Annual Loss Of Coral Cover Across Great Barrier Reef Worst In 40 Years; 25% Mortality In North, 40% At One Tree Island

The Great Barrier Reef has suffered its biggest annual drop in live coral in two out of three areas monitored by scientists since 1986, a new report has revealed. The Australian Institute of Marine Science (Aims) report is the first to comprehensively document the devastating impacts of the early 2024 mass coral bleaching event – the most widespread and severe on record for the Great Barrier Reef. In the months that followed that event, scientists described a “graveyard of corals” around Lizard Island in the north and a study recorded the death of 40% of corals at One Tree Island in the south.

Aims has conducted annual in-water surveys of the world’s biggest reef system since 1986, checking the health and extent of corals. This year’s survey report found that in the reef’s northern section – between Cooktown and the tip of Cape York – bleaching, two cyclones and associated flooding had caused coral cover to fall by 25%. In the southern section, from Mackay to just north of Bundaberg, coral cover had fallen by 30%. The northern and southern zones suffered the highest annual drops on record.

Coral cover fell by 13% in the central section, which had escaped the worst of the heat in 2024. Dr Mike Emslie, who leads the long-term reef monitoring program at Aims, said coral cover was becoming more volatile. “It has been a pretty sobering year of surveys with the biggest impacts I have seen in the 30-plus years I have been doing this,” he said. “This volatility is very likely a sign of an unstable system. That’s our real concern. We’re starting to see record highs in coral cover that quickly get turned around to record falls.”

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The 2024 and 2025 events were part of an ongoing global mass coral bleaching event that led to more than 80% of the planet’s reefs being hit with enough heat to cause bleaching, affecting corals in at least 82 countries and territories. A study last year found ocean temperatures on the Great Barrier Reef were likely at their hottest for at least 400 years and were an “existential threat” to the Unesco World Heritage-listed reef. Widespread mass bleaching of the Great Barrier Reef was first seen in 1998 and happened again in 2002, 2016, 2017, 2020, 2022, 2024 and 2025.

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https://www.theguardian.com/environment/2025/aug/05/great-barrier-reef-suffers-biggest-annual-drop-in-live-coral-since-1980s-after-devastating-coral-bleaching