Editor\u2019s note: From \u201cblue carbon\u201d to \u201cecosystem services,\u201d environmental jargon is everywhere. Conservation International looks to make sense of it in an explainer series we\u2019re calling \u201cWhat on Earth?”<\/em><\/p>\n In this installment, we explore coral bleaching, a crisis impacting the world\u2019s reefs.<\/em><\/span><\/p>\n Climate change is happening. And it\u2019s placing the world\u2019s reefs in peril.<\/span><\/p>\n In Western Australia, scientists recently reported the worst coral bleaching ever seen, with some reefs losing up to 90 percent<\/a> of their coral after a long, intense marine heatwave. At the same time, the Great Barrier Reef suffered its sharpest coral decline<\/a> in nearly 40 years, as once-colorful corals turned white and brittle. These disasters are part of a global bleaching crisis that has now affected more than 80 percent<\/a> of reefs around the world.<\/span><\/p>\n Well, remember, corals aren\u2019t just colorful rocks \u2014 they\u2019re living things, made of hundreds or thousands of individual animals called polyps. Each polyp is only a few millimeters across and is shaped a bit like a miniature sea anemone.<\/span><\/p>\n Like most animals, they\u2019re sensitive to big temperature swings. But there\u2019s a strange twist behind the bleaching: Polyps host even tinier<\/em> organisms inside them \u2014 microscopic algae that use sunlight to make food. The algae feed the corals, while the corals give the algae nutrients and shelter.<\/span><\/p>\n But when the ocean gets too hot, the coral becomes stressed and ejects the algae<\/a>. Without the algae, the coral turns ghostly white \u2014 i.e. bleaching. If the heat lasts too long, the coral starves and dies.<\/span><\/p>\n Dead coral in the Pacific Ocean.<\/em><\/p>\n When a coral bleaches, the polyps inside are either starving or already dead. What\u2019s left behind is a kind of skeleton \u2014 the stony structures it built while alive. At first glance, a tourist visiting a famous reef may not even notice the difference, with all the branching structures still in place. But without the living coral, it\u2019s a graveyard.<\/span><\/p>\n When reefs crumble, vibrant ecosystems vanish with them.<\/span><\/p>\n In their healthy state, reefs are absolutely teeming with life. Scientists estimate that a quarter<\/a> of all marine species depend on reefs at some point in their lives \u2014 from schools of colorful fish to vibrant invertebrates, sea turtles, eels, sharks and mantas.<\/span><\/p>\n Take the reef away, and you lose that abundance. That\u2019s bad for nature, but it\u2019s also bad for people.<\/span><\/p>\n Coral reefs support a diversity of marine life.<\/em><\/p>\n What do coral reefs have to do with people?<\/strong><\/p>\n A lot, actually. For one thing, reefs support fisheries that feed hundreds of millions of people<\/a> around the world. Many coastal communities rely on reef fish as their main source of protein.<\/span><\/p>\n Reefs also act like natural seawalls. Their limestone structures break up waves before they hit the shore, helping to protect coastlines from erosion and storm surges. Without them, coastal flooding would be far worse.<\/span><\/p>\n Look, it\u2019s simple: we have to stop heating the planet.<\/span><\/p>\n Even a small rise in the Earth\u2019s average temperature makes the oceans much hotter, pushing corals past their limit. Scientists say that in a world warmed by about 1.5 degrees Celsius (nearly 3 degrees Fahrenheit), some reefs might still survive. But at 2 degrees \u2014 just a little hotter \u2014 99 percent of reefs would likely die off<\/a>.<\/span><\/p>\n Even a small increase in temperature can be catastrophic for coral reefs.<\/em><\/p>\n It\u2019s heartbreaking, but yes.<\/span><\/p>\n Corals living deeper in the ocean, at cooler depths, are definitely far less likely to bleach than those along the coast. However, they aren\u2019t immune to it<\/a> and (sorry, more bad news here) they face other urgent threats, like deep-sea mining<\/a>.<\/span><\/p>\n While remote reefs look very different from their colorful shallow-water counterparts, they are still critical refuges for marine life.<\/span><\/p>\n In 2024, a Conservation International-funded deep-sea expedition<\/a> off the coasts of Chile and Peru uncovered a treasure trove of biodiversity (including more than 100 species likely new to science). It\u2019s just one of the many deep sea, coral-laden ecosystems rarely glimpsed by humans \u2014 but potentially threatened by heat stress and mining.<\/span><\/p>\n For years, <\/span>Conservation International advocated for the recently ratified\u00a0high seas treaty<\/a>, which will help establish new marine protected areas to shield international waters \u2014 and the corals they house \u2014 from increasing threats.<\/span><\/p>\n![\"\"\/](\"https:\/\/cicloud.imgix.net\/images\/default-source\/vault-images-s3\/ci_51154529_full.jpg?sfvrsn=db2fd521_3&&auto=compress&auto=format&fit=crop?&auto=compress&auto=format&w=800\")
\u00a9 Keith A. Ellenbogen<\/span><\/p>\n![\"\"\/](\"https:\/\/ciorg.imgix.net\/images\/default-source\/default-album\/ci_360048696aa4db3d-4d4e-4268-83fa-d1fff3e2e01b?&auto=compress&auto=format&fit=crop?&auto=compress&auto=format&w=800\")
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