Scientists say the latest study of the effects of a heatwave on a part of the Great Barrier Reef shows 'catastrophic' damage – with global warming no longer a projection but an immediate reality and urgent action necessary.
Michael Kingsford is a Distinguished Professor of Marine Biology at James Cook University's College of Science and Engineering. Along with University of Sydney scientists he tracked the health of 462 coral colonies near One Tree Island in the southern Great Barrier Reef during a heatwave.
"The 2023- 2024 marine heatwave was extreme in triggering coral bleaching and high mortality. We tracked the colonies over 161 days in 2024 from the heatwave peak through autumn and winter cooling," said Professor Kingsford.
He said in February 66% of the colonies were bleached, rising to 80% by April.
"By May, 44% of the bleached colonies were dead and 53% in July. Across that month, 31% of colonies remained bleached and 16% recovered," said Professor Kingsford.
He said the 2024 event was the seventh mass bleaching event on the GBR since 1998 and the fifth since 2016, and it brought severe conditions and rapid coral health decline not previously seen in the southern GBR region.
"As corals can recover from mild bleaching when water cools, there is a perception that while bleaching is bad, it's not necessarily catastrophic.
"What we saw at One Tree Reef was catastrophic. Rapid high mortality left no opportunity for these corals to recover, some coral even turned to rubble," said Professor Kingsford.
He said despite the reef being heavily protected for 50 years as a designated Scientific Zone with limited public access, this was no defence.
"While protection from disturbances caused by humans can enhance prospects for coral survival during heatwaves, the protected status and offshore location did not guard One Tree Reef from bleaching and mortality," said Professor Kingsford.
He said mass coral bleaching is a global phenomenon and is now starting to be seen every two years on the GBR.
"Catastrophic conditions and dire ecosystem changes are no longer a threat on a distant horizon. It's happening now. Our findings reinforce the need for urgent global action, immediately, on ambitious climate and reduced emissions targets."
