Great Barrier Reef suffers record coral decline, mass bleaching
The Great Barrier Reef last year suffered the largest annual decline in coral cover in two of the three regions regularly surveyed since monitoring began 39 years ago due to climate change-induced heat stress causing mass bleaching.
From Cape York to Cooktown, known as the northern region by the Australian Institute of Marine Science, which leads long-term monitoring of the reef, coral cover fell by a quarter from 39.8 per cent to 30 per cent.
Sections of the Great Barrier Reef suffered their largest annual decline in coral cover due to bleaching during 2024. Credit: © AIMS | LTMP
In the central region, from Cooktown to Proserpine, it fell from 33.2 per cent to 28.6 per cent, and in the southern region, which extends to Gladstone, it was down almost a third, or 38.9 per cent to 26.9 per cent, says the AIMS report, which was released overnight.
But because these sections of the reef had relatively high levels of coverage before the 2024 marine heatwave took hold, the impact was partially cushioned, said Dr Mike Emslie, who leads the long-term monitoring project.
“This year’s record losses in hard coral cover came off a high base, thanks to the record high of recent years,” he said.
“We are now seeing increased volatility in the levels of hard coral cover. This is a phenomenon that emerged over the last 15 years and points to an ecosystem under stress.
“We have seen coral cover oscillate between record lows and record highs,” he said.
Coral bleaching, once a rare event, has hit sections of the Great Barrier Reef in 1998, 2002, 2016, 2017, 2020, 2022, 2024 and 2025.
Outbreaks of crown of thorn starfish have compounded damage to the reef caused by climate change.Credit: © AIMS | LTMP
Richard Leck, head of Oceans for the World Wide Fund for Nature Australia, said the devastating coral mortality intensifies the focus on Australia’s 2035 emissions reduction target, due to be announced soon.
“In one fell swoop, climate change wiped out the encouraging coral recovery of recent years.
Illustration by Matt Golding
“The Australian government can show it’s determined to give the reef a fighting chance by announcing a strong 2035 target backed by policies to deliver big emissions reductions.”
According to the AIMS report, the reef has also been battered by cyclones and outbreaks of the crown of thorns starfish. The relatively high levels of coral coverage before the 2024 and 2025 events had occurred because damage and mortality from bleaching in 2020 and 2022 had been limited, giving the reef years to recover between larger bleaching events in 2017 and 2024.
The danger faced by the Great Barrier Reef is that as sea surface temperatures keep getting hotter due to the world’s failure to arrest greenhouse gas pollution, the reef is getting less time to recover between the heatwaves.
“You’d have to think that once we’re hitting 2 degrees [of warming], the thermal tolerance of corals will be surpassed because we’re at 1.5 [degrees] now, and we’re seeing bleaching almost every summer that’s come in the last five or six years,” said Emslie.
“So pushing it another half degree, I would suggest, we’ll push a lot of these corals past their thermal tolerance,” he said.
Leck said that to give the reef a fighting chance, the federal government should announce an ambitious greenhouse gas reduction target for 2035 under the Paris Agreement. That target is now being considered by the Climate Change Authority, which is expected to give advice on the target to the government over the coming weeks.
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