気候変動：造礁サンゴ種のほぼ半数で相対的な絶滅リスクが高い

Around 44% of reef-building coral species are estimated to face an increased relative risk of extinction, according to an assessment of 774 reef-building coral species on the International Union for Conservation of Nature (IUCN) Red List, published in Nature this week. The analysis suggests that projected heat stress associated with climate change is the primary driver of population declines. These findings reinforce the importance of limiting further warming to protect coral biodiversity and maintain reef ecosystem function.

Coral reefs support a wide variety of marine life and provide economic and social benefits to more than 100 tropical countries. Warming associated with climate change is a major threat to coral reefs, causing bleaching events with increasing frequency. In 2008, one-third of reef-building corals were classified as threatened in the first assessment of IUCN Red List status coral, based on coral cover data aggregated across species, and declines have been escalating in recent years as temperatures continue to increase.

David Obura, Beth Polidoro, Francoise Cabada-Blanco and colleagues sought to update these figures by reassessing the IUCN Red List status of reef-building coral species. Population reductions were inferred from coral cover trends aggregated across species and projections of annual severe bleaching under a ‘middle of the road’ climate change scenario called SSP2-4.5. The IUCN Red List of Threatened Species is a measure used to determine the relative risk of extinction for different species. Of the 774 coral species assessed, 340 (44%) had a higher relative risk of extinction. The values varied by region; in the Indo-Pacific, which includes the Great Barrier Reef, 43% of coral species were threatened, whereas 50% of species were classified as threatened in the Atlantic. The ‘high risk’ level is divided into 3 levels. At greatest risk, 33 species are classed as Critically Endangered, 251 as Endangered, and 56 as Vulnerable. For 93% of the species considered to be at high risk, heat stress in the coming 30 years was the most important driver.

The authors note that the proportion of threatened species may be even higher now as these findings predate the three hottest years on record between 2023 and 2025, which included a global coral bleaching event. Based on evidence of the last 3 decades, they warn that greater efforts are needed to limit warming to protect the remaining coral populations. The authors explain that the assessments in this study are based on total coral cover data aggregated across species, which serves as a proxy for estimating declines rather than providing direct observations. This limitation could be addressed in the future as more observational data become available.
 

• Article
• Published: 15 October 2026

Obura, D.O., Polidoro, B., Cabada-Blanco, F. et al. Nearly half of reef-building corals face elevated relative risk of extinction. Nature (2026). https://doi.org/10.1038/s41586-026-11263-3