January 2010 Cold-Water Event Damages Florida Patch Reefs

Study results suggest this was the worst cold-related coral mortality on record.

 Before and after showing cold weather damage
Before (top) and after (bottom) photos
illustrate the January 2010 cold-water
event's damaging effect on patch reef
coral communities in the Florida Keys.

Florida’s nearshore coral reefs are an important component of the greater Florida reef tract and home to a variety of marine species. These patch reef communities thrive in shallow waters near the Florida Keys and have demonstrated resilience to environmental stressors, including disease and temperature fluctuations. While widespread coral bleaching and mortality are commonly associated with warm-water disturbances, an extreme cold-weather event revealed these tropical species are also vulnerable to prolonged cold-water exposure.

In January 2010, an intrusion of Arctic air across the southeastern United States and Gulf of Mexico caused one of the coldest 12-day periods on record in the Florida Keys. This historic event caused water temperatures in shallow, nearshore areas to drop below the lethal limit for many tropical species for several consecutive days, resulting in coral die-offs.

In February 2010, FWRI scientists surveyed four patch reefs to assess the damage. Compared to observations from summer 2009, scientists discovered the unusually cold water temperatures harmed many coral and other bottom-dwelling species. Overall, they observed a nearly 50 percent reduction in cover of soft, fanlike octocorals and a nearly 40 percent loss of hard, stony corals. Scientists concluded sites with the longest exposure to extremely cold temperatures experienced the greatest coral loss.

View before and after photos in the Florida Keys 2010 Cold-Water Event Flickr set.

Unlike offshore bank reefs where temperatures are regulated by ocean currents, shallow-water patch reefs are subject to large variations in temperature. Since 1996, scientists working on the Coral Reef Evaluation and Monitoring Project have documented how large-scale and localized disturbances affect reefs in the Florida Keys. They believe the regular exposure to a wide range of temperatures increases patch reefs’ tolerance to fluctuating conditions; however, water temperatures during the 2010 winter event were far below the lethal limit for many coral species. The widespread mortality associated with the January 2010 event was especially alarming because patch reefs had survived numerous disturbances that caused extensive damage to other reef communities. As a result, scientists concluded this cold-weather event was one of the most severe on record.

Patch reefs are regarded as critical to the resilience of the greater Florida reef tract because they provide habitat for various organisms, supply larvae to offshore reefs and have demonstrated resistance against previous disturbances. It is unknown whether these patch reef communities can recover from such a catastrophic event, and scientists will use the data collected at the four sites as a baseline from which they can monitor recovery.

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