The world's coral reefs have lost almost 10% of their hard coral cover over four decades, as the most comprehensive global assessment yet finds damaging events now strike before recovering corals can mature and reproduce.
Given enough time, coral reefs can recover from cyclones, bleaching and other destructive events. But a new report released today suggests they are losing that time.
The Status of Coral Reefs of the World: 2025 is the most comprehensive global assessment of coral reefs yet. Released by the Global Coral Reef Monitoring Network (GCRMN), the report draws on more than 21 million observations from around 90,000 surveys, contributed by 600 partners across more than 120 countries, territories and economies.
The findings show global hard coral cover has declined by 9.5% from an average of 30.2% during the historical reference period of 1980-2009 to 27.3% in 2020-2024.
Four global coral bleaching events, caused by climate-driven marine heatwaves, were the main cause of the loss.
"We have entered a time when disturbance is a regular feature of coral reefs," says UNSW Sydney's Associate Professor Tracy Ainsworth, a report coauthor and current vice-president of the International Coral Reef Society .
Major bleaching events previously occurred about once a decade. Since 2010, they have occurred approximately every five to six years. But many corals need at least five years just to mature and begin reproducing.
"In some places, severe disturbance is already happening annually. In others, it is happening every few years," A/Prof. Ainsworth says.
"The growth and maturity timeline that corals need is now being overwhelmed by stress and disturbance events."
This means established corals can disappear faster than a new generation can grow and repopulate the reef.
"The large corals we expect to see on reefs can be decades old," A/Prof. Ainsworth says.
"When they are lost, it takes decades for that population structure to return.
"But that timeline is now interrupted by more, and increasingly severe, stress events, making it harder for new corals to grow and fill the reef."
Recovery, but not as we know it
The report provides some evidence of reefs' resilience. Global hard coral cover increased by 6% from 2017 to 2019 following the third global bleaching event.
But those gains were reversed by the unprecedented coral loss associated with the fourth global bleaching event, which began in 2023 and continued into 2025. The event resulted in substantial losses from the 2024 mass bleaching event on the Great Barrier Reef and severe bleaching of Western Australian reefs in 2025.
The fourth global bleaching event produced the largest decline in hard coral cover in the 45-year record, although its full effects are not captured in the report.
A/Prof. Ainsworth says the capacity for recovery depends on retaining healthy, diverse reef areas that can continue supplying new corals to damaged sites. But that requires some reefs to escape bleaching, storms and land-based pollution, or, at least, for some corals to survive and reproduce afterwards.
"Unfortunately, we are now seeing more frequent bleaching events, more severe storms and more land-based pollution," she says.
"Recovery to the reefs we enjoyed before 2016 is increasingly unlikely under these conditions."
Rather than expecting damaged reefs to return to their previous state, scientists are increasingly considering how coral ecosystems might reorganise in response to warmer oceans and more severe disturbances.
"We are now talking about the restructuring of coral reef ecosystems into systems that can withstand a new climate of higher temperatures and more severe storms," A/Prof. Ainsworth says.
While coral cover could return, the original reef ecosystem will not, she says. The mix of coral species, physical structure and ecological relationships are becoming entirely different.
Global figure masks local losses
The global 9.5% decline also conceals substantial differences between reefs and regions.
Some locations have experienced far greater losses because they face repeated marine heatwaves combined with local pressures such as poor water quality. Other reefs have so far been less exposed to extreme warming.
"Inshore coral reefs, for example, are affected by both severe stress events and land-based pollution," A/Prof. Ainsworth says.
While Australia's reefs remain in comparatively good condition, they have followed the broader global decline.
Average Australian hard coral cover fell from 30.2% during the 1980-2009 reference period to 26.8% between 2020 and 2024, representing a relative decline of 10.9%.
"Compared with places that have experienced much greater decline, 10% is not as bad," A/Prof. Ainsworth says.
"But that's not what we should be aiming for."
Recovery to the reefs we enjoyed before 2016 is increasingly unlikely under these conditions.
From coral reefs to algal reefs
When corals die, the fish and other marine species that depend on coral for food and shelter can also begin to disappear. And when that happens, the empty space does not remain empty for long.
Another warning sign in the report is a 44% increase in average global macroalgae cover compared with the historical reference period.
Macroalgae occurs naturally on reefs, but a major increase can restrict coral recovery by taking over where young corals need to establish.
"Algae takes over the free spaces corals have to recruit and repopulate the reef," A/Prof. Ainsworth says. "More algae means less space, which means less coral.
"The ecosystem fundamentally changes away from a coral reef and into an algal reef and a very different ecosystem. And so the species that rely on corals for habitat and food are then also lost from the reef."
Researchers are searching for 'bright spots' - reefs or coral communities that may be adapting more successfully to repeated heat stress. But A/Prof. Ainsworth says it is too early to know whether some reefs are genuinely adapting better than others.
"We are only just over 10 years into an era of severe and recurrent disturbance events," she says.
"Corals are long-lived organisms. We are only now seeing the beginning of those impacts, while more disturbances continue to arrive on the reefs."
Exceptional stake, exceptional responsibility
"Australia has responsibility for 17% of the world's reefs," A/Prof. Ainsworth says. "Every reef that can be protected should be protected."
The nation is home to at least 43,000 square kilometres of coral reef, equivalent to around two-thirds the area of Tasmania, which represents the largest extent attributed to any single country.
"We should be doing everything we can to ensure that these ecosystems have the best possible chance of restructuring into systems that continue to be of high natural value."
The report's modelling suggests coral cover will continue its downward trajectory if global bleaching events persist at their current frequency.
More ambitious reductions in greenhouse gas emissions offer a better outlook, particularly when combined with effective management of local pressures.
"Without question, we must slow the trajectory of ocean warming," A/Prof. Ainsworth says.
"We cannot expect that thousands of species will simply adapt within the timeline of warming we have created - and deliver us ecosystems that we can continue to enjoy and value."
What can we do?
While emissions reduction is essential, A/Prof. Ainsworth says governments and communities can immediately improve reefs' chances by reducing pollution and maintaining high water-quality standards.
"Water quality will play a crucial role in how coral reefs restructure under the coming changes," she says.
"By ensuring the highest standards for water quality, we remove additional stressors that could otherwise amplify the impacts of a changing climate - providing a clean environment that can support a diverse ecosystem."
A/Prof. Ainsworth says the future of coral reefs might look different to the past - but we can have an impact on what that future looks like.
"While corals possess the biological capacity to recover, like any living organism they need the time and healthy conditions to do so."
The Global Coral Reef Monitoring Network (GCRMN) is an operational network of the International Coral Reef Initiative (ICRI), supporting its efforts by working through a global collective to strengthen the provision of best available scientific information on, and communication of, the status and trends of coral reef ecosystems, for their conservation and management.
