New Study Documents Functional Extinction of Two Critically Endangered Coral Species Following Record Heatwave in Florida

Key Largo, FL – Data from NOAA’s Mission: Iconic Reefs (M:IR) provided critical context for a new research paper published in Science that reports the functional extinction of Acropora corals from Florida’s Coral Reef. M:IR field team members were among those who documented catastrophic mortality of these critically endangered corals following a record-setting marine heatwave in 2023 that marked the ninth mass bleaching event for the region. Both Acropora coral species—staghorn (Acropora cervicornis) and elkhorn (Acropora palmata)—are important reef-builders in Florida and the Caribbean and have been a major focus of recent coral restoration efforts. 

 “Documenting the effects of the 2023 heatwave was devastating from a personal perspective, and something the Florida Keys science community will never forget,” said M:IR Research and Monitoring Coordinator Dr. Katey Lesneski. “Professionally, it provided a remarkable opportunity to gather data that will help us advance the science of coral restoration.”

Led by the National Oceanic and Atmospheric Administration’s Coral Reef Watch and Chicago’s Shedd Aquarium, the study involved 47 authors representing 22 institutions, including M:IR’s Lesneski, Dr. Andy Bruckner, and Grace Hanson, who contributed data detailing the coral die-off and assisted in reviewing and editing the publication. While some individual elkhorn and staghorn corals remain, their numbers are now so low that they can no longer fulfill their vital roles in the ecosystem—providing habitat for marine life and helping protect coastlines. This collapse of ecological function marks what scientists call a functional extinction—a stage that often precedes global extinction or the complete disappearance of species. 

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.

“Moving forward, it will be critical to continue to preserve these corals in gene banks, whether on land or in carefully curated nurseries, so that we don’t lose genetic lineages entirely,” Lesneski said. “On the restoration front, aggressive interventions are necessary at this point – whether that involves creating more thermally tolerant lineages through crossbreeding with individuals from other Caribbean regions, or beneficial manipulations of the coral-algae symbiotic relationship. Indeed, restoration success for these species may be limited to localized areas and will depend on the severity of future bleaching events.” 

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.

Science is the peer-reviewed academic journal of the American Association for the Advancement of Science and one of the world’s top academic journals. It was first published in the 1880s, and readership today exceeds 400,000. “Our data collection wrapped up a year and a half ago, but articulating the story through the scientific journal process is rigorous, and publication of the study in Science validates the quality of the work we are doing at Mission: Iconic Reefs,” said Lesneski.