Regional Monitoring of Coral Condition in the Florida Keys

Tropical reef corals have experienced unprecedented levels of bleaching and disease during the last three decades. Declining health has been attributed to several stressors, including exposures to elevated water temperature, increased solar radiation, and degraded water quality. Consequences of coral bleaching and disease vary; some recover, while others lose tissue, die, and succumb to algal overgrowth. In 2000, a regional monitoring project documented disease prevalence and bleaching across 41 km2 of coral reefs in the Florida Keys. Thirty sites were randomly selected from a spatially-balanced grid. A radial belt transect (113 m2) was surveyed at each site and 100-300 colonies were encountered in each transect. The coral species and health status was recorded for each colony. No site had greater than 13 percent disease prevalence and ~80 percent of the reef area had <5 percent disease prevalence. The survey will be repeated in 2005, but with additional measurements to estimate colony size, percent living tissue, and living surface area. These added endpoints are expected to provide information on the consequences of bleaching, disease, and other stressors on coral communities. Data will be compiled to characterize community composition, abundance, age class structure, and survival of different species across the Florida Keys reef tract. During a pilot study in 2003, living coral tissue on large colonies of elkhorn coral Acropora palmata was considerably less than on small colonies, possibly indicating a major mortality event (for example, hurricane or bleaching) that occurred prior to recruitment of the smaller colonies.