Coral reef in Papua New Guinea, one of the most diverse marine ecosystems on the planet. — Photo: Tom Shlesinger
Almost half of the coral species responsible for the formation of reefs are threatened with extinction, according to the largest global assessment ever carried out on this group of animals.
The study, published in the journal Nature, analyzed 892 species of reef-building corals. Among the 774 for which there was sufficient data, 340 — or 44% — were classified as threatened.
There are 33 critically endangered species, 251 threatened and 56 vulnerable. The situation has worsened compared to the first global assessment, carried out in 2008, when around a third of corals appeared among the threatened groups.
The main factor behind this deterioration is the warming of the oceans caused by climate change.
Rising temperatures favor bleaching events, when the coral expels the microscopic algae that live in its tissues and provide much of its energy. If the heat persists, the animal may die.
Climate change was decisive for the classification of more than 90% of species that appear in the highest risk groups, according to the researchers.
The work combined data on loss of coral cover, bleaching projections and characteristics that make certain species more vulnerable.
Preserved coral reef in Papua New Guinea, in an area that still shows resistance to the effects of ocean warming. — Photo: Tom Shlesinger
David Obura, one of the study's lead authors and co-chair of the International Union for Conservation of Nature (IUCN) coral specialist group, says the results represent a clear sign that threats are intensifying.
“This assessment provides the most complete overview to date of the global risk of extinction among reef-forming corals,” he says.
The researchers themselves warn, however, that the current situation is probably even worse.
The data used in the assessment goes back to 2020 and therefore does not fully incorporate the three exceptionally warm years between 2023 and 2025 nor the fourth global coral bleaching event.
The study does not calculate what the new percentage of threatened species would be today.
Atlantic and Brazil among most vulnerable areas
Also according to the study, half of the coral species assessed in the Atlantic are threatened with extinction, a proportion above that recorded in the Indo-Pacific, 43%.
In the Southwest Atlantic, especially in Northeast Brazil, the risk is considered particularly high.
The region brings together species with a small distribution and concentrates the highest level of endemism in the Atlantic, that is, it is home to corals that do not exist anywhere else on the planet.
This characteristic means that a local loss can have greater consequences. As there are fewer species performing similar functions, the loss of one of them can have disproportionate effects on the structure of the environment and other organisms that depend on it.
“For an endemic species, a local extinction is a global extinction, because there is no other place for it to persist or from which it can recolonize,” said Francoise Cabada-Blanco, co-chair of the IUCN coral specialist group and professor at the University of Portsmouth, in an interview with g1.
Coral Galaxea fascicularis in the Gulf of Aqaba, Red Sea. The species was classified as least concern in the new assessment. — Photo: Tom Shlesinger
She also highlights that recent impacts reinforce this concern. During the fourth global bleaching event, severe episodes of bleaching and mortality were recorded along an extensive strip of the Brazilian coast.
Among the groups most under pressure are the Acroporidae, branching corals that help form the structure of reefs.
In the Indo-Pacific, 68% of the species assessed in this family were classified as threatened.
In the Atlantic, Acropora cervicornis and Acropora palmata suffered population declines of more than 80%.
The researchers also draw attention to a less visible effect of degradation. A reef can maintain apparently stable cover even after losing more sensitive species, if they are replaced by more resistant ones.
In this process, however, there is a loss of diversity and structural complexity.
