Corals: in Australia, bleaching reached 98% of the Great Reef

Corals, these vital ocean ecosystems, are irreparably under the extreme pressure of climate change. A study published Thursday, November 4 reveals that bleaching has affected 98% of the Great Barrier Reef, Australian reef, since 1998, sparing a crippled part of the largest coral reef in the world. According to the published article in the review Current Biology, only 2% of this immense underwater ecosystem has escaped the phenomenon since the first major bleaching episode in 1998.

The frequency, intensity and magnitude of the marine heat waves that cause this bleaching are on the rise, says lead author Terry Hughes, director of the university’s Center of Excellence for Coral Reef Studies James-Cook, Queensland.

“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 once. since 2016. “

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 heat waves of 2016, 2017 and 2020.

This phenomenon, which is added to the acidification of the oceans, has major consequences for ecosystems. Corals, a kind of oasis in oceanic deserts, represent only 0.2% of the sea surface, but are home to 30% of known marine biodiversity, for which they provide sources of food. They also provide many ecosystem services to humans, protecting coasts against erosion, feeding many populations (fishing, aquaculture) and generating tourism.

Story: Corals: bleaching episodes have increased tenfold since the 1980s

“It is crucial to act”

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-kilometer-long ecosystem are “Very bad”.

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 says more frequent bleaching and more importantly 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 that will disperse, settle and recover the depleted parts of the reef.”, he explains. “It is crucial to act to curb climate change. “

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.

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The study is published as the United Nations 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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The World with AFP

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Corals: in Australia, bleaching reached 98% of the Great Reef