Florida’s bleached corals get emergency sunshades

Bleached corals Scuba divers attach sunshades on poles to corals that are on cement blocks underwater.
Three scuba divers install shade structures over some bleached corals in Biscayne National Park in Florida on August 18, 2023. The summer of 2023 brought a perilous heatwave to the ocean. The corals here are attached to cement blocks as part of a USGS experiment that provides data on corals throughout the western Atlantic. The shade structures could help reduce light stress on the bleached corals. Image via USGS.

Some bleached corals get emergency relief

Coral reefs around the world are in peril from a number of causes. Oil spills, pollution, storms and increasing temperatures can all endanger corals. The summer of 2023 brought some of the highest sea surface temperatures on record. As more and more corals bleached under the ocean heatwave, some scientists sought to provide shelter for the corals in the form of sunshades.

Erecting sunshades in the Dry Tortugas

On August 13, 2023, three scientists from the St. Petersburg Coastal and Marine Science Center went on a mission to protect endangered corals. The scientists donned wetsuits and scuba gear and entered the waters of Dry Tortugas National Park. There, they found the heat already affecting many of the corals.

The heat drained, or bleached, the corals of their color. Coral can survive bleaching, but they are more stressed and likely to die. Bleaching happens when water temperatures reach 87 F (30 C). In Florida this summer, the sea surface temperatures not only hit 87 F, they hit the 90s for extended periods of time, even cracking the 100-degree mark. And it wasn’t just Florida that had high sea surface temperatures, but many places around the globe.

The scientists constructed nearly 40 temporary sunshades over corals in the Dry Tortugas. How would an underwater sunshade help? Ilsa Kuffner, a USGS research marine biologist who participated in the emergency procedure, said:

The shading helps by reducing the sun’s rays. While normally corals need sunlight for their symbionts to photosynthesize, when they are bleached, the sun’s energy instead causes a lot of stress.

The sunshades weren’t the only measure the scientists used in their attempts to save the coral. In addition to the sunshades, the team also spent several evenings adding dim lights to the shaded coral in an effort to attract prey for the coral to feed on.

Other corals also got sunshades

After working in the Dry Tortugas, the scientists went to work in Biscayne National Park. With the help of two more scientists, they erected sunshades there as well. Kuffner said:

The catastrophic ocean-heat wave that is occurring in Florida and spreading quickly to the rest of the western Atlantic and Caribbean presents a huge risk to the health and future of coral reef ecosystems.

The scientists focused on the threatened elkhorn coral for their rescue missions. Elkhorn coral does indeed resemble an elk’s antlers. It’s one of the most important corals in the Caribbean because of the complex habitat it provides marine life and its ability to protect the shoreline from waves and storms. Following a disease in the 1980s, only 3% of elkhorn corals are left. The elkhorn coral were part of an assisted migration experiment, where corals grown on a farm were reintroduced to the national parks. As Kuffner said:

While we know we cannot save every coral; we are focusing on individual corals that represent unique genetic lines that are thought only to exist in certain National Parks.

Whether the corals survive until the cooler temperatures of fall remains to be seen.

Bleached corals: A white coral feet with a makeshift shade from 4 legs and a board for a roof.
The ocean heatwave during the summer of 2023 put many coral reefs under stress. In this image from August 15, 2023, a bleached coral in Florida’s Dry Tortugas gets emergency relief in the form of shade to help reduce light stress. Image via USGS.

Bottom line: Scientists constructed sunshades over bleached corals in two of Florida’s national parks in an effort to protect them from further damage.


September 21, 2023

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