The Great Barrier Reef, northeast of Australia, is currently experiencing the worst bleaching episode ever observed, under the effect of global warming, with 73% of its reefs damaged, the authority which manages it announced on Wednesday .
“The cumulative impact suffered by the barrier this summer was higher than in previous summers,” said the Great Barrier Marine Park Authority, which depends on the Australian federal government, in a press release.
Announced in March, this new episode of massive bleaching, due to rising water temperatures, is the fifth in eight years. This decline phenomenon threatens the survival of coral reefs in all four corners of the world, including the Great Reef, also alerted the American Oceanic and Atmospheric Observation Agency (NOAA) on Monday.
The Great Barrier Reef, which stretches 2,300 km along the coast of the state of Queensland, is often considered the largest living structure in the world. It is home to extremely rich biodiversity, with more than 600 species of coral and 1,625 species of fish.
Aerial observations showed that around 730 of the more than 1,000 reefs observed had bleached, the Marine Park Authority said on Wednesday.
This phenomenon is caused by an increase in water temperature which causes the expulsion of symbiotic algae giving the coral its bright color. If high temperatures persist, the coral turns white and dies.
A “difficult” summer
In several regions of the marine park, “the corals were exposed to record levels of heat”, underlines the Authority, which notes that the austral summer of 2023-2024 was the second hottest ever observed in the region.
“The Great Barrier Reef is an incredible ecosystem, and although it has shown its resilience time and time again, this summer has been particularly challenging,” said Roger Beeden, the Marine Park Authority’s chief scientist.
Another government report says up to 46% of reefs experienced record heat stress, while in 2016 only 20% of reefs were exposed.
“This is the most serious event that the south of the reef has experienced,” Richard Leck, head of oceans at WWF Australia, told AFP, deeming it “scary” that bleaching is “more widespread” in areas hitherto spared.
“Immediate measures”
“We risk losing irreplaceable ecosystems forever if we do not take immediate action to reduce global emissions,” warned Anna Marsden, director of the Great Barrier Reef Foundation.
During a recent mission to the Great Barrier Reef, AFP journalists visited one of the areas most affected by the phenomenon.
Lizard Island, a little slice of tropical paradise off the northeastern tip of Australia, would normally be teeming with thriving coral life. But today, it is nothing more than a marine cemetery. Around 80% of the reef has bleached this summer and many of the affected corals will struggle to survive.
Marine biologist Anne Hoggett has lived and worked on Lizard Island for 33 years. She says that when she arrived, coral bleaching only happened about every ten years. Today, it occurs every year, in varying proportions.
“We don’t know yet whether they’ve already suffered too much damage to recover or not,” she said.
Not confined to Australia
According to Mr. Leck of WWF, “we will not know for a few months” what “coral mortality” will be.
Australia has invested some 5 billion Australian dollars (3 billion euros) to improve water quality, reduce the effects of climate change and protect endangered species.
Thanks to these investments, in August 2023 UNESCO temporarily decided not to include the Great Barrier on the list of world heritage in danger, as it had been threatening to do since 2021.
But Australia is also one of the largest emitters of greenhouse gases, one of the largest exporters of natural gas and coal, and has only very recently set targets, considered unambitious, to achieve carbon neutrality.
As NOAA announced, the phenomenon is not confined to Australia: the American agency announced that the planet was experiencing its second largest episode of coral bleaching in ten years.
“Coral bleaching is becoming more and more frequent and serious,” noted Derek Manzello, coordinator of the NOAA Coral Reef Observatory, pointing to record ocean temperatures.
NOAA estimates that the planet has already lost 30 to 50% of its coral reefs and that these could, without major changes, completely disappear by the end of the century.