Miami, Fla. – Florida's iconic staghorn and elkhorn corals have been declared functionally extinct after a record-breaking marine heatwave devastated reefs across the state, according to new research published in Science. Scientists say the 2023 heatwave caused catastrophic losses of these once-abundant reef builders—marking the ninth mass bleaching event in the region.
The Acropora coral species—staghorn (Acropora cervicornis) and elkhorn (Acropora palmata)—were once the backbone of Florida and Caribbean reef systems and have long been the focus of intensive restoration efforts. Their near-total collapse now signals what scientists call a "functional extinction," meaning the species still exist in small numbers but no longer play their vital role in building and sustaining reef ecosystems—a stage that often precedes global extinction.
Led by the National Oceanic and Atmospheric Administration's Coral Reef Watch and Chicago's Shedd Aquarium, researchers at the University of Miami's Rosenstiel School of Marine, Atmospheric, and Earth Science contributed data detailing the coral die-off for the study.
While most other coral species in Florida did not suffer losses as extreme as the more heat-sensitive Acropora, the loss of these species deals a devastating blow to the ecosystem and stands as a stark warning for the future of 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."
The study documents that the temperatures reached during the 2023 heatwave were the highest ever recorded on Florida's Coral Reef in over 150 years, and that the heat stress persisted for 2–3 months. Heat exposure levels were 2.2 to 4 times greater than in any previous year on record.
As the heatwave and mass bleaching event unfolded, the team of researchers conducted diver surveys to track more than 52,000 colonies of staghorn and elkhorn coral across 391 sites. In the Florida Keys and Dry Tortugas (almost 70 miles west of Key West), mortality rates reached a staggering 98–100%. Mortality rates were lower offshore in southeast Florida, at around 38%, reflecting cooler temperatures in the region.
"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 Rich Karp, a co-author and doctoral student at the Rosenstiel School in the Coral Reef Futures Lab when the research was conducted, and later aided in data analysis as a postdoctoral research associate at the Rosenstiel 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."
These two species of coral were already in decline due to decades of disease, poor water quality, previous bleaching events and other human-driven stressors, but the 2023 marine heatwave accelerated the near-total collapse of staghorn and elkhorn corals on the reefs in this region. The population is unlikely to rebound without conservation interventions because of low numbers, continued warming, and additional stressors.
What Happens Next
Scientists have already established living repositories to safeguard remaining Acropora in aquarium facilities on land and in offshore coral nurseries, and have rescued more of the survivors of the 2023 heatwave to bolster these collections. Under expert care, corals in these "gene banks" can continue to grow, supporting further research and restoration efforts for the species. Yet, the authors caution that the success of restoration will ultimately depend on the return time and severity of future bleaching events.
To secure a future for these species, restoration efforts must also scale up new approaches to help corals adapt to changing conditions. Introducing resilient genetic diversity from outside Florida or manipulating the types of symbiotic algae that help corals tolerate heat may be the only means to maintain any Acropora populations in Florida.
"Elkhorn corals, in particular, are some of the most important wave-breaking coral species in the region", said Andrew Baker, professor in the Department of Marine Biology and Ecology, and 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, its worth taking extraordinary measures to ensure we don't lose these corals altogether".
Ultimately, the study underscores that ocean warming from climate change is now surpassing the thermal limits of entire populations of corals. Alongside bold, science-based actions to enhance coral resilience, urgent global action to slow climate change is essential to prevent the collapse of these critical reef ecosystems.
The study titled: Heat-driven functional extinction of Caribbean Acropora corals from Florida's Coral Reef was published on October 23, 2025 in the journal Science. The study involved 47 authors representing 22 institutions. Visit the journal link for complete list of authors.
BACKGROUND ON CORALS: These tiny animals are the building blocks of coral reefs, colorful structures which support 25% of ocean life. In addition to supporting marine life, coral provides food and income for hundreds of millions of people. Corals produce our sandy white beaches and protect our shores from up to 90 percent of potentially damaging waves and flooding. The benefits that coral reefs provide us are estimated to be worth $10 trillion per year globally.
