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It’s possible the overall percentage of reefs experiencing heat stress may soon pass a record
First around Fiji, then the Florida Keys, then Australia’s Great Barrier Reef, and now in the Indian Ocean. In the past year, anomalous ocean temperatures have left a trail of devastation for the world’s corals, bleaching entire reefs and threatening widespread coral mortality — and now, scientists with the National Oceanic and Atmospheric Administration and International Coral Reef Initiative say the world is experiencing its fourth global bleaching event, the second in the last decade.
At least 53 countries and local regions have experienced mass bleaching across the Atlantic, Pacific and Indian oceans. Bleaching — which occurs when stressed coral turn white after expelling symbiotic algae that provide food and color — must be confirmed within each ocean basin to be declared a global bleaching event.
Derek Manzello, an ecologist and head of NOAA’s Coral Reef Watch program, said the frequency and severity of bleaching events has increased since the early 1980s. That intensity and regularity has also ramped up in the last two decades.
“Now we’re just reaching a point in this warming cycle where these events are becoming so extreme and they’re just getting worse and worse and worse,” Manzello said.
According to the Global Bleaching Event Index, which is based on sea surface temperatures data, more than 54 percent of all the reef areas on the planet have experienced bleaching-level heat stress in the past 365 days. And that number is increasing by 1 percent each week, Manzello said. For context, during the worst global coral bleaching event on record between 2014 and 2017, the Global Bleaching Event Index peaked at 56 percent.
“Right now, we’re almost equal with the worst global bleaching event on record in terms of spatial extent,” Manzello said. It’s possible the overall percentage of reefs experiencing heat stress will surpass the previous record in the next few weeks.
“This should be a global wake-up call. The fact that corals are bleaching in each ocean basin essentially simultaneously,” Manzello said. “And more than half the reefs on the planet have basically experienced bleaching-level heat stress in the last year…”
