Coral reefs are often described as the rainforests of the sea, yet a new global Red List of Coral Reef Ecosystems reveals that these vibrant habitats are sliding into crisis. This assessment, framed through the IUCN Red List of Ecosystems approach, offers an unprecedented, region-by-region view of the overall risk to coral reef ecosystems and the specific drivers behind that risk, from reef loss and heat stress to shifts in coral, algae and fish communities. For anyone concerned about coral reef conservation, it is both a stark warning and a practical guide to where and how action is most urgently needed.

What sets this assessment apart is its dual focus on observed change and projected future risk. Each ecoregion is evaluated not only on its current condition but also on how it is expected to fare under climate change scenarios. That means the Red List of Coral Reef Ecosystems does more than label places as threatened. It helps explain why ecosystems are declining and how their status could worsen as global temperatures rise. This makes it an essential tool for governments, conservation planners and local communities that need to prioritize limited resources.

The regional summaries highlight how different coral regions face distinct combinations of threats and vulnerabilities. In Australia, home to the Great Barrier Reef, 15 of 17 ecoregions are already threatened based on observed change, with four listed as Critically Endangered. Once projected climate change is taken into account, every one of these 17 ecoregions is assessed as Critically Endangered. The picture is similar in other parts of the world, though the specific ecological traits and pressures vary.

Brazil’s coral reefs are relatively species-poor compared with some Indo-Pacific systems, yet many of their coral species are found nowhere else, from the Abrolhos Bank to the isolated reefs of Atol das Rocas and Fernando de Noronha. According to the assessment, five of Brazil’s eight ecoregions are already threatened based on observed change, with three counted as Critically Endangered. Overall, five ecoregions are classified as Critically Endangered and three are considered Data Deficient, highlighting how gaps in monitoring still limit a full picture of risk in some areas.

In the Caribbean, coral loss and depleted fish populations have pushed all ten ecoregions into threatened categories based on current trends. Six are already Critically Endangered. When projected climate change is included, every Caribbean coral reef ecoregion is assessed as Critically Endangered. This region illustrates how multiple local pressures, such as overfishing and pollution, combine with warming seas to drive rapid ecosystem decline.

East Asia, including the Coral Triangle, is renowned as the richest marine region on Earth. Coral cover here is still comparatively high, yet the assessment finds that 22 of 25 ecoregions are already threatened, with five Critically Endangered. Under climate projections, all 25 ecoregions fall into the Critically Endangered category. This contrast between high current biodiversity and very high future risk underscores how fragile even seemingly healthy reefs can be when exposed to sustained warming and intensifying heat stress.

Along the Eastern Tropical Pacific, small and scattered reefs occur along continental coasts and around remote oceanic islands. The study reports that the reefs of the Western Galápagos effectively collapsed after the 1982 to 1983 El Niño event. The remaining nine ecoregions in this region are assessed as Critically Endangered. Here, extreme climate events coupled with underlying vulnerability have translated into ecosystem-scale collapse and pervasive risk.

Across the broader Pacific, which encompasses thousands of islands and atolls from Papua New Guinea to Hawaii and Pitcairn, 19 of 21 ecoregions are already threatened based on observed change, including two Critically Endangered. When future climate warming is factored in, all 21 ecoregions become Critically Endangered. The assessment suggests that even vast, remote archipelagos cannot escape the reach of global climate disruption.

There are a few relative bright spots, though even these come with serious caveats. In the Red Sea and Gulf of Aden, current risk ranges from Vulnerable in the Northern Red Sea and Gulf of Aden to Endangered in southern sections. The heat tolerant corals of the Northern Red Sea are highlighted as a rare example of resilience today, and I found this detail striking because it suggests some reefs may retain a capacity to cope with higher temperatures. Yet when projected climate change is included, all four ecoregions in this region are still classified as Critically Endangered. Resilience has limits in a rapidly warming world.

The ROPME Sea Area, which includes the Arabian (Persian) Gulf, Gulf of Oman and Western Arabian Sea, hosts reefs that already endure some of the hottest and saltiest waters on the planet. All six ecoregions are presently threatened based on observed change, three of them Critically Endangered, and all six are assessed as Critically Endangered overall. In South Asia, covering India, Bangladesh, Sri Lanka, the Maldives and the Chagos Archipelago, every one of the 13 ecoregions is already threatened, largely because they are small and particularly exposed to heat stress. All 13 become Critically Endangered under climate projections.

In the Western Indian Ocean, from Somalia and Kenya down to South Africa and across to Madagascar and nearby island states, 12 of 13 ecoregions are threatened today, and two of those are Critically Endangered. Overall, all 12 assessed ecoregions are classified as Critically Endangered, while the Northern Monsoon Current ecoregion remains Data Deficient. The consistent pattern is hard to ignore. Nearly everywhere, reefs are already under strain, and climate change is projected to push almost all of them into the highest categories of risk.

The authors of the assessment emphasize that this Red List of Coral Reef Ecosystems is more than a diagnostic tool. It offers a shared baseline for countries to track the state of their reefs over time and a methodological foundation for future national Red List of Ecosystems assessments. It is intended to support and inform existing commitments, such as Australia’s Reef 2050 Long-Term Sustainability Plan, the Cartagena Convention and its SPAW Protocol in the Caribbean, the Antigua and Lima Conventions and the CMAR initiative in the Eastern Tropical Pacific, and the Blue Pacific 2050 Strategy.

The message on climate is unequivocal. Cutting greenhouse gas emissions is described as the most important step for coral reef survival, with an emphasis on keeping global warming as close as possible to 1.5 degrees Celsius. The window for effective action is narrowing. At the same time, the assessment stresses that local and national efforts can buy time and build resilience. Strengthening and expanding Marine Protected Areas, restoring key herbivorous fish such as parrotfish and grouper, reducing land-based pollution and controlling invasive species all help reefs better withstand and recover from heat stress.

Another key recommendation is to identify and protect coral reef “bright spots”. These are areas that are thermally tolerant, well connected or otherwise relatively resilient. Safeguarding them is presented as a priority, since they may act as refuges and seed sources for future recovery of threatened ecosystems. Restoration is described as a complementary measure rather than a substitute for tackling root causes. Because restoration is resource intensive and uncertain at large scales, the assessment suggests focusing efforts on ecoregions where coral degradation is high but algae cover is still low and herbivorous fish populations remain well protected, as well as in ecoregions that show noteworthy resilience to warming.

Finally, the Red List of Ecosystems is positioned as a practical policy tool. It is recognized as a headline indicator (A.1) of the Kunming Montreal Global Biodiversity Framework and can support national reporting on goals like restoration (Target 2) and the 30x30 protection target (Target 3). The global coral reef assessment can serve as a starting point for more detailed national assessments, making them faster, more cost effective and more directly relevant for policy makers. The next challenge is to convert the insights from this global diagnosis into concrete, sustained conservation action, and to extend the Red List of Ecosystems approach to other threatened ecosystems around the world.

Funded by the MSC Foundation, with regional contributions from Delta Environmental and Educational Foundation and Global Affairs Canada, this work depended on extensive in kind support from regional partners and the knowledge of more than 250 experts, monitoring programs and local communities. Their shared effort has produced one of the clearest pictures yet of the state of the world’s coral reef ecosystems and what is required to give them a chance to endure.

Read more at https://iucn.org/story/202610/red-list-coral-reef-ecosystems