Winter is not coming: Simulating heat stress on Florida’s Coral Reef

Coral reefs are increasingly threatened by rising sea temperatures, pollution, and overfishing, with ocean warming being a major driver of mass bleaching. Florida’s Coral Reef (FCR), the northernmost reef system in the Caribbean, was severely impacted during the Fourth Global Coral Bleaching Event (GCBE4) in 2023, with extensive bleaching recorded at most monitored sites, including those of the Mission Iconic Reefs (MIR) restoration project. This study uses the multiscale baroclinic ocean model SLIM3D with a horizontal resolution reaching 100 m over coral reefs, to reproduce oceanic and thermal conditions during the 2023 bleaching event and to investigate spatial variability in bleaching severity. Thermal stress was assessed using the Degree Heating Week (DHW) metric, which represents the cumulative intensity and duration of heat stress above bleaching thresholds. DHW patterns were analyzed alongside local circulation patterns, vertical mixing, and stratification outputs. Results show a marked inshore–offshore contrast, with offshore reefs generally experiencing lower heat accumulation and higher temperature variability due to persistent mixing and occasional cold-water intrusions, while certain nearshore sites displayed increased DHW linked to persistent stratification and reduced mixing. Within the MIR network—selected for their ecological diversity, productivity, and geographical variability—this spatial variability translated into contrasting bleaching conditions: for instance, inshore reefs such as Cheeca Rocks recorded some of the highest DHW values, while others, including Horseshoe Reef, exhibited comparatively lower DHW despite being only 40 kilometers apart. These differences were influenced by topography, local circulation patterns, vertical mixing, stratification changes, and cold-water upwelling. Our findings highlight the role of ocean dynamics in modulating coral bleaching impacts and in identifying potential thermal refugia. Incorporating high-resolution hydrodynamic modelling into restoration planning could help prioritise sites with a higher capacity to withstand future marine heatwaves, thereby enhancing the long-term resilience of restoration efforts in the FCR.

Affiliations

UCLouvainSST/ELI/ELIE - Environmental Sciences

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Rycx Lamme d’Huisnacht, L., Dobbelaere, T., Scherpereel, C., Hirsh, H., Lambrechts, J., & Hanert, E. (2026, February 25). Winter is not coming: Simulating heat stress on Florida’s Coral Reef. Ocean Sciences Meeting 2026 - Glasgow OSM26, Glasgow - Ecosse. https://hdl.handle.net/2078.5/277162