Mapping the Spatial Distribution of Disease Affecting Elkhorn Coral within Virgin Islands National Park: A Closer Look at an 'Endangered' Reef-building Species

Rogers, Caroline; Muller, Erinn; Devine, Barry; Nieves, Pedro

Over the last three decades, the most significant decline in shallow coral reefs in the Caribbean, including those in Virgin Islands National Park, St. John, was the dramatic loss of elkhorn coral (Acropora palmata). In the 1960s and 1970s, elkhorn coral was the main reef-building coral at depths of less than 10m in the US Virgin Islands (USVI), growing in nearly mono-specific stands on the reef crest and in the upper and lower forereef zones of well-developed fringing and bank barrier reefs and on isolated patch reefs. This species is a critical structural component that provides essential habitat for fish and other organisms. In the mid-1970s and 1980s, white band disease (WBD) and hurricanes caused dramatic declines (in some cases over 90%) in A. palmata (Gladfelter 1982, Rogers et al. 1982, Aronson and Precht 2001) not only in the USVI but throughout the Caribbean. These corals were responsible for the overall physical structure of these reefs. Their loss dramatically changed the nature of the reefs and had undocumented effects on associated reef fishes and other organisms, such as endangered hawksbill turtles that use the reefs for shelter and feed on reef organisms. This regional loss of Acropora palmata (and A. cervicornis) was the most dramatic change to occur on Caribbean reefs in the last 30 years, and both species are now being proposed for listing as "threatened" under the Endangered Species Act (Diaz-Soltero 1999, Bruckner 2002, NOAA Federal Register March 18, 2005). There is now limited evidence that elkhorn coral is increasing in abundance at sites in the USVI, although no reef sites that have been examined have as much elkhorn coral as in the 1970s. Elkhorn coral appears to be recovering slowly within Virgin Islands National Park and on other St. John reefs, but white band and white pox disease may delay or even prevent this recovery. The objective of this project is to map elkhorn reefs within the park using a GPS unit to record the number of living colonies, their size distribution, and the prevalence of white pox and white band disease.