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.
“The Keys have not seen a cold-water bleaching event like this since the winter of 1977-78, when acres of staghorn coral perished,” said Dr. Billy Causey, southeast regional director of NOAA’s Office of National Marine Sanctuaries. “But today we are better prepared to document and assess the impacts of stress thanks to numerous partners.” Causey has lived and worked in the Keys since 1971.
Over the next two weeks, teams of science divers from federal and state agencies and non-governmental and academic organizations will be surveying sites from the Dry Tortugas through Martin County to assess and monitor mortality and changes in coral health. The site locations and survey protocol were developed by The Nature Conservancy and other members of the Florida Reef Resilience Program for monitoring impacts to corals following a major disturbance, such as a mass-bleaching event.
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.
“If there is any ‘good news’ it’s that reef managers and scientists are able to quickly respond to this event and are in a good position to learn more about how reefs will rebound following such a rare occurrence,” said Chris Bergh, director of The Nature Conservancy’s Coastal and Marine Resilience Program.
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.
Mote Marine Laboratory BleachWatch Coordinator Cory Walter was surprised at the extent of the affected corals during the first surveys following the cold weather on Jan. 20-21. “We saw a lot of very recent mortality, especially on the mid-channel and nearshore reefs,” she said. “The cold seems to have affected all species equally, though we’ll know more after we get reports from this wider monitoring effort. The offshore reefs seemed to be faring better.”
Mote’s surveys took place from nearshore of Summerland and Big Pine keys south to Looe Key Reef. Monitoring efforts are being coordinated by The Nature Conservancy in partnership with Mote, Florida Keys National Marine Sanctuary, as well as the National Park Service, Florida Department of Environmental Protection, Florida’s Fish and Wildlife Conservation Commission, the University of Miami and Nova Southeastern University.
Divers in the Florida Keys are encouraged to report the location of observed coral bleaching to Mote Marine Laboratory’s BleachWatch program at www.mote.org/bleachwatch. This early-warning network helps alert managers to major disturbances. 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).
source: The Nature Conservancy