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September 7, 2023

Coral provide shelter for many marine species and directly support most of Florida’s multibillion dollar recreation and fishing industries. They also provide coastal communities shoreline protection from storms and waves by helping to break up waves and dissipate energy.


Bleached white Elkhorn coral shown under a shade cover installed to protect it in Dry Tortugas National Park, Pulaski Shoal
Shown here is a colony of the threatened Elkhorn coral that has become "bleached," that is, lost all its algal symbionts because of the summer 2023 ocean-heat wave.  USGS photo by Ilsa Kuffner.

Coral reefs are a critical natural resource providing coastal communities protection from storms by helping dissipate wave energy. Corals also provide shelter for many marine species.

Three USGS scientists from the St. Petersburg Coastal and Marine Science Center traveled to Dry Tortugas National Park August 13 to erect temporary shade structures in hopes they would lessen the effect of the sun’s rays and help the corals survive until the fall, when water temperatures traditionally drop. When experts arrived at the park, they found much of the corals had lost their color: they were bleached.

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, called zooxanthellae, corals are likely to starve, and may die.

“The shading can help by reducing the sun’s rays,” said Ilsa Kuffner, a USGS research marine biologist who helped lead efforts to save corals in Florida in August. “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 team spent several days doing emergency fieldwork adding nearly 40 temporary shade structures to corals located inside Dry Tortugas National Park. They then moved to Biscayne National Park where two more USGS scientists joined in the effort and the team was able to shade additional corals.

In Dry Tortugas National Park, the team took an additional life-saving measure in attempts to feed the corals. Several evenings during the emergency mission, the team added dim lights to the shaded coral in hopes of attracting prey for the coral to feed on.

“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,” Kuffner said.  

USGS work like this provides science to guide the management and restoration of the threatened Elkhorn coral. Because of coral bleaching, these threatened corals are in jeopardy of complete devastation, which is why the USGS partnered with the National Park Service on this rescue mission.

“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,” Kuffner said.

This unprecedented early-season coral bleaching event is not unique to Florida, and there are still many more corals at risk. Kuffner is hopeful that the measures taken can assist the now-shaded corals survive until cooler water temperatures in the fall.

To learn more about USGS coral research, visit:

Information on how coral reefs protect coastlines:

More about Elkhorn coral growing in Dry Tortugas National Park:

Divers putting shades over experimental Elkhorn corals in Biscayne National Park
Three USGS scientists install shade structures over experimental Elkhorn corals that have become "bleached," that is, lost all their algal symbionts because of the summer 2023 ocean-heat wave. The corals are attached to cement blocks as part of the U.S. Geological Survey’s Coral Assessment Network that provides data on coral-growth rates throughout the western Atlantic. USGS photo by Ilsa Kuffner. 

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