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U.S. GEOLOGICAL SURVEY

Coral Diseases Following Massive Bleaching in 2005 Cause 60 Percent Decline in Coral Cover and Mortality of the Threatened Species, Acropora Palmata, on Reefs in the U.S. Virgin Islands

By Caroline S. Rogers

Severe Bleaching in 2005

Record-high seawater temperatures and calm seas in the summer of 2005 led to the most severe coral bleaching (greater than 90 percent bleached coral cover) ever observed in the U.S. Virgin Islands (USVI) (figs. 1 and 2). All but a few coral species bleached, including the threatened species, Acropora palmata. Bleaching was seen from the surface to depths over 20 meters.

Disease Outbreak

With cooler temperatures in October, some corals began to regain their color. However, many corals then died partially or totally in a regional disease outbreak (Miller and others, 2006). U.S. Geological Survey (USGS) and National Park Service (NPS) scientists collaborated to increase the frequency of monitoring at five reefs, four of them within Marine Protected Areas, Virgin Islands National Park and Buck Island Reef National Monument (fig. 3). The effects of disease, primarily white plague, were recorded along permanent, randomly selected long-term transects maintained by the NPS South Florida/Caribbean Inventory and Monitoring Network (fig. 4). The number and size of disease lesions on each coral colony within one meter on either side of each transect were quantified (fig. 5). Effects of bleaching and disease on A. palmata colonies were followed at shallower reefs monitored by USGS.

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