A recent report indicates that portions of the Great Barrier Reef have experienced the most substantial annual decline in coral cover since record-keeping began nearly four decades ago.
The Australian Institute of Marine Science (AIMS) revealed that both the northern and southern regions of the vast Australian reef have suffered the most extensive coral bleaching on record.
While tropical cyclones and outbreaks of crown-of-thorns starfish, which prey on coral, have impacted reefs in recent months, AIMS identifies heat stress resulting from climate change as the primary driver of the decline.
AIMS cautions that the reef habitat may be approaching a critical threshold where coral cannot recover sufficiently between catastrophic events, leading to a “volatile” future.
The health of 124 coral reefs was assessed by AIMS between August 2024 and May 2025, continuing a surveying program initiated in 1986.
Often referred to as the world’s largest living structure, the Great Barrier Reef is a 2,300km (1,429-mile) expanse of tropical corals that supports a remarkable array of biodiversity. Recurring bleaching events are causing once-vibrant coral to turn white across vast areas.
Coral is essential to the health of the planet. Known as the “sea’s architect,” coral builds extensive structures that provide habitat for an estimated 25% of all marine species.
Coral bleaching occurs when coral experiences stress and turns white due to excessively warm water temperatures.
Stressed coral is likely to die if exposed to temperatures 1C (1.8F) above its thermal limit for two months. If water temperatures are 2C higher, survival is limited to approximately one month.
Unusually warm tropical waters triggered widespread coral bleaching on the Great Barrier Reef in 2024 and in the early months of 2025, marking the sixth such event since 2016.
In addition to climate change, natural weather patterns like El Niño can also contribute to mass bleaching events.
The report indicates that the reef has “experienced unprecedented levels of heat stress, which caused the most spatially extensive and severe bleaching recorded to date.”
The report also notes that any recovery could take years and is contingent upon future coral reproduction and minimal environmental disturbance.
The latest AIMS survey results reveal that Acropora species were the most affected corals, as they are particularly vulnerable to heat stress and are a preferred food source for crown-of-thorns starfish.
“These corals are the fastest to grow and are the first to go,” AIMS research lead Dr. Mike Emslie told ABC News.
“The Great Barrier Reef is such a beautiful, iconic place, it’s really, really worth fighting for. And if we can give it a chance, it’s shown an inherent ability to recover,” he stated.
The Australian government’s crown-of-thorns starfish culling program has achieved some success, eliminating over 50,000 starfish through injections of vinegar or ox bile.
“Due to crown-of-thorns starfish control activities, there were no potential, established, or severe outbreaks of crown-of-thorns starfish recorded on Central GBR reefs in 2025,” the AIMS report stated.
While native to the Great Barrier Reef, these creatures are capable of consuming vast quantities of coral. Their numbers have increased significantly since the 1960s, with nutrient runoff from land-based agriculture considered the most probable cause.
Richard Leck, from the global environmental charity WWF, stated that the report demonstrates that the reef is an “ecosystem under incredible stress.” He told news agency AFP that scientists are concerned about the consequences if “the reef does not keep bouncing back the way it has.”
Leck cautioned that some coral reefs worldwide are already beyond recovery and warned that the Great Barrier Reef could suffer the same fate without ambitious and rapid climate action.
The Great Barrier Reef has held heritage listing status for over 40 years, but Unesco has warned that the Australian icon is “in danger” due to warming seas and pollution.
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