A new episode of mass bleaching of the Great Barrier Reef along Australia's northeast coast, the seventh since 1998, is underway, according to government scientists following 300 aerial surveys shallow reefs.
This phenomenon caused by climate change poses a serious threat to the largest coral reef in the world, which extends more than 2,300 km along the northeast coast of Australia.
A true ecosystem that is home to some 1,500 species of fish and around 4,000 types of molluscs.
Graphic explaining and locating bleaching on the Great Barrier Reef off Australia in 2020. AFP/Adrian LEUNG, John SAEKI, Gal ROMA
“We know that the greatest threat to the world's coral reefs is climate change.
The Great Barrier Reef is no exception,” Environment Minister Tanna Plibersek said in a statement.
And added: “We must act against climate change.
We must protect our exceptional sites and the plants and animals that inhabit them.
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A one degree rise in water temperature
Further studies need to be carried out to assess the severity and extent of bleaching, according to the Australian Coral Reef Authority.
This dieback phenomenon, which results in discoloration, is caused by an increase of just one degree in water temperature which causes the expulsion of symbiotic algae, giving the coral its vibrant color.
However, ocean temperatures along the Great Barrier Reef have reached record levels in recent weeks, according to official data.
According to the head of oceans for WWF Australia, Richard Leck, many corals risk dying if ocean temperatures do not drop quickly in the coming weeks.
“This bleaching event is occurring in an area where corals have never been exposed to these extreme temperatures,” he said.
A global phenomenon
Similar diebacks occurred last year in the northern hemisphere, Leck added, leading to "dramatic" coral losses in Florida and the Caribbean.
Some corals can recover if weather conditions improve, with the exception of those that have significantly bleached or are experiencing repeated heatwaves, scientists say.
But Terry Hughes, one of Australia's leading coral reef scientists, says bleaching events are now so common that reefs are struggling to recover.
In Australia, "the reef is no longer able to achieve the mix of coral species and coral sizes that existed 20 years ago," he said.
“The irony is that the corals that predominate today in most areas of the Great Barrier Reef grow quickly and quickly regain ground, but they are sensitive to heat and will be less tolerant of inevitable next episodes of whitening.
A study in 2022 showed that 98% of the barrier had been affected by bleaching phenomena since 1998.
According to him, heat stress has increased in recent days and is expected to worsen over the next two weeks.
The future of the reef has been a source of tension between the Australian government and UNESCO, which in 2021 threatened to include it on a list of “in danger” world heritage sites.
Such a listing would have been a snub for Australia, dealing a serious blow to the tourist attractiveness of this coral complex which generates $4.8 billion in revenue.
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Behind-the-scenes diplomatic negotiations and fierce lobbying by Australia have so far prevented the reef from being included on this list.
In 2022, a $700 million program over nine years to protect the Great Barrier Reef was announced by the Australian government.
Already in 2015, when the UN threatened to downgrade the status of the Great Barrier, listed as a world heritage site since 1981, Australia had already launched a multi-billion dollar investment plan to combat the deterioration of the reef.