“What we’re seeing is that there is not a universal response to this temperature stress. It’s not all exactly the same. There are places where we see resilient communities of coral, resilient individuals, resilient parts of the reef. And we need to try to understand what it is about that genotype, that species, or that place, and use that information to inform as we continue the restoration work.” 

-Sarah Fangman, Florida Keys National Marine Sanctuary Supervisor

NOAA Coral Reef Watch’s daily 5km satellite coral Bleaching Alert Area (BAA) for Florida from May 16, 2023 to October 31, 2023, shows the approach of the severe heat stress in Florida, and its eventual dissipation.  Credit: NOAA Coral Reef Watch / Senior Scientist, Oceanographer, and Chief Product Developer Dr. Gang Liu

This map depicts predicted marine heatwave conditions in September 2023 as generated by the Physical Sciences Laboratory’s experimental forecast model. Credit: NOAA Physical Sciences Laboratory.

When the region’s longest-ever recorded marine heatwave threatened to devastate the reefs and broodstock raised for restoration efforts,  the network of managers, researchers, conservation and restoration practitioners, aquarists, and engaged citizens mobilized to monitor, research, and respond. Four focal points were identified.

1. PROTECT ESTABLISHED RESTORATION INVESTMENTS/EFFORTS
To reduce stressors that could be controlled, overall management efforts for in-water coral nurseries and outplant sites – such as cleaning structures and culling diseased coral fragments to prevent spread –  were proactively amplified. As the water got hotter, Mission: Iconic Reefs partners incorporated bleaching threshold data into their adaptive management plans and voluntarily scaled back in-water nursery outplanting.

On July 21, 2023, Florida Fish and Wildlife Conservation Commission and Florida Keys National Marine Sanctuary released “Interim Protocols for Management of In-Water Nurseries, Coral Transport and Coral Outplanting” for the summer and fall of 2023. Transport limitations, and temperature and disease thresholds in nurseries and at outplant sites were established.

2. ADAPTATION RESEARCH

Despite being one of the primary foundational species that build Caribbean reefs, Acropora is one of the most thermally-sensitive coral species in the world that hosts only one non-heat-tolerant symbiont (NOAA Coral Reef Watch Coordinator Dr. Derek Manzello). With ocean temperatures on the rise, Mission: Iconic Reefs research to identify higher-temperature-tolerating Acropora genotypes continues to be a high priority. With the assumption that unique genetic adaptations supported their survival, corals propagated from species genotypes collected from or directly reared in stressful conditions are being used for outplanting with the hope that these new genetic strains jump-starts the productivity of the reef and increases new genetic crosses and its ability to resist and/or recover from future coral bleaching events. Ac

3. GENETIC PRESERVATION

In mid-July, NOAA and Mission: Iconic Reefs partners pulled together for the Herculean effort of EVACUATING CORAL BROODSTOCK FROM IN-WATER NURSERIES for temporary safekeeping until waters cooled. Some were moved to a TEMPORARY SPECIAL USE AREA, protecting 2,800 coral fragments in 70 feet of water.

Replicates of all known living fragments of elkhorn and staghorn coral (species listed as threatened under the Endangered Species Act) were collected and transferred to land-based living gene banks.

Florida Institute of Oceanography’s Keys Marine Lab in Layton, Florida served as a staging area, holding rescued corals in temperature-controlled tanks before being loaded into the Coral Restoration Foundation’s “coral bus” for shipment to The Reef Institute or transported to Mote’s Gene Bank by The Florida Aquarium. Corals from nurseries at the University of Miami and Nova Southeastern University were also transferred there.

4. MONITOR TO IDENTIFY RESILIENT AREAS, HABITATS, REEFS, AND COLONIES

Data from August 2023 and February 2024 cruises will help NOAA biologists understand the full extent of the marine heatwave impacts and inform future Mission: Iconic Reefs restoration strategy. Variables include: outplant method, temperature trends, bleaching thresholds, site comparisons, and survival and mortality rates by age and outplant dates.

During the height of the marine heat wave, the Mission: Iconic Reefs Stewardship and Monitoring Team conducted a 10-day assessment at segments of all SEVEN ICONIC REEF SITES to document the condition of outplanted corals. There were eight additional weeks of abnormally high temperatures after the survey was conducted.  

PRELIMINARY OBSERVATIONS

• • • • • • • Approximately 30% of outplanted staghorn and 45% elkhorn coral died– likely due to the heat stress
            • Approximately 90% of elkhorn and staghorn coral exhibited heat stress
            • Fully bleached and recently dead corals were observed in every location 
            • Partially bleached pockets of corals were observed at most sites
            • Some completely unbleached corals were observed
            • Boulder corals showed much less bleaching and minimal mortality as compared to the branching elkhorn and staghorn corals.