Coral bleaching occurs when a disturbance—in this case unusually warm waters due to El Niño—causes corals to lose their color. The bright organisms can recover under the right conditions, but bleaching events typically lead some to die. More that two-thirds of corals in the northern part of the reef closest to shore, the most affected region, have died in the last nine months, researchers said. Around a quarter died farther offshore in the north.
"The coral is essentially cooked," James Cook University researcher Andrew Baird, who participated in the survey, told Reuters.
The Great Barrier Reef, perhaps the world's best known coral reef, is far from the only region hit hard by this year's bleaching. Researchers from the National Oceanic and Atmospheric Administration (NOAA) reported earlier this year that bleaching had occurred in a greater area than ever before, stretching from the South Pacific to the Caribbean.
Coral reefs play a key role in marine ecosystems, providing a habitat for fish, and serve as an important barrier protecting coastal communities from storms and extreme weather events. They also contribute billions to local economies through tourism and fishing. Tourism connected to the Great Barrier Reef alone employs 70,000 people and generates $5 billion in revenue annually.
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Restoring coral reefs is a tall order in a warming climate. Scientists expect bleaching to get more frequent and more severe, even if the world fulfills commitments to limit climate change. And, once reefs are gone, they will not come back.
“If you think of corals as canaries [in a coal mine], they’re chirping really loudly right now,” said Jennifer Koss, NOAA’s Coral Reef Conservation Program director, earlier this year. “The ones that are still alive, that is.