populations? One would think that an isolated reef ecosystem shielded from the influence of people would provide an ideal benchmark against which other coral reefs – and their productivity as sources of fish – can be compared. But in a <a href="http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0120516">recent study</a>, we found that it is not that simple.</p>
<p>Using data collected by scientific divers at nearly 2,000 sites at islands and atolls across the western-central Pacific, we developed a method for separating human from other environmental factors to assess reef fish status. We found that not all coral reef areas have the same ability to sustain stocks of fish, and what constitutes “natural” varies substantially among locations.</p>
<h2>Getting a baseline</h2>
<p>A prerequisite for effective coral reef fisheries management is to know how the current status of the ecosystem compares to its ‘pristine’ state. In other words, what would local fish stocks be like if humans had not affected the system at all? For coral reef fisheries, estimating pristine reef fish biomass has been difficult. </p>
<p>Unsurprisingly, where you have <a href="http://dx.doi.org/10.1371/journal.pone.0001548">more humans</a>, you tend to get <a href="http://dx.doi.org/10.1155/2011/826234">fewer</a> <a href="http://www.int-res.com/articles/meps2002/230/m230p253.pdf">fish</a>. Yet to compare a remote reef, distant from human impacts, directly with a populated one can be misleading because it assumes that what is normal or natural for one area applies directly to other areas. Instead, each area is under the influence of environmental factors that operate independently of human influence.</p>
<p>We investigated the relative influence of environmental variation and human impacts on groups of reef fish assemblages. The data set used is a culmination of more than 2,000 hours of underwater visual surveys conducted by NOAA scientists and scuba divers for the <a href="http://www.pifsc.noaa.gov/cred/">Pacific Reef Assessment and Monitoring Program</a> (RAMP).</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/78293/original/image-20150416-30509-twpti5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78293/original/image-20150416-30509-twpti5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78293/original/image-20150416-30509-twpti5.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78293/original/image-20150416-30509-twpti5.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78293/original/image-20150416-30509-twpti5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78293/original/image-20150416-30509-twpti5.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78293/original/image-20150416-30509-twpti5.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">Pacific RAMP divers conducting an underwater visual survey of coral reef fishes.</span>
<span class="attribution"><span class="source">Paula Ayotte</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The Pacific RAMP is one of the world’s largest coral reef monitoring efforts, and it is unique for implementing standardized methods and sending core survey divers throughout coral reefs at nearly 40 US and US-affiliated Pacific islands and atolls. The Pacific RAMP has being monitoring coral reefs of the western central Pacific for 15 years, and scientific scuba divers on the fish team are required to know over 600 species of coral reef fish. Over this period, the fish team has counted and sized <a href="https://pifscblog.wordpress.com/2015/04/09/4999999-fish/">five million coral reef fish</a>! </p>
<p>The islands monitored span a wide range of potential human impact from large population centers, such as Oahu, Maui and Guam, to some of the most remote and pristine coral reefs in the world, including Rose Atoll, the Pacific Remote Islands Marine National Monument and the Northwestern Hawaiian Islands. We paired this unique survey data set with satellite-derived estimates of the environmental conditions at each reef location, including sea surface temperature, wave energy and oceanic productivity – all environmental factors that can influence the composition and abundance of coral reef assemblages.</p>
<p>Consequently, we were able to separate the variability in coral reef fish abundance due to changes in large-scale environmental conditions from human-induced variability. By doing this, we were then able to predict what the fish community would be in the absence of humans. </p>
<h2>Clear human impact</h2>
<p>Consistent with previous findings, we documented sharp declines in reef fish biomass even at very low estimates of human population density. However, the absence of humans from remote, uninhabited reef areas in the Pacific was not always associated with spectacularly high reef fish abundance. Rather, differences were strongly associated with variation in background oceanic productivity.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/78123/original/image-20150415-31660-a5dy2p.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78123/original/image-20150415-31660-a5dy2p.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=451&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78123/original/image-20150415-31660-a5dy2p.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=451&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78123/original/image-20150415-31660-a5dy2p.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=451&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78123/original/image-20150415-31660-a5dy2p.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=567&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78123/original/image-20150415-31660-a5dy2p.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=567&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78123/original/image-20150415-31660-a5dy2p.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=567&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Coral reefs at populated islands (right hand side, with islands order from low to high human population numbers) have fewer coral reef fish than uninhabited and remote areas (left hand side, with islands ordered from high to low oceanic productivity (CHL)). There exists great variability in the expected reef fish biomass by site that is largely due to natural differences in oceanic productivity. The grey bars are predicted fish biomass in the absence of human impacts.</span>
<span class="attribution"><span class="source">williams/plosonepaper</span></span>
</figcaption>
</figure>
<p>Specifically, areas of high oceanic productivity – that is, reefs in areas of upwelling where cooler, nutrient-rich water is drawn up from the deep to these shallow water habitats – had two to four times the biomass observed in less productive areas.</p>
<p>What this means is that no one reef can be assumed the same in its ability to sustain large reef stocks. So using a remote reef in a highly productive region could well be a misleading benchmark toward which fishery managers might strive.</p>
<p>Controlling for the spatial variability in reef fish biomass that is due to locally dependent environmental factors, we then projected what biomass one would expect, given the local context, but in the absence of humans (grey bars in the graph above). The findings were stark, with an estimated 20%-78% reduction in reef fish biomass in the lightly to more densely human populated areas.</p>
<p>The implications of this work are twofold. Firstly, due to the natural variability among this broadly similar habitat type, coral reefs differ in their capacity to sustain a high level of fish biomass, implying that there is no single target for what a healthy reef should look like.</p>
<p>Secondly, our results confirmed that even very low levels of human presence are associated with dramatic declines in reef fish abundance. This suggests that fully protected no-take zones would be necessary to maintain coral reef communities in something that resembles their natural, pristine state. </p>
<p>A related and <a href="http://www.nature.com/nature/journal/v520/n7547/full/nature14358.html">recent global study</a> that also heavily relied upon the Pacific RAMP data concludes that 83% of the world’s reefs have reef fish biomass that is half or less than half of their natural carrying capacity. </p>
<p>This groundbreaking study, the first to provide a global benchmark estimate of pristine fish biomass, estimated a recovery time of between 35 and 60 years if fishing was to stop in areas where it now occurs. For most locations, anything approaching full recovery will require prolonged and effective enforcement of fishery restrictions. </p>
<p>Ultimately, reef fish biomass targets must be a societal rather than scientific choice. These recent studies provide the basis for properly understanding the extent of anthropogenic depletion of coral reef fishes, and as such, they will allow such choices to be made in an informed manner.</p><img src="https://counter.theconversation.com/content/40213/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adel Heenan receives funding from NOAA Coral Reef Conservation Program.</span></em></p><p class="fine-print"><em><span>Ivor D Williams receives funding from the NOAA Coral Reef Conservation Program.</span></em></p>Scuba-diving scientists devise method for gauging the health of coral reefs – a vital ecosystem for keeping fisheries sustainable for people.Adel Heenan, Affiliate researcher, National Oceanic and Atmospheric AdministrationIvor D. Williams, National Oceanic and Atmospheric AdministrationLicensed as Creative Commons – attribution, no derivatives.