Parts of the Great Barrier Reef have experienced their largest annual coral decline on record.
The Australian Institute of Marine Science (AIMS) has led annual surveys of the reef for the last 40 years.
AIMS collected data for its latest report between August 2024 and May 2025. It found consecutive mass bleaching events caused excessive damage to the reef.
The summer period also brought “multiple stressors” to the reef, including cyclones, flooding and increased numbers of crown-of-thorns — a coral-eating starfish.
GBR
The Great Barrier Reef (GBR) is the world’s largest coral reef system.
It's 3000 individual reefs cover a 344,400 square kilometre area (approximately the size of Germany) off the coast of Queensland.
The reef is home to thousands of species of marine life and coral.
The GBR was added to the UNSECO World Heritage List in 1981, and is one of the seven natural wonders of the world.
Areas of GBR
The GBR can be broken into three areas: The north, central, and south regions.
Historically, the north and central regions (which are closer to the equator) have seen the most dramatic environmental decline as a result of warming waters.
The south has been relatively more stable and reliable for environmental growth.
AIMS
The Australian Institute of Marine Science (AIMS) is a tropical marine research agency. The Government body is considered a world leader in marine science.
AIMS has been monitoring the long-term health of the GBR since 1983. It conducts annual surveys to measure “the status and trend of hard coral cover on reefs” across all three GBR regions.
In its latest report, AIMS said it observed “high to extreme” coral bleaching prevalence across all three regions of the GBR in 2024.
Findings
Between May 2024 and May 2025, AIMS found the sharpest decline in coral cover since it began collecting data four decades ago.
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Specifically, coral declined by:
- 25% in the northern region
- 14% in the central reef
- 31% in the reef’s south
AIMS said the decline follows a period of “above-average water temperatures,” which peaked in March 2025.
“As a result, the GBR experienced its sixth mass coral bleaching event since 2016,” the report noted.
Researchers noted “mass coral bleaching events are now occurring with increasing frequency, while recovery periods are decreasing”.
However, AIMS stated the GBR had “record high coral cover” before the bleaching event, and has retained “higher coral cover than many reefs globally”.
Previous recovery of the reef was largely driven by the resilience of fast-growing coral species, but some species haven’t been able to withstand the latest marine heatwave.
Below are the latest images from the GBR showing the impacts of bleaching.
Before bleached corals become white, they produce special proteins in response to heat stress that make them turn very bright pastel and fluorescent colours.
Bleached hard coral colonies at Miall Island on the Southern GBR
Response
The Australian Marine Conservation Society said climate change “is outpacing the Reef’s ability to recover.”
Responding to the AIMS report, it noted: “For the first time, substantial bleaching impacts were recorded in the southern Reef, showing that almost the entire system has been hit hard, not just isolated areas.”
Climate Change Minister Chris Bowen called the findings “deeply concerning but entirely unsurprising”.
“It’s in our national interest to keep going to net zero to protect [the GBR,] he said.
