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A team from the St. Petersburg Coastal and Marine Science Center will assist the National Park Service in assessing 2023 heat-stress damage to populations of the threatened elkhorn coral, Acropora palmata.

Bleaching Elkhorn coral in Buck Island Reef National Monument
Shown here is a photograph taken on October 20, 2023, of a wild Elkhorn coral colony in Buck Island Reef National Monument, St. Croix, VI, showing the effects of heat stress caused by elevated ocean temperatures. The heat stress causes “coral bleaching,” or the loss of nutrient-giving microscopic algae that normally live within corals. When these symbiotic microalgae are expelled, the coral’s tissues become transparent and allow the white skeleton to shine through. During bleaching, corals are likely to starve, and may die if ocean temperatures do not cool off to less than about 87 degrees Fahrenheit. Of note in this photo is the bleached appearance of the upper surfaces of the coral, demonstrating the compounding effect of direct sunlight that exacerbates the bleaching—the undersides of this colony that are naturally shaded can be seen still containing some color, and therefore, their symbionts.

Coral reef ecosystems provide essential ecological and economic services to coastal communities—they protect shorelines from storms by acting as natural breakwaters and provide food security through habitat provision for important fisheries. The USGS is continuing research on the coral reefs in Buck Island Reef National Monument (BIRNM) from April 1st through 7th, 2024. The work is jointly funded by the USGS Ecosystems mission area’s National Resource Preservation Program and the Natural Hazards Mission area’s Coastal Marine Hazards and Resources Program.

Ilsa Kuffner, Anastasios Stathakopoulos, and BJ Reynolds (USGS SPCMSC) will join a team from the National Park Service (NPS) led by Kristen Ewen to assess heat-stress impacts to an ongoing coral-growth experiment in BIRBN, a NPS unit off the northeast corner of St. Croix. The group will examine specimens of the threatened elkhorn coral (Acropora palmata) for evidence of heat-stress impacts in an experiment documenting coral-growth rates, and then will likewise survey wild colonies throughout the park. Coral bleaching occurs when ocean temperatures reach and remain above about 87 degrees Fahrenheit. During bleaching, the nutrient-giving microscopic algae that normally live within corals are expelled, and without the symbiotic algae, corals are likely to starve, and may die. In the summer and autumn of 2023, ocean temperatures reached several degrees above this threshold, and many corals in the region bleached and died. In September, the USGS and NPS attempted mitigation of the heat stress by attaching acrylic shades over the experimental corals, so this fieldwork will assess whether that intervention was helpful by comparing the outcomes of corals that were shaded vs. wild colonies living adjacent to the experiment that were not shaded. The overarching goal of this project is to provide NPS managers with the data and information needed to understand the capacity of this coral to grow and calcify in today’s ocean conditions. The project will provide key information needed to assess the feasibility of the coral restoration strategies being developed by the three National Parks and will provide high-quality science to guide these efforts.

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