Communications & Outreach Working Group: Florida Bleaching Summary, September 2025

OVERVIEW

Corals rely on microscopic algae called zooxanthellae, which live within their tissues, give corals their color, and supply up to 90% of their nutrition. When heat stress forces corals to expel their algae, their white calcium carbonate skeletons become visible, a process called coral bleaching. In addition, coral bleaching results in the depletion of corals’ energy stores and makes them more susceptible to other stressors. When bleaching lasts for an extended period of time or consecutive years, corals may die from starvation and or the heat stress alone, as seen in 2023.

During the 2023 marine heatwave, also part of  the 4^th global coral bleaching event, Florida’s Coral Reef experienced the most severe coral bleaching to date. Cumulative heat stress in the Florida Keys was nearly three times the previous record from 2015/2016. Surveys found severe bleaching prevalence in Biscayne National Park south to the Dry Tortugas. Averaged across transects from Biscayne, Upper Keys, Middle Keys, and Lower Keys subregions, mean coral colony abundance decreased by 21%; 2024 post-bleaching surveys found a 74% decline in Agaricia species, a 47% decline in branching Porites spp., and a 47% decline in P. astreoides, averaged across the reef zones. Staghorn and elkhorn coral were disproportionately affected. In addition, while Southeast Florida reefs were heavily impacted, many coral reefs and patch reefs in the northern region fared well.

So far this year, localized bleaching and paling has been reported in the Keys, paling has been reported in the Miami area, and moderate bleaching in Broward County. Disturbance Response Monitoring surveys began in August and when complete, the report will provide a more robust understanding of current bleaching.

Overall, bleaching is not a death sentence, and short-term coral paling and bleaching do not generally lead to coral mortality. However, bleaching does signal coral stress, making the monitoring of bleaching vital for understanding reef health and applying adaptive management to Florida’s planning and restoration efforts. Integrating monitoring with targeted intervention strategies also strengthens resilience based action plans, ensuring a more informed and effective response to ensuring the resilience of Florida’s Coral Reef.

HOW YOU CAN HELP

Make a bleaching report! The Florida Department of Environmental Protection (FDEP) has a reporting tool at SEAFAN.net or you can call the hotline 866-770-7335. Community scientists can report bleaching under “Report a Marine Incident”; trained individuals can report bleaching in the Keys through the Florida Keys BleachWatch or in Southeast Florida through FDEP’s South Florida BleachWatch. Reports of no bleaching are just as important so scientists can track where bleaching is not occuring.

FLORIDA’S RESPONSE

Since 2023, Florida has gathered insights and lessons learned from practitioners, managers, and other partners on ineffective and effective bleaching response strategies. Folks are taking these lessons learned and applying some of the below strategies in preparation for, and response to, potential coral bleaching:

• Focusing restoration activities on more boulder coral species.
• Pausing outplanting and restoration activities during times of thermal stress.
• Monitoring coral conditions to better understand processes of bleaching and patterns of resilience in the system and learning from corals that survive bleaching events for restoration planning.
• Ensuring experimental activities to mitigate bleaching are put into permits ahead of time.
• Using corals that have been shown to be more thermally tolerant for sexual reproduction.
• Trialing the outplanting of thermally tolerant corals from other counties with coral from Florida.
• Monitoring real-time sea surface and bottom temperatures at key reef sites and coral nurseries.
• Preparing land based facilities to accept corals from in-water nurseries, should evacuations be necessary. The focus of any evacuations will be the preservation of coral genetic diversity.
• Utilizing in-water nurseries at deeper depths for short periods of time, where impacts from temperature and light are less pronounced.
• Shading existing in-water nursery structures to reduce the impacts of temperature and light.
• Removing known coral predators and competitors, like corallivorous snails and macroalgae, from reef sites and coral nurseries.

The FDEP SEAFAN network reporting tool can also be used to report stony coral tissue loss disease, another lethal disease of unknown origin that has been infecting stony corals since 2014.  In the Caribbean, the Diadema Response Network needs reports of healthy or dying long-spined sea urchins, submit your reports here.  Call Shelly Krueger, Florida Sea Grant agent in the Florida Keys for the University of Florida IFAS Extension, Monroe County at 305-292-4501 to file a report or for more information.

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