The Great Barrier Reef has suffered its steepest coral loss in almost four decades, with some regions seeing a dramatic drop of over 70% in hard coral cover, according to a new government survey. Scientists are sounding the alarm, warning that time is running out to protect one of the world’s most vital marine ecosystems.
A report released on August 6 by the Australian Institute of Marine Science (AIMS) confirms that the 2024 mass coral bleaching event—driven by extreme marine heat—had the largest footprint ever recorded in the 39 years of long-term reef monitoring. The bleaching coincided with record-high sea temperatures, damaging cyclones, and outbreaks of crown-of-thorns starfish, which prey on coral.
Sharp Declines Across the Reef
The AIMS survey, conducted between August 2024 and May 2025, covered 124 reefs across the northern, central, and southern parts of the reef. Nearly half (48%) of the surveyed reefs showed a decline in coral cover, while only 10% experienced any recovery.
The northern section experienced the most dramatic loss, with average hard coral cover falling by 24.8%, from 39.8% to 30%. This decline was especially severe around Lizard Island, where record heat stress combined with cyclones and freshwater flooding caused widespread damage.
In the central region, coral cover dropped by nearly 14%, while the southern reef witnessed the sharpest relative decline—losing over 30% of its coral cover in just one year. Many southern reefs, especially in the Capricorn-Bunker group, suffered their steepest coral losses since records began.
A Pattern of Repeated Bleaching
The 2024 bleaching was the fifth such event since 2016 and part of a broader global coral bleaching emergency that began in 2023. According to AIMS scientists, these mass events are becoming more frequent and more intense, leaving the reef little time to recover.
AIMS Long-Term Monitoring Program lead Mike Emslie noted that the reef is now showing signs of greater instability, with hard coral cover swinging between record highs and devastating lows in short periods. This, he said, reflects an ecosystem increasingly under stress.
Particularly concerning is the loss of Acropora corals—fast-growing, reef-building species that are especially vulnerable to heat, storms, and starfish predation. These corals had previously driven much of the reef’s recovery from earlier bleaching episodes.
An Urgent Call for Action
Selina Stead, AIMS Chief Executive, said the reef is now facing back-to-back bleaching events more frequently. “This is the second time in just ten years that the Great Barrier Reef has experienced mass bleaching in two consecutive years,” she said.
Globally, coral reefs are under similar threat. Between January 2023 and May 2025, nearly 84% of the world’s coral reef areas had been exposed to bleaching-level heat stress, with documented bleaching in at least 83 countries and territories, according to the U.S. National Oceanic and Atmospheric Administration (NOAA).
With the full impact of the 2025 event yet to be assessed, scientists are urging rapid climate action and stronger marine protections to preserve what’s left of the reef.
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