The reefs of the northern Red Sea are considered among the world's most heat-tolerant coral ecosystems and experienced their first signs of climate-driven bleaching only recently, in 2024. Photo by Dr. Tom Shlesinger, Gulf of Aqaba, Red Sea, 2024.
A University of Portsmouth scientist has helped lead a major global study, which finds that 44% of the world's reef-building coral species are now threatened with extinction - and warns the true figure is likely to be even higher.
Dr Francoise Cabada-Blanco , a marine ecologist in the University's School of the Environment and Life Sciences , is Co-Chair of the International Union for Conservation of Nature (IUCN) Species Survival Commission Coral Specialist Group , which carried out the reassessment.
The group reviewed 892 reef-building coral species on the IUCN Red List of Threatened Species, drawing on data and expertise from more than 60 coral experts around the world. It is the first full update since the first global assessment of reef-building corals in 2008, when around one third of species were found to be threatened.
Of the 774 species with enough data to be classified, 340 (44%) now fall into the highest risk categories: 33 are Critically Endangered, 251 Endangered and 56 Vulnerable.
"Coral reefs are experiencing rapid environmental change, but responses vary greatly among species and regions," said Dr Cabada-Blanco.
"Improving data on regional to local variation in coral and reef responses to threats, in particular climate change, and at species and population level, will improve future reassessments of extinction risk and help managers take action to protect and restore corals around the world."
The full picture is likely worse
The findings use data up to 2020, meaning the assessment was completed before the extraordinary rise in ocean temperatures and the fourth global coral bleaching event of 2023-2025. The authors caution that the proportion of species now at risk is likely to be higher than 44%, with the developing super El Niño of 2026-27 adding further pressure.
Climate change is the main threat to reef-building corals. To build the most complete picture yet, the team combined global trends in coral cover, projections of future severe bleaching events, and the biological traits that make some species more vulnerable than others.
The coral Red List Index - which tracks changes in extinction risk over time, where 1 means no species are at high risk and 0 means all are extinct - has fallen from 0.96 before 1998, to 0.89 in 2008 and 0.74 in 2024. Corals are now showing the fastest increase in extinction risk of any group assessed in this way, ahead of mammals, birds, amphibians, sharks and rays, and cycads.
"This assessment provides the most comprehensive evaluation to date of global extinction risk among reef-building corals, and a stark warning of the accelerating increase in global threats to coral reefs," said Dr David Obura, Dr Cabada-Blanco's fellow Co-Chair of the IUCN Coral Specialist Group and Director of CORDIO East Africa in Kenya.
"It also highlights the challenges we face in addressing major data and knowledge gaps on the status of species at global scales, at the same time as having to take urgent decisions to reduce the drivers of global declines in critical species and ecosystems."
Risk is not spread evenly. Half (50%) of assessed Atlantic species are threatened, compared with 43% in the Indo-Pacific. Among Indo-Pacific Acroporidae - the family that includes the branching staghorn and plating corals that give reefs much of their three-dimensional structure - 191 of 279 species (68%) are classed as Endangered.
Framed by desert mountains, this image highlights the northern Red Sea that harbours one of the world's most distinctive coral reef ecosystems, where local conservation may help preserve reefs with relatively high resistance to climate change. Photo by Dr. Tom Shlesinger, Gulf of Aqaba, Red Sea, 2023.
Every tenth of a degree of avoided warming matters
The study is a snapshot taken while the climate is changing fast. Different coral species, and corals in different places, cope with warming in different ways. That means the future of reefs isn't a simple choice between surviving and disappearing.
It also confirms that corals are heading towards extinction faster than any other group assessed this way, including mammals, birds, amphibians, sharks and rays, and cycads. Their risk is rising at nearly twice the rate of the next fastest group.
Dr Cabada-Blanco added: "Coral reefs can feel a world away from the Solent, but they cover a tiny fraction of the ocean floor, while supporting an enormous share of marine life and the food, coastal protection and livelihoods of millions of people. What happens to them affects all of us. The message from this assessment is that every tenth of a degree of warming we avoid gives corals a better chance - so action now really does count."
Every bit of warming avoided helps. It means more coral species survive, reefs keep working, and corals get more chances to adapt and recover.
The study covers reef-building corals, which live in shallow, warm water and form the colourful reefs found in tropical seas. Separate assessments of cold-water corals, which live in deeper, colder waters, are still under way.
