Australia’s reefs follow trend of global coral cover decline

Australia’s coral reefs are in relatively good condition compared with coral reefs globally, although coral cover on Australian reefs has declined over the past 40 years—reflecting the global trend, a major new report has found.

The Status of the World’s Coral Reefs: 2025 report, released today by the Global Coral Reef Monitoring Network (GCRMN), finds that average hard coral cover measured globally in 2020–24 shows a decline of 9.5% from the reference period of 1980–2009.

The report, the seventh by GCRMN, is the largest and most comprehensive assessment of global coral reef health, covering 10 geographic regions. Four of these regions experienced coral cover declines.

Climate change-driven heat stress has become an increasingly important driver of coral loss in Australia and across the globe over the past decade.

AIMS’ Dr. Manuel Gonzalez Rivero, global coordinator of the GCRMN, said that despite the overall decline, the monitoring data also showed recovery was still possible.

“Globally, there was a 6% relative increase in hard coral cover between 2017 and 2019 after the third Global Coral Bleaching Event, showing reefs still have the capacity to at least partially recover.

“However, this recovery has been reversed by unprecedented loss from the recent fourth Global Coral Bleaching Event.”

The report does not include a full assessment of impacts from the fourth Global Coral Bleaching Event, which includes the 2024 and 2025 mass bleaching events in Australian waters that caused significant coral cover declines across the Great Barrier Reef and Western Australian coral reefs.

Gonzalez Rivero said major disturbances previously occurred on coral reefs once every 10 years. Now, with more frequent Global Coral Bleaching Events, they are occurring every five to six years, reducing the time reefs have to recover.

“Our modeling suggests that if the current rate of Global Bleaching Events is maintained, the long-term decline of global hard coral cover will continue.

“More ambitious reductions in global greenhouse gas emissions offer a more positive future for reefs, when combined with effective management of local pressures,” he said.

Australia follows the global trend—but with differences between reef areas

The report finds that average coral cover on Australian reefs has fallen from 30.2% in the 1980–2009 reference period to 26.8% in 2020–24, a 10.9% relative decline.

One of the lead authors of the Australian chapter of the GCRMN report is Dr. Mike Emslie, who leads AIMS’ Long-Term Monitoring Program on the Great Barrier Reef.

“The assessment shows that Australia’s coral reefs have relatively good coral cover and have largely demonstrated the capacity to recover from disturbances like climate change-driven coral bleaching, cyclones and crown-of-thorns starfish outbreaks if given enough time,” Emslie said.

“But the condition of Australia’s coral reefs varies considerably across the country. Some areas, like Scott Reef off the Northwest Shelf, have been documented to recover after disturbances like the 2016 mass bleaching event. Others, like some reefs in the Southern Great Barrier Reef and the Pilbara region of WA, have experienced recent major declines due to a series of disturbances.

“Despite these differences across Australia, we have still recorded a net loss of coral cover over this long timeframe. What’s not included in this report are further losses from recent mass bleaching events on the Great Barrier Reef and in Western Australia in 2024 and 2025.

“Coral reefs are getting less time to recover between disturbance events and are sometimes being hit by multiple issues in short timeframes.”

GCRMN report co-author and AIMS coral scientist Dr. Emma Kennedy added that it was uncertain whether historic patterns of recovery after disturbance could continue under an increasingly warm climate.

“More frequent and widespread marine heatwaves leading to mass coral bleaching events are shortening the intervals between disturbances and reducing the time available for reefs to recover,” she said.

“Historically, cyclones and crown-of-thorns starfish outbreaks were major causes of decline, particularly on the Great Barrier Reef, but mass bleaching has become increasingly prominent over the past decade.”

AIMS’ monitoring of the Great Barrier Reef has shown a trend of volatility emerging over the past 15 years, with coral cover swinging between very low and very high levels, a shift from the more stable patterns previously observed.

Australia’s coral reefs span at least 43,000 km² (16,600 square miles) of coral reef area—equivalent to about two-thirds of the area of Tasmania—giving it the largest coral reef extent of any nation. Australia is also home to three coral reef World Heritage Areas (the Great Barrier Reef, Ningaloo Coast and Lord Howe Island group), and its reefs are culturally significant for Australia’s First Nations peoples. Around 2 million Australians benefit from healthy reefs through tourism, recreational and commercial fisheries, science and management.

Report co-author and AIMS coral scientist Dr. James Gilmour said Australia is one of the best-monitored reef regions in the world, although monitoring remains uneven.

“Long-term data from areas such as the Great Barrier Reef are excellent, but there are still gaps in our knowledge of Australian reefs, particularly in our northern and northwestern areas, where remoteness, murky waters and safety issues limit monitoring efforts,” he said.

“Expanding the coverage of monitoring will improve our ability to understand Australia’s diverse reef systems and support effective stewardship as climate pressures intensify.

“To help coral reef systems survive climate change, we must reduce emissions, manage coastal development, pollution and fishing pressure, while also developing interventions that help coral reefs adapt to and recover from disturbances.”

International monitoring collaboration is critical for policymakers

The GCRMN is the operational arm of the International Coral Reef Initiative (ICRI). The report, published every five years, is the most detailed evaluation of the long-term trends and condition of coral reefs globally and the threats they face. For 30 years, AIMS has hosted the GCRMN and served as its global coordinator. Gonzalez Rivero said this report was the most comprehensive to date, with three times as much data as the last report.

“This report has analyzed around 21.1 million observations from almost 37,000 reef sites across 120 countries and territories. It is an extraordinary effort from the 600 monitoring partners, who volunteer their contributions.

“This effort is enormous, but so valuable in improving our understanding of coral reefs across the globe and supporting policymakers and managers in how they target their efforts in each region,” he said.

The Australian chapter was written by co-authors from AIMS, the University of New South Wales, WA Museum, the Department of Biodiversity, Conservation and Attractions, James Cook University, The University of Queensland, Australian National University, the University of Tasmania, Reef Check Australia, Reef Life Survey, Citizens of the Great Barrier Reef, Parks Australia, the Great Barrier Reef Marine Park Authority, CSIRO and National Oceanic and Atmospheric Administration (NOAA).

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