The Chagos Archipelago<\/a> is one of the most remote, seemingly idyllic places on Earth. Coconut-covered sandy beaches with incredible bird life rim tropical islands in the Indian Ocean, hundreds of miles from any continent. Just below the waves, coral reefs stretch for miles along an underwater mountain chain<\/a>.<\/p>\n\n\n\n It\u2019s a paradise. At least it was before the heat wave.<\/p>\n\n\n\n When I first explored the Chagos Archipelago 15 years ago, the underwater view was incredible. Schools of brilliantly colored fish in blues, yellows and oranges darted among the corals of a vast, healthy reef system. Sharks and other large predators swam overhead. Because the archipelago is so remote and sits in one of the largest marine protected areas<\/a> on the planet, it has been sheltered from industrial fishing fleets and other activities that can harm the coastal environment.<\/p>\n\n\n\n But it can\u2019t be protected from climate change.<\/p>\n\n\n\n In 2015, a marine heat wave struck, harming coral reefs worldwide. I\u2019m a marine biologist<\/a> at the University of Miami\u2019s Rosenstiel School of Marine and Atmospheric Science, and I was with a team of researchers on a 10-year global expedition to map the world\u2019s reefs<\/a>, led by the Khaled bin Sultan Living Oceans Foundation<\/a>. We were wrapping up our work in the Chagos Archipelago at the time. Our report on the state of the reefs there was just published<\/a> in spring 2021.<\/p>\n\n\n\n As the water temperature rose, the corals began to bleach. To the untrained eye, the scene would have looked fantastic. When the water heats up, corals become stressed and they expel the tiny algae called dinoflagellates that live in their tissue. Bleaching isn\u2019t as simple as going from a living coral to a bleached white one, though. After they expel the algae, the corals turn fluorescent pinks and blues and yellows as they produce chemicals to protect themselves from the Sun\u2019s harmful rays<\/a>. The entire reef was turning psychedelic colors.<\/p>\n\n\n\n That explosion of color is rare, and it doesn\u2019t last long. Over the following week, we watched the corals turn white and start to die. It wasn\u2019t just small pieces of the reef that were bleaching \u2013 it was happening across hundreds of square miles.<\/p>\n\n\n\n What most people think of as a coral is actually many tiny colonial polyps that build calcium carbonate skeletons. With their algae gone, the coral polyps could still feed by plucking morsels out of the water, but their metabolism slows without the algae, which provide more nutrients through photosynthesis<\/a>. They were left desperately weakened and more vulnerable to diseases. We could see diseases taking hold, and that\u2019s what finished them off.<\/p>\n\n\n\n We were witnessing the death of a reef.<\/p>\n\n\n\n The devastation of the Chagos Reef wasn\u2019t happening in isolation.<\/p>\n\n\n\n Over the past century, sea surface temperatures<\/a> have risen by an average of about 0.13 degrees Celsius<\/a> (0.23 F) per decade as the oceans absorb the vast majority of greenhouse gas emissions from human activities, largely from the burning of fossil fuels. The temperature increase and changing ocean chemistry affects sea life of all kinds, from deteriorating the shells of oysters and tiny pteropods<\/a>, an essential part of the food chain, to causing fish populations to migrate to cooler water.<\/p>\n\n\n\n Corals can become stressed when temperatures around them rise just 1 C<\/a> (1.8 F) above their tolerance level. With water temperature elevated from global warming, even a minor heat wave can become devastating. https:\/\/www.youtube.com\/embed\/IEWJAEkGeNk?wmode=transparent&start=0<\/p>\n\n\n\n In 2015, the ocean heat from a strong El Ni\u00f1o<\/a> event triggered the mass bleaching in the Chagos reefs and around the world<\/a>. It was the third global bleaching on record, following events in 1998<\/a> and 2010<\/a>.<\/p>\n\n\n\n Bleaching doesn\u2019t just affect the corals \u2013 entire reef systems and the fish that feed, spawn and live among the coral branches suffer. One study of reefs<\/a> around Papua New Guinea in the southwest Pacific found that about 75% of the reef fish species declined after the 1998 bleaching, and many of those species declined by more than half.<\/p>\n\n\n\n Research shows marine heat waves are now about 20 times more likely<\/a> than they were just four decades ago, and they tend to be hotter and last longer. We\u2019re at the point now that some places in the world are anticipating coral bleaching every couple of years.<\/p>\n\n\n\n That increasing frequency of heat waves is a death knell for reefs. They don\u2019t have time to recover before they get hit again.<\/p>\n\n\n\n![\"A](\"https:\/\/images.theconversation.com\/files\/397204\/original\/file-20210426-15-ng6gsy.jpg?ixlib=rb-1.1.0&rect=480%2C586%2C1097%2C689&q=45&auto=format&w=754&fit=clip\")
![\"Two](\"https:\/\/images.theconversation.com\/files\/397178\/original\/file-20210426-13-v15dqm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip\")
<\/a>Rising temperatures increase the heat wave risk<\/h2>\n\n\n\n
![Chagos Archipelago<\/a> is one of the most remote, seemingly idyllic places on Earth. Coconut-covered sandy beaches with incredible bird life rim tropical islands in the Indian Ocean, hundreds of miles from any continent. Just below the waves, coral reefs stretch for miles along an](\"https:\/\/en.wikipedia.org\/wiki\/Chagos_Archipelago#\/media\/File:Chagos_map.PNG\"){kind=link}