Watching Remote Chagos Reef Die: A Final Explosion Of Color Before Final Bleaching Takes Hold
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In 2015, a marine heat wave struck, harming coral reefs worldwide. I’m a marine biologist at the University of Miami’s 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’s reefs, led by the Khaled bin Sultan Living Oceans Foundation. 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 in spring 2021.
As the water temperature rose, the corals began to bleach. To the untrained eye, the scene would have looked fantastic. When the water heats up, corals become stressed and they expel the tiny algae called dinoflagellates that live in their tissue. Bleaching isn’t as simple as going from a living coral to a bleached white one, though. After they expel the algae, the corals turn fluorescent pinks and blues and yellows as they produce chemicals to protect themselves from the Sun’s harmful rays. The entire reef was turning psychedelic colors.
Just before they turned white, the corals turned abnormally bright shades. Photo: Phil Renaud/Khaled bin Sultan Living Oceans Foundation
That explosion of color is rare, and it doesn’t last long. Over the following week, we watched the corals turn white and start to die. It wasn’t just small pieces of the reef that were bleaching – it was happening across hundreds of square miles. What most people think of as a coral reef 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. They were left desperately weakened and more vulnerable to diseases. We could see diseases taking hold, and that’s what finished them off. We were witnessing the death of a reef.
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During the Global Reef Expedition, we visited over 1,000 reefs around the world. Our mission was to conduct standardized surveys to assess the state of the reefs. We also mapped the reefs in detail so scientists could document and hopefully respond to changes in the future. With that knowledge, countries can plan more effectively to protect the reefs, important national resources, providing hundreds of billions of dollars a year in economic value while also protecting coastlines from waves and storms. We saw damage almost everywhere, from the Bahamas to the Great Barrier Reef. Some reefs are able to survive heat waves better than others. Cooler, stronger currents, and even storms and cloudier areas can help prevent heat building up. But the global trend is not promising. The world has already lost 30 percent to 50 percent of its reefs in the last 40 years. Scientists have warned that most of the remaining reefs could be gone within decades.
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https://www.theinertia.com/environment/coral-reef-bleaching-witness-death-from-rising-sea-temperatures/