Since 1998, bleaching has affected 98% of Australia's Great Barrier Reef, sparing only a small part of the world's largest coral reef, a study published in the journal Current Biology found on Thursday.
Only 2% of this huge underwater ecosystem has escaped the phenomenon since the first major bleaching episode in 1998, the hottest year in history, according to this study.
This record has since been broken several times.
Five episodes of massive bleaching
The frequency, intensity and magnitude of the marine heat waves that cause this bleaching are steadily increasing, says lead author Terry Hughes of the Australian Research Council's (ARC) Center of Excellence for Studies in coral reefs based at James Cook University. “Five episodes of massive bleaching since 1998 have transformed the Great Barrier Reef into a checkerboard of reefs with very different recent histories, ranging from 2% of reefs that have completely escaped bleaching, to 80% that have now significantly bleached at least one. times since 2016, ”he said.
Bleaching is a wasting phenomenon which results in discoloration.
It is due to the increase in the temperature of the water, which causes the expulsion of the symbiotic algae which gives the coral its color and its nutrients.
Listed as World Heritage by Unesco in 1981, the Great Barrier suffered three unprecedented episodes of bleaching during the heatwaves of 2016, 2017 and 2020. Researchers assured in July that the corals had shown signs of healing since the last bleaching while acknowledging that the long-term prospects for this 2,300 km long ecosystem are "very poor".
Reduced resilience of the coral reef
The reef is also threatened by cyclones, more frequent with climate change, and by the purple acanthaster, a coral-eating starfish that has proliferated due to pollution and agricultural runoff. Research released Friday shows that corals already exposed to heat waves are less prone to heat stress, but co-author Sean Connolly, of the Smithsonian Tropical Research Institute, warns that more frequent and greater bleaching reduces the resilience of the Coral reef.
"The coral still needs time to recover before another cycle of heat stress in order to be able to make babies who will disperse, settle in and recover the depleted parts of the reef," he says.
"It is crucial to act to curb climate change".
This study is published as the UN climate summit is being held in Glasgow, Scotland, where Australia, a major exporter of fossil energy, has pledged to achieve carbon neutrality by 2050, refusing to set a more ambitious date of 2030.
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