What’s Happening?
The Great Barrier Reef has suffered one of its most severe annual declines in hard coral cover in nearly four decades, according to the Australian Institute of Marine Science (AIMS) 2025 Long-Term Monitoring Program (LTMP) report. The drop follows the 2024 mass bleaching event, intensified by climate change, cyclones, and outbreaks of crown-of-thorns starfish.
Why It Matters
This year marks the most widespread bleaching event on record across all three regions of the Reef. Scientists are warning that the system is now more volatile, with coral cover swinging between highs and lows in shorter cycles.
AIMS CEO Professor Selina Stead said, “Mass bleaching events are becoming more intense and are occurring with more frequency… This was the second time in a decade that the Reef experienced mass bleaching in two consecutive years.”
Local Impact
The impact is being felt across the entire Reef, from Cape York to Gladstone. Notably, the southern region experienced substantial bleaching impacts for the first time since monitoring began, a worrying sign of the expanding threat.
By the Numbers:
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Hard coral cover declined by 25% in the northern region (from 39.8% to 30%)
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13.9% drop in the central region (from 33.2% to 28.6%)
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Almost one-third loss in the southern region, falling from 38.9% to 26.9%
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124 reefs surveyed, with most (77) showing coral cover between 10% and 30%
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Only two reefs had coral cover above 75%, while another two fell below 10%
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This was the fifth mass bleaching since 2016, and the second back-to-back bleaching year in a decade
Zoom In
LTMP leader Dr Mike Emslie said coral species like Acropora are particularly vulnerable: “These corals are the fastest to grow and the first to go. They are susceptible to heat stress, cyclones, and are a favourite food of crown-of-thorns starfish.” He added that the Reef now shows a pattern of “increased volatility in hard coral cover,” highlighting the ecosystem’s fragility.
Zoom Out
This year’s mass bleaching event was part of a global phenomenon that began in 2023 and is the first to affect nearly all of Australia’s coral reefs. “Western Australian reefs also experienced the worst heat stress on record,” said Professor Stead. “It’s the first time we’ve seen a single bleaching event affect almost all the coral reefs in Australia.”
What To Look For Next
AIMS will continue detailed reef surveys and share findings through peer-reviewed research. The results underscore the need for strong global action on emissions, better reef management, and support for reef adaptation efforts. As Professor Stead stressed, “The future of the world’s coral reefs relies on strong greenhouse gas emissions reduction… and development of approaches to help reefs adapt and recover.”
