Since 1998, bleaching has affected 98% of Australia’s Great Barrier Reef, only a small part of the world’s largest coral reef,
A study published this Thursday in the journal Current Biology reveals.

According to this study, only 2% of this vast underwater ecosystem has survived the event since the first major bleaching episode, the hottest year in history, in 1998. Since then this record has been broken several times.

Five episodes of massive bleaching

Lead author Terry Hughes, from the Australian Research Council’s (ARC) Center of Excellence for Studies in Coral Reefs at James Cook University, says the ocean heat waves that cause this bleaching are increasing in frequency, intensity and magnitude. “Five episodes of massive bleaching since 1998 have turned the Great Barrier Reef into a checkerboard of reefs with very different recent histories, ranging from 2% of reefs that have survived bleaching entirely, to 80% Till now which have bleached significantly at least once. Bar. Since 2016,” he said.

Bleaching is a wasting phenomenon that results in discoloration. This is caused by an increase in water temperature, which causes the expulsion of the symbiotic algae that give coral its color and its nutrients. Listed as a World Heritage Site by UNESCO in 1981, the Great Barrier suffered three unprecedented episodes of bleaching during the heatwaves of 2016, 2017 and 2020. The researchers assured in July that the corals had shown signs of healing since the last bleaching, while acknowledging that the prospects for this long 2,300 km long ecosystem are “very poor”.

low resilience of coral reefs

The reef is also threatened by cyclones, more frequently with climate change, and by the purple acanthaster, a coral-eating starfish that has increased due to pollution and agricultural runoff. Research released Friday suggests corals already exposed to heat waves are less prone to heat stress, but co-author Sean Connolly of the Smithsonian Tropical Research Institute warned that more frequent Excess bleaching reduces the resilience of coral reefs.

“The coral still needs time to recover before another cycle of heat stress to be able to produce babies, which will be able to disperse, settle and recover from the bad parts of the reef,” they said. it is said. “It is important to act to stop climate change”. The study is published as the United Nations Climate Summit in Glasgow, Scotland, where Australia, a major exporter of fossil energy has pledged to achieve carbon neutrality by 2050, declined to set a more ambitious date of 2030 Is.