What’s Happening?
The Great Barrier Reef has suffered its most widespread and severe coral bleaching event since monitoring began 39 years ago, according to the Australian Institute of Marine Science (AIMS). The findings come from AIMS’ 2025 Long-Term Monitoring Program (LTMP), which surveyed 124 reefs between August 2024 and May 2025.
Hard coral cover declined across all three reef regions. For the first time, the southern region recorded its largest annual loss. The 2024 mass bleaching was the main driver, with additional pressure from cyclones and crown-of-thorns starfish.
Why It Matters
The Reef’s condition reflects broader ocean health. “Mass bleaching events are becoming more intense and are occurring with more frequency,” said AIMS CEO Professor Selina Stead. “This was the second time in a decade that the Reef experienced mass bleaching in two consecutive years.”
She added that the 2024 bleaching event affected almost all coral reefs in Australia. “Western Australian reefs also experienced the worst heat stress on record. It’s the first time we’ve seen a single bleaching event affect almost all the coral reefs in Australia.”
Local Impact
Bleaching stretched from Cape York to Gladstone. The fast-growing Acropora corals were among the worst affected due to their sensitivity to heat, cyclones and crown-of-thorns starfish.
“These corals are the fastest to grow and the first to go,” said AIMS LTMP leader Dr Mike Emslie. “This year’s results illustrate that.” He also confirmed that this was the first time the southern region recorded substantial bleaching impacts, resulting in its largest annual decline since monitoring began.
By the Numbers
Hard coral cover dropped significantly across all regions:
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Southern region (Proserpine to Gladstone): 38.9% to 26.9%
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Northern region (Cape York to Cooktown): 39.8% to 30%
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Central region (Cooktown to Proserpine): 33.2% to 28.6%
Dr Emslie said the recent high coral cover helped buffer the impact. “This year’s record losses in hard coral cover came off a high base, thanks to the record high of recent years.”
Zoom In
Out of the 124 reefs surveyed:
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77 reefs had coral cover between 10% and 30%
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33 reefs had between 30% and 50%
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2 reefs had more than 75%
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2 reefs had less than 10%
“We are now seeing increased volatility in the levels of hard coral cover,” said Dr Emslie. “This is a phenomenon that emerged over the last 15 years and points to an ecosystem under stress.” He noted that coral cover now sits near the long-term average in each region, with faster shifts between highs and lows than seen in the past.
Zoom Out
The 2024 mass bleaching was part of a global event that began in the Northern Hemisphere in 2023. It was the fifth mass bleaching on the Great Barrier Reef since 2016 and had the largest spatial footprint recorded.
“These results provide strong evidence that ocean warming, caused by climate change, continues to drive substantial and rapid impacts to Reef coral communities,” said Professor Stead.
About the LTMP
The AIMS Long-Term Monitoring Program tracks coral health by assessing hard coral cover on reefs across the Great Barrier Reef. Scientists use manta tow surveys and fixed site observations to measure coral cover, coral types, fish populations, and causes of coral death such as bleaching, disease and starfish outbreaks.
The 2024 mass bleaching event prompted extra in-water surveys, which confirmed and validated the data from the manta tows.
What to Look For Next
AIMS calls for stronger climate action, including reductions in greenhouse gas emissions and improved local reef management strategies.
