MIAMI, Oct 16 (Reuters) - U.S. scientists are warning of an environmental threat to deep-water coral reefs after finding they may be just as vulnerable to pollution as their shallow-water counterparts.

For the past three decades, scientists at the U.S. National Oceanic and Atmospheric Administration have observed an alarming decrease in live coral cover on shallow reefs in the Caribbean.

The shallow beds of biologically rich coral are often close to land and were thought to be more susceptible to degradation caused by sewage and other human-related pollutants than deeper, more remote offshore reefs.

In a report published in this month's issue of Continental Shelf Research, however, a team of NOAA scientists said they had documented, for the first time, a pattern of coral loss on a deep-water U.S. Caribbean reef.

The destruction was observed on a reef off St. John in the U.S. Virgin Islands by NOAA scientists using a remotely operated submersible vehicle (ROV) during a sea floor mapping mission in 2005.

"The distribution, status and ecological roles of Caribbean reefs deeper than 30 meters are not well known," NOAA said.

"Using video and pictures taken from the ROV, coral cover decline was estimated at 25 percent. In stark contrast to the typical pattern of coral loss in shallow reefs, the deeper corals were most affected."

Mark Monaco, a marine biologist from NOAA's Center for Coastal Monitoring and Assessment, said the loss of coral on the deep-water reef was especially worrisome because such reefs were traditionally thought to serve as a potential source of regeneration of pollution-depleted shallow reefs.

"Considering the lack of data on deep reefs there is a critical need to map and monitor their condition and investigate possible ecological linkages with shallow reefs," Monaco said.

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