Woods Hole, Massachusetts, USA — Deep-water coral reefs in the U.S. Virgin Islands may occupy a much larger area and be in better health than previously thought, based on evidence gathered by a new autonomous underwater vehicle that flies through the sea like a helicopter. Woods Hole Oceanographic Institution scientists and engineers used an autonomous underwater vehicle and imaging platform called SeaBED during a first-of-its-kind study to determine the health of deep-water coral reefs and related spawning areas for commercial fisheries.

WHOI scientist Hanumant Singh and colleagues surveyed two reef areas, the Marine Conservation District Hind Bank and South Drop, in June south of St. Thomas and St. John in the U.S. Virgin Islands. Graduate students Chris Roman and Ryan Eustice with postdoctoral investigator Ali Can in collaboration with Roy Armstrong of the University of Puerto Rico and observer Liane Guild of NASA Ames Research Center were participants.

The team used SeaBED, developed by Singh and his WHOI colleagues, to take a series of 7,000 digital still images of the coral reef habitats. SeaBED conducted nine successful missions at night, when it is easier to image the reefs using strobe lights, on Hind Bank near St. Thomas and the South Drop near St. John. Both reefs are 30 to 80 meters below the surface, deeper than normally reachable by divers. The vehicle “flew” seven transects, each several miles long over the banks, collecting color images every 3 seconds during the week-long project. The banks had never been mapped or imaged before, so the diversity and abundance of coral species and the health of the corals was a major surprise. Scientists from the University of the Virgin Islands (USVI), the Department of Planning and Natural Resources of the USVI, and the Caribbean Fishery Management Council (CFMC) also assisted with the study.

While recent reports indicate shallow reefs in the Caribbean and around the world are threatened, this new study found well-developed deeper water coral reefs with nearly 100% living coral cover. This is highly unusual in the Caribbean, they said, where disease, pollution, land run-off, and other factors have caused widespread coral mortality in shallower reefs in the past few decades. Until now, little information was available on the structure and composition of the deeper coral reefs due to the depths of these insular shelf reefs, which are beyond the safe range of scuba diving at 90 to 200 feet deep and some 10 miles from land.

Singh and the WHOI team plan to return to the reefs with SeaBED in October 2004. New sensors may be added and the survey area expanded. Annual surveys are now planned to determine changes over time in the health of the reef and its inhabitants. Keep track at http://www.whoi.edu/.