In Living Color

New Vehicle Finds Healthy Coral Reefs

By Shelley Dawicki

Source: Woods Hole Currents

Viewed with human eyes through a diver's mask, coral reefs are atrophying, decaying, and sometimes vanishing. Studies and surveys over the past few decades indicate that corals in the Caribbean Sea and around the world are persistently threatened by disease, pollution, and warming waters, leading to widespread coral mortality in the shallows.

But research conducted earlier this year with electronic eyes revealed a major surprise: coral reefs in the deeper waters of the Caribbean appear to be thriving. More than 7,000 images collected by WHOI Associate Scientist Hanumant Singh and Roy Armstrong of the University of Puerto Rico, Mayaguez, showed corals in intermediate water depths to be in much better health and occupying a significantly larger area than previously thought.

Using Singh's SeaBED autonomous underwater vehicle (AUV), researchers conducted a first-of-its-kind study to determine the health of deepwater coral reefs and the related spawning areas of commercial fishing stocks. They carried out nine missions to the Hind Bank Marine Conservation District and South Drop, two reefs located about 10 miles south of St. Thomas and St. John in the U.S. Virgin Islands. Working at night with underwater strobe lights, the team collected high-resolution color images every three seconds at depths of 30 to 80 meters (90 to 265 feet). Taking the AUV below the safe range for scuba diving, the team found extensive reefs nearly 100 percent covered with living corals.

"Until this survey, we did not know what kind of corals we had, how healthy they were, how deep they extended, how large the reefs were, and what lived there because no one had ever seen them," said Graciela Garcia-Moliner of the Caribbean Fishery Management Council, which assisted in the study. "We had nautical charts of the area, but no maps or images. SeaBED has opened a whole new world to us."

Developed by Singh and colleagues in the WHOI Deep Submergence Laboratory, SeaBED can hover over targets like a helicopter and "fly" slowly in shallow to moderate water depths. The vehicle was designed as a small, low-cost imaging platform and as a test bed for underwater docking and other technologies required for future ocean observatories.

Armstrong called SeaBED "the perfect tool for this type of project" because it is cost-effective, and it can be deployed and operated by one or two people in a small boat. The AUV can follow the rugged terrain of a coral reef while working as deep as 500 meters (1,600 feet).

Until now, little information was available on the structure and composition of deeper coral reefs. Most corals need light to survive, so they tend to grow within the top 90 meters (300 feet) of the ocean. Since most divers are limited to the top 30 meters (100 feet), and remotely operated vehicles can snag their cables on the rugged terrain, mid-water corals have largely gone unexplored.

Singh and colleagues plan to return to the reefs with SeaBED in October 2004 with new sensors and a wider survey area. The team is planning annual surveys to determine changes in the health of the reef and its inhabitants.