The world's coral reefs are confronting a mounting crisis as marine heatwaves strike with increasing frequency, leaving reefs little time to recover between bleaching events, according to a major new report from the Global Coral Reef Monitoring Network (GCRMN).
The report, released on Monday, 31 August, draws on more than 21 million observations from 36,886 reef sites across 124 countries and territories, gathered over more than 40 years. It finds that the proportion of reef surface covered by living coral — known as hard coral — has fallen by 5 percent compared with the 1980–2009 average, and that global coral cover is now well below normal levels and at risk of irreversible decline.
Lead author Manuel Gonzalez Rivero, a scientist at the Australian Institute of Marine Science, said that while corals have the capacity to recover given sufficient time, that time is no longer being granted. "If we give them enough time, they have the capacity to recover," he said. "But we haven't seen that amount of time being allowed. In fact, the frequency of those bleaching events has pretty much doubled."
The Mechanism of Bleaching and Decline
Bleaching occurs when abnormally warm sea temperatures cause corals to expel the colourful algae living in their tissues. Without these algae, corals become vulnerable to starvation and disease. While bleached corals are not dead, they require cooler waters to recover, and if heat persists long enough, they die.
The report's researchers attribute the decline primarily to climate-driven heat stress, a process that has now occurred four times since 1998 at ever-shorter intervals. Gonzalez Rivero noted that coral cover remained relatively stable for decades before a sharp downturn: "We had 40 years of coral cover around the world that had remained relatively unchanged until 2010. Since 2010, there has been a very steep change."
Data from the report indicate that hard coral cover fell from just over 30 percent during the 2009–2020 period to 8 percent in 2024. The latest major bleaching event, in 2023, was the most extensive on record, affecting 77 percent of the world's coral reef areas. Gonzalez Rivero warned that another such event is "very likely" this year given elevated global temperatures.
Reefs' Ecological Significance
Coral reefs, despite covering less than 1 percent of the ocean floor, support more than a quarter of all marine life. As such, they serve as critical indicators of ocean health, and their decline carries profound implications for marine biodiversity and the communities that depend on reef ecosystems.
The GCRMN's warning comes as the Pacific Islands Forum, an 18-nation group long viewed as a symbol of regional unity, prepares for its upcoming summit. Organisers have announced that at least five leaders will skip the meeting, which is used to discuss pressing issues facing Pacific states, including climate change and ocean health.