Biggest-ever annual coral cover loss across two thirds of Great Barrier Reef

One of the world's seven natural wonders, the reef in late July narrowly escaped being listed globally as "in danger" by UNESCO.

But the official annual survey of coral status shows the northern and southern sections of the reef lost about 25 and 31 per cent of cover respectively after unprecedented global marine heatwaves in 2024 triggered mass coral bleaching.

The government report was released less than two weeks after the World Heritage Committee made its decision to keep the reef off the in-danger list and was not part of the progress report submitted by Australia to the committee in January 2025.

"The summer of 2024 brought multiple stressors to the [reef], including cyclones, flooding and crown-of-thorns starfish, but the mass coral bleaching event was the primary source of coral mortality," the Australian Institute of Marine Science (AIMS) Great Barrier Reef coral condition report for 2024-25 found.

Based on spot surveys taken in the water of 124 individual reefs across a region the size of Italy, the annual update shows nearly half of it lost coral cover and just 10 per cent experienced an increase. The remainder showed little change.

AIMS ecologist Dr Daniela Ceccarelli said the good news was some of the reefs off Townsville in the central region "fared quite well" through the fifth mass coral bleaching event since 2016.

The massive declines further north and south - not seen on this scale in 39 years of monitoring - were partly due to the loss of vulnerable but fast-growing coral species which sprung up like grass and weeds after a bushfire.

"It's all fast-growing coral which is the equivalent of the first things that grow back after a bushfire to cover the soil - and that's great; we need them," Dr Ceccarelli said.

"They are part of the process of recovery, but they're not the full recovery," she said.

"They're fast to grow, but first to go."

While the Great Barrier Reef remained a place of beauty, natural wonder and diversity, it was under threat from increasingly common marine heatwaves, cyclones and extreme weather events.

"We're getting to the point where there's less and less and less time for recovery in between these big heat waves," Dr Ceccarelli said.

"The cyclones are not going to stop. The crown-of-thorns [starfish] are not going to stop. The flooding due to extreme weather events is not going to stop either.

"But the heat waves are what's getting faster, closer together, more extreme, and more widespread."

She said the reef did not have time to recover between bleaching events and good local management could only go so far without also reducing greenhouse gas emissions which cause climate change.

"It can still recover if we give it a chance, but we need to give it a chance," she said.

This is the 39^th consecutive year coral cover has been mapped on the Great Barrier Reef.

The 2024-25 mass bleaching was the reef's sixth such event in less than a decade.

Environment Minister Senator Murray Watt said the AIMS report findings were "very concerning" but "not unexpected" given the marine heatwave.

"It's clear climate change is affecting reefs worldwide, including the Great Barrier Reef," he said.

"It underlines the need for Australia and the world to take urgent action, including reaching net zero emissions."

But he said the federal and Queensland governments were also working on localised protections, including efforts to improve water quality and reduce the impact of crown-of-thorns starfish, as well as limiting high-risk fishing activities.