Florida's once-thriving staghorn and elkhorn corals have been declared functionally extinct following a record-breaking marine heatwave that devastated reefs in the state's coastal waters. Scientists say the 2023 heatwave caused catastrophic losses among these key reef-building species - marking the ninth mass bleaching event in the region's history. The Acropora coral species - staghorn (Acropora cervicornis) and elkhorn (Acropora palmata) - were once the backbone of reef ecosystems in Florida and the Caribbean and have long been the focus of major restoration efforts. Their near-total collapse now represents what scientists call a "functional extinction", meaning the species survives in small numbers but no longer fulfil their vital ecological role in sustaining reef habitats-a stage that often precedes total extinction. The study was led by the National Oceanic and Atmospheric Administration's (NOAA) Coral Reef Watch and Chicago's Shedd Aquarium, with researchers from the University of Miami's Rosenstiel School of Marine, Atmospheric, and Earth Science contributing data documenting the coral die-off. While many other coral species in Florida escaped such extreme damage, the loss of these two heat-sensitive Acropora species is described as a devastating ecological blow-and a stark warning for coral reefs worldwide. "We're running out of time," said the study's co-first author, Ross Cunning, a research biologist at Shedd Aquarium and adjunct assistant professor at the Rosenstiel School. "Extreme heatwaves are increasing in frequency and severity due to climate change, and without immediate, ambitious actions to slow ocean warming and boost coral resilience, we risk the extinction of even more corals from reefs in Florida and around the world." Researchers reported that temperatures during the 2023 heatwave were the highest recorded on Florida's Coral Reef in more than 150 years, with extreme heat stress persisting for up to three months. Heat exposure levels were found to be between 2.2 and four times higher than in any previous year on record. During the event, divers surveyed more than 52,000 colonies of staghorn and elkhorn coral across 391 sites. In the Florida Keys and Dry Tortugas, mortality rates reached an astonishing 98-100%. Offshore reefs in southeast Florida fared slightly better, with losses of around 38%, thanks to cooler local conditions. "This study quantifies the severe losses of acroporid corals during the 2023 marine heatwave along Florida's Coral Reef, which has significant implications for its future trajectory and management," said co-author Rich Karp, a doctoral student at the Rosenstiel School's Coral Reef Futures Lab during the research, later working as a postdoctoral associate at the school's NOAA Cooperative Institute for Marine and Atmospheric Studies. "Therefore, preserving as much genetic diversity as possible, identifying survivors on the reef, and introducing additional genetic diversity are necessary to protect this essential reef-building species." In a bid to save the coral, scientists have begun safeguarding surviving Acropora in aquarium facilities and offshore nurseries, creating "living gene banks" where corals can grow under controlled conditions. These repositories will serve as sources for research and future restoration efforts. However, experts caution that the long-term success of restoration will depend heavily on the frequency and intensity of future heatwaves. To ensure any future for these corals, restoration programmes are now exploring more radical approaches-such as introducing resilient genetic strains from outside Florida or altering the symbiotic algae that help corals withstand heat. "Elkhorn corals, in particular, are some of the most important wave-breaking coral species in the region," said Professor Andrew Baker, director of the Coral Reef Futures Lab at the Rosenstiel School. "They used to be common on shallow reef crests in the Caribbean, and if we want our reefs to continue protecting our coastlines from flooding during storms, it's worth taking extraordinary measures to ensure we don't lose these corals altogether." The study warns that ocean warming driven by climate change is now exceeding the thermal limits of entire coral populations. Alongside urgent efforts to boost coral resilience, scientists say bold global action to curb greenhouse gas emissions will be essential to prevent the collapse of reef ecosystems worldwide. The paper, titled Heat-driven functional extinction of Caribbean Acropora corals from Florida's Coral Reef, was published on 23 October 2025 in Science. It involved 47 authors from 22 institutions.