Robust Great Barrier Reef holds its own despite heavy toll on coral cover
Bleaching, cyclones, and the crown-of-thorns starfish have seen our Great Barrier Reef’s hard coral cover decline, but it’s holding it’s own against other reefs around the world.
The Great Barrier Reef has suffered the largest annual declines in hard coral after being hit by the summer’s cyclones and widespread bleaching — but still has near long-term average coverage and is in better condition than many other reefs around the world.
The annual monitoring survey results by the Australian Institute of Marine Science has revealed that four-decade high levels of coral coverage recorded in the past three years has been depleted at either end of the 2300km-long reef.
Record declines in coral have been found in two of the reef’s three regions: the northern stretch that runs from off Cooktown to the tip of Cape York, which suffered a 24.8 per cent loss in coverage to 30 per cent, and the southern end, running from off Proserpine down to Gladstone, which lost 30.6 per cent to 26.9 per cent of coral coverage.
The central region, which runs from off Cooktown to Proserpine, lost 13.9 per cent to 28.6 per cent.
The AIMS’s long-term monitoring program has been going for 39 years and is regarded as a rigorous and comprehensive survey of the reef’s health.
A total of 124 coral reefs were surveyed; with two reefs found to have 75 per cent coral coverage and two with less than 10 per cent.
A third of the reefs had hard coral cover of between 30 per cent and 50 per cent.
The declines have been blamed on “climate change-induced heat stress” causing a mass coral bleaching event last year – its fifth since 2016 – and a number of other major stresses on the reef.
“The summer of 2024 brought multiple stressors to the GBR including cyclones, flooding and crown-of-thorns starfish, but the mass coral bleaching event was the primary source of coral mortality,’’ the report said.
“In 2025, hard coral cover declined substantially across the GBR, although considerable coral cover remains in all three regions.”
AIMS lead researcher Mike Emslie said the results showed there was an “increased volatility” in the coral coverage and that the declines in the past year had been mitigated by record levels before the bleaching. “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 in a relatively short amount of time, where previously such fluctuations were moderate.
“Coral cover now sits near the long-term average in each region,” Dr Emslie said.
The report said last year’s bleaching event was a global phenomenon first detected in the northern hemisphere in 2023.
It found the mass bleaching had the “largest spatial footprint” of any previous event, and was observed in all three regions.
But the report said the Great Barrier Reef comparatively “currently retains higher coral cover than many reefs globally.”
“Coral bleaching levels and mortality during this ongoing global event have been more severe in other parts of the world, such as the Caribbean, where mortality was high on almost all reefs and very little coral currently remains,’’ the report said.
Overall, 48 per cent of surveyed reefs “underwent a decline in percentage coral cover, 42 per cent showed no net change, and only 10 per cent had an increase”.
Dr Emslie said the fast-growing “Acropora corals,” which helped facilitate the rapid recovery observed across many reefs between 2017 and 2024, were among the corals with high mortality from the bleaching event.
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