Coral Reefs: The GCRMN’s latest report raises the alarm, but the future is still to be written
Authors: Jérémy Wicquart, Francis Staub, Victor Brun
Heatwaves also happen underwater
The heatwaves that hit Europe during the summer of 2026 will likely be remembered for their intensity and duration. Their consequences are clearly visible, from numerous dried-up rivers to vast forest fires, as well as mass wildlife die-offs. But some of these upheavals remain hidden from our view. Beneath the ocean’s surface, marine ecosystems are also experiencing heatwaves. Among the most vulnerable are coral reefs.Hard corals, which grow by forming a limestone skeleton, are the main builders of coral reefs, to which they have given their name. These colonial animals, related to jellyfish but attached to the ocean floor, live in symbiosis with microalgae that they host within their tissues. These microalgae provide corals with most of their energy through photosynthesis. But during a marine heatwave, this symbiotic relationship breaks down. The corals then expel their microalgae, revealing their white skeleton through the translucent tissue - a phenomenon known as “coral bleaching.” If the marine heatwave persists, the corals may eventually die.
A new global report
Observing these changes on a planetary scale requires looking far beyond any single reef. This is precisely the objective of the Global Coral Reef Monitoring Network (GCRMN), which has just published the seventh edition of its assessment of the state of the world’s coral reefs. Based on the aggregation of data from more than 87,000 surveys conducted in these ecosystems over the past forty years, and drawing on the expertise of more than 200 scientists and experts, this new report provides a clear picture of recent changes in coral reefs worldwide.
The decline of coral reefs
The report’s findings show that coral cover was, on average, 9.5% lower during the recent period (2020–2024) than during the historical reference period (1980–2009). In other words, the proportion of the seafloor covered by living corals has declined by nearly 10% in just 40 years. Sharp declines in coral cover occurred following the global bleaching events of 1998, 2010, 2016, and 2024.
Recovery - provided there is enough time
Coral reefs are capable of recovering between global bleaching events, as demonstrated by the increase in coral cover between 2017 and 2019. But resilience requires time. Following significant mortality, the growth of surviving corals and the establishment of new ones take several years. When marine heatwaves—the cause of bleaching events—become too frequent, coral reefs do not have enough time to recover before being impacted again. Climate change, however, is increasing the frequency, intensity, and duration of marine heatwaves, progressively reducing the time available for reefs to rebuild between disturbances.
Different regional trajectories
The global trend masks highly contrasting regional trajectories. Of the ten regions studied, four showed a decline, two an increase, and four no detectable change. These differences show that, despite an increasingly unfavorable global climate, not all reefs respond in the same way. Their trajectories depend particularly on their past exposure to disturbances, their ecological and environmental characteristics, as well as the human pressures that are locally added to the effects of climate change.
Act locally, act globally
Between 2000 and 2020, the human population living near coral reefs increased by 46%. This growth has inevitably been accompanied by coastal development, resulting in deteriorating water quality and increased pressure on marine resources. However, local actions can significantly limit the impacts of human societies on coral reefs.The implementation of effective sanitation systems can reduce the amount of nutrients—primarily nitrogen and phosphorus—entering coastal waters and help curb the proliferation of algae that compete with corals. These same algae can be consumed by herbivorous fish, whose populations benefit from certain management measures, such as marine protected areas.Some actions must also be considered more broadly, recognizing the continuity between terrestrial and marine ecosystems. Tackling deforestation, for example, helps limit coastal erosion and therefore the amount of sediment entering coastal waters, where it can smother corals. In addition, a transition toward more sustainable agricultural practices can reduce the use of pesticides and their runoff into the sea, where they poison corals and reef organisms.International commitments to protect 30% of the ocean by 2030 will remain insufficient for coral reefs if the waters surrounding these protected areas continue to warm. An urgent and massive reduction in greenhouse gas emissions is therefore essential to limit climate change. This will require action at every level of society, from individuals to governments, as well as businesses and local authorities.The available levers for action are numerous and include, in particular, the development of renewable energy, the electrification of energy uses, and an end to new fossil fuel extraction projects.
Monitoring to improve protection
Alongside these conservation efforts, it is essential to continue funding programs that monitor the condition of coral reefs. The data collected by divers as part of these programs make it possible to assess the effectiveness of conservation measures and improve them over time. Too often overlooked, monitoring programs are nevertheless one of the essential conditions for the success of conservation efforts and must therefore receive long-term funding.
The future of coral reefs has not yet been written
Since the first edition of the Status of Coral Reefs of the World, published in 1998, the GCRMN has documented changes in coral reefs worldwide. Its new report delivers a message that is both concerning and hopeful: coral reefs can recover, but only if we give them enough time.The future of these ecosystems has not yet been written, and the scientific evidence is clear on this point. It will depend largely on our ability to limit climate change while reducing local pressures. The trajectory presented in the GCRMN’s next global assessment will therefore depend as much on the reefs’ capacity for resilience as on the political decisions we make today regarding climate, biodiversity, and our coastlines.
Protecting Reefs: A Matter of Climate Justice
For many Europeans living on the continent, coral reefs primarily evoke distant landscapes teeming with life and color. But for several hundred million people living in tropical regions, these ecosystems directly contribute to food security, livelihoods, and protection of coastlines from waves and cyclones.Their disappearance would therefore primarily affect populations whose historical contribution to climate change has been relatively small. Protecting coral reefs is thus not only a matter of preserving biodiversity; it is also a matter of climate justice.