2 Iconic Coral Species Are Now Functionally Extinct Off Florida, Study Finds – We Witnessed the Reef’s Bleaching and Devastation
- camilarosiaz
- Jan 28
- 3 min read
In early June 2023, the coral reefs in the lower Florida Keys and the Dry Tortugas were stunning. We were in diving gear, checking up on hundreds of corals we had transplanted as part of our experiments. The corals’ classic orange-brown colors showed they were thriving.
Healthy staghorn coral were crucial builders of Florida’s coral reef. Today, few survive there. Maya Gomez
Just three weeks later, we got a call – a marine heat wave was building, and water temperatures on the reef were dangerously high. Our transplanted corals were bleaching under the heat stress, turning bone white. Some were already dead.
That was the start of a global mass bleaching event. As ocean temperatures rose, rescuers scrambled to relocate surviving corals to land-based tanks, but the heat wave, extending over 2023 and 2024, was lethal.
A bleached and dead staghorn coral thicket in the Dry Tortugas, already being overgrown by seaweed in September 2023. The corals had been healthy a few months earlier. Maya Gomez
In a study published Oct. 23, 2025, in the journal Science, we and colleagues from NOAA, the Shedd Aquarium and other institutions found that two of Florida’s most important and iconic reef-building coral species had become functionally extinct across Florida’s coral reef, meaning too few of them remain to serve their previous ecological role.
In summer 2023, the average sea-surface temperature across Florida’s reef was above 87 degrees Fahrenheit (31 degrees Celsius) for weeks. We found that the accumulated heat stress on the corals was 2.2 to 4 times higher than it had ever been since modern satellite sea-surface temperature recordings began in the 1980s, a time when those two species – branching staghorn and elkhorn corals – were the dominant reef-builders in the region.
Live elkhorn coral, Acropora palmata, off Florida before the marine heat wave. NOAA Fisheries
Everywhere on the reef, corals were bleaching. That occurs when temperatures rise high enough that the coral expels its symbiotic algae, turning stark white. The corals rely on these algae for food, a solar-powered energy supply that allows them to build their massive calcium carbonate skeletons, which we know as coral reefs.
By the end of summer 2023, only three of the 200 corals we had transplanted in the Lower Keys to study how corals grow survived. In the Dry Tortugas, corals’ bone-white skeletons were already being grown over by seaweed. That’s a warning sign of a potential phase shift, where reefs change from coral-dominated to macroalgae-dominated systems.
Of the more than 50,000 acroporid corals surveyed across nearly 400 individual reefs before and after the heat wave, 97.8% to 100% ultimately died. This pattern of bleaching extended to the rest of the Caribbean and the world, leading NOAA to declare 2023-2024 the fourth global bleaching event.
A bleached colony of elkhorn coral in Dry Tortugas National Park off Florida on Sept. 11, 2023. Shedd Aquarium/Ross Cunning
Even before the 2023 marine heat wave, staghorn and elkhorn numbers had been dwindling, with punctuated declines accelerated by a diverse array of stressors – hurricane damage, loss of supporting herbivore species, disease and repeated bleaching. The 2023-2024 event was effectively the final nail in the coffin: The data from our new study shows that these species are now functionally extinct on Florida’s coral reef.
Caribbean acroporids have not entirely disappeared in Florida, but those left are not enough to fulfill their ecological role. When populations become too small, they lose their capacity to rebound – in conservation biology this is known as the “extinction vortex.”
Maya Gomez, one of the authors of this article and the study, takes photos of transplanted corals off Florida. Jenna Dilworth
Florida’s acroporids have joined the ranks of the California condor – they cannot recover without help. Advancements in microfragmentation and cryopreservation have made it possible to mass produce, archive and exchange genetic diversity at a scale that would not have been possible just 10 years ago. But there is broad consensus that the world must curb the carbon emissions contributing to increased ocean temperatures for restoration to succeed.