Nearly half. A reassessment of 892 reef-building coral species for the IUCN Red List, published in Nature on October 15, 2026, found that 340 of the 774 species with enough data to assess (44%) qualify as threatened. Of those, 33 species were classed as Critically Endangered, 251 as Endangered and 56 as Vulnerable, mostly because of projected population declines from ocean warming and severe bleaching.
The species were first assessed in 2008, and the authors note that the new findings predate the three hottest years on record and the fourth global coral bleaching event (2023–2025), so the true situation may be worse. The Red List ranks relative extinction risk; it does not predict whether or when a species will go extinct.
Image: Coral reef at Palmyra Atoll National Wildlife Refuge, Jim Maragos/U.S. Fish and Wildlife Service, CC BY 2.0, via Wikimedia Commons.