Cold temperatures causing coral bleaching
in South Florida and the Keys

Sustained cold water temperatures in South Florida and the Florida Keys triggered severe coral bleaching and even coral death, alerting resource managers and prompting a coordinated assessment response from the science and scuba diving communities. Temperatures in some nearshore areas of the Florida Keys National Marine Sanctuary dropped to 52 degrees Fahrenheit for several days — well below average for this time of year — with fatal results for some corals.

A cold-water bleaching and die-off hasn’t occurred in Florida since the late 1970s.

Coral bleaching occurs when a coral animal undergoes stress and loses its symbiotic algae (called zoxanthellae). Prolonged stress can result in coral death. Coral bleaching is most frequently associated with elevated water temperatures, but stress also occurs when water temperatures dip below the preferred 60-degree threshold.

Typically, the Florida Reef Resilience team comes together for surveys following warm-water bleaching events. Activating the team now will provide valuable insights on what happens to corals when they get too cold. Monitoring needs to be implemented as quickly as possible, because macroalgae and cyanobacteria quickly invade or overgrow dead coral and could make identifying recently deceased corals difficult.

Divers should also be aware that bleached corals are extremely vulnerable to additional stress. Divers are encouraged to seek non-stressed areas to enjoy at this time and, as always, to pay careful attention not to touch corals.

The coral reefs of the Florida Keys are the basis of a unique and diverse ecosystem that forms the third largest barrier reef in the world. Reef-related expenditures generate more than $4.4 billion annually in southeast Florida and reef recreation supports more than 70,000 jobs (2001).
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