Scientists at Scripps Institution of Oceanography at UC San Diego recently participated in a novel National Oceanic and Atmospheric Administration-sponsored expedition to investigate shallow and deep coral ecosystems off the Caribbean island of Bonaire, part of the Netherland Antilles. Multiple underwater robots and divers surveyed one of the most pristine coral reefs in the Caribbean to learn why they remain relatively healthy while many in the Caribbean and around the world are threatened.
The Jan 7-30 mission, which included Scripps Oceanography scientists James Leichter and Dale Stokes, was one of the first in the International Year of the Reef 2008. It is chronicled at: oceanexplorer.noaa.gov.
"The International Year of the Reef is a year-long, worldwide campaign to highlight the importance of coral reef ecosystems, and to motivate people to protect them," said Vice Admiral Conrad C. Lautenbacher, Jr., under secretary of commerce for oceans and atmosphere and NOAA administrator. "NOAA supports this campaign with leadership and coordination, and by sponsoring scientific study of reef systems such as those off Bonaire."
The team collected detailed data on coral species from 5 to 80 meters (16 to 262 feet) depth. Three robots called autonomous underwater vehicles (AUVs) collected detailed bathymetric data and surveyed the "Twilight Zone" of the reefs at depths of 65 to 150 meters (213 to 492 feet). Surprisingly little is known about the reef systems at depths where sunlight is scarce and beyond the range of standard scuba diving.
Through a series of scuba dives, Leichter and Stokes studied the oceanographic variability around Bonaire to provide context for detailed sea bottom surveys. They deployed current meters and unique temperature and pressure-sensing arrays developed in the Marine Physical Laboratory at Scripps. They also surveyed the coral community composition from 5 to 40 meters (16 to 131 feet) at six sites, and down to 80 meters (262 feet) at two sites. Diving below 40 meters (131 feet) involved a specialized technical diving process using a "Trimix" helium-oxygen-nitrogen gas mixture.
At multiple sites Leichter and Stokes also conducted extensive surveys of juvenile corals, sea bottom algae and fish. These surveys have resulted in the most detailed information yet available for assessing the overall condition and "health" of Bonaire's reefs, said Leichter, an assistant professor at Scripps.
"Our findings are interesting, and also distinctly concerning," said Leicther. "Despite the perception and promotion of Bonaire as a site of 'pristine' reefs within the Caribbean, our preliminary analysis shows extensive areas of coral disease and mortality. The pace of development on Bonaire has increased dramatically in the past 5 to 10 years and issues of runoff from land and non-point sources of pollution appear to be quite critical."
But Leichter said there are also some signs suggesting a continued degree of resilience on Bonaire's reefs. Populations of reef-associated grazing fishes are large (Bonaire has enforced a ban on spear fishing since the 1970s) and the researchers documented numerous small colonies of Acropora palmata and some Acropora cervicornis and Acropora prolifera, coral species important in building the frame work of Caribbean reefs that have declined dramatically throughout the Caribbean since the 1970s.
"What we saw opens a number of extremely interesting avenues for future work," Leichter said.
Stokes believes the ecological data they collected is best interpreted in a complete environmental context.
"We need to understand the physical parameters of the reefs as well," said Stokes. "This includes the flow of currents, waves and water temperature affecting the community. Using new instruments developed at Scripps we can rapidly deploy sensors over multiple reef locations and collect fine-scaled data never before seen. This information will aid in the analysis of the changing reef ecology and help the island mitigate its development."
"We believe this is the first science expedition using multiple AUVs to chart Bonaire's reefs and likely the first to do so on coral reefs anywhere," said expedition leader Mark Patterson of the Virginia Institute of Marine Science, College of William & Mary. "This is important because of scale; AUVs obtain wide-area data, allowing scientists to pinpoint further investigation."
Scientists from The College of William & Mary, the University of Delaware and Scripps Institution of Oceanography shared science leadership, while NOAA provided personnel support and funding. NOAA's Undersea Research Center at the University of North Carolina Wilmington provided diving expertise and equipment.
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<p><br /> NOAA Contact:<br /> Fred Gorell<br /> 301-734-1021</p>