A study published Thursday reveals that the phenomenon, due to the rise in sea temperature, savings only a tiny part of the largest coral ensemble in the world.
Le Monde
Corals, these vital ocean ecosystems, are irreparably subject to extreme pressure from climate change. A study published Thursday, November 4 reveals that bleaching has received 98% of the Great Coral Barrier, Australian Reef, since 1998, saving an invalid part of the world’s largest coral ensemble. According to the article published In the Current Biology journal , only 2% of this huge submarine ecosystem has escaped the phenomenon from the first major bleaching episode in 1998, the hottest year of history. This record has since been beaten several times.
The frequency, intensity and magnitude of marine heat waves which cause this bleaching continues to rise, underlines the main author, Terry Hughes, Director of the Center of Excellence for Studies on Coral Reefs. James-Cook University, Queensland.
“Five episodes of massive bleaching since 1998 has transformed the Great Coral Barrier into a checkered reef to very different recent stories, ranging from 2% of reefs that have totally escaped 80% whitening which now considerably bleached. Less once since 2016. “
Whitening is a diverse phenomenon that results in discoloration. It is due to the rise in the temperature of the water, it causing the expulsion of the symbiotic algae that give the coral its color and its nutrients. World Heritage by UNESCO in 1981, the Great Barrier suffered three unprecedented bleaching episodes during the 2016, 2017 and 2020 canicles.
This phenomenon, which adds to the acidification of the oceans, has major consequences for ecosystems. Corals, sorts of oasis of ocean deserts, represent only 0.2% of the seamless area, but shelter 30% of known marine biodiversity, to which they provide food sources. They also make many ecosystem services to humans, protecting the coasts against erosion, feeding many populations (fishing, aquaculture) and generating tourism.
“It’s crucial to act. “
In July, the researchers ensured the corals had shown signs of healing since the last bleach while recognizing that the long-term prospects of this ecosystem of 2,300 kilometers long are “very bad”.
Published Thursdays show that corals already exposed to heat waves are less subject to thermal stress, but the coauthor Sean Connolly, from the Smithsonian Tropical Research Institute (Smithsonian Tropical Research Institute), says that a More frequent and more bleaching reduces the resilience of the coral reef. “The coral still needs time to recover before another cycle of thermal stress in order to be able to make babies who will disperse, will settle and recover the reef-up 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 purple acanthaster, a starfish devouring corals that has proliferated due to pollution and agricultural runoff.
This study is published when Glasgow is held in Scotland, the United Nations Climate Summit, where Australia, one of the main fossil energy exporters, is committed to reaching neutrality. Carbon in 2050, refusing to fix the more ambitious date of 2030.