Bleaching has affected 98% of Australia’s Great Barrier Reef since 1998, sparing a tiny fraction of the world’s largest coral reef, a study released Thursday revealed.
According to the article in the journal Current Biology, only 2% of this huge underwater ecosystem has escaped the phenomenon since the first major bleaching episode in 1998, the hottest year in history. This record has since been broken several times.
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 significantly bleached at least once. 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 outlook for this 2300 km long ecosystem is “very poor”.
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 Thursday shows 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 so that it can have babies that will disperse, settle in and cover the depleted parts of the reef,” he says.
“It is crucial to act to curb climate change”.
The study is published as the UN climate summit COP26 is taking place in Glasgow, Scotland, and Australia, a leading fossil energy exporter, has pledged to achieve carbon neutrality by 2050. , refusing to set a more ambitious date of 2030.