DRY TORTUGAS NATIONAL PARK, Florida (Reuters) -- In the azure waters of Florida's remote Dry Tortugas National Park, corals have been toppled by hurricanes and blighted by disease and a phenomenon known as bleaching.
Eight hurricanes in two years and a plague of disease that swept the Caribbean recently have damaged the colorful, thick carpets of open-water coral reefs in the 100-square-mile park off Florida's southwest coast.
With another hurricane season under way and diseases such as white plague getting an early start this year, scientists surveying the reef expressed heightened concern for the fragile corals, which are important nurseries and habitats for marine life and harbingers of the health of the seas.
"There are some areas out here that are like a parking lot, absolutely denuded," said Dr. Jerry Ault, associate professor of marine biology and fisheries at the University of Miami's Rosenstiel School of Marine & Atmospheric Science.
Ault supervised a team of nearly 40 divers aboard the 100-foot research vessel Spree recently as they conducted a three-week, $300,000 biennial census, surveying coral, fish and lobster.
The Dry Tortugas are a cluster of seven tiny islands and acres of coral seabed located 70 miles southwest of Key West, a popular tourist island at the southern tip of the Florida peninsula.
"Since 2004, we have had eight storms that have tracked within 100 miles of the Tortugas," said Ault. "In 2005, this was ground zero for major storms.
"Are we afraid of another hurricane season? Three (bad) hurricane seasons can't be a good thing."
Researchers are sounding dire warnings about the health of the world's coral reefs. The reef running alongside the 110-mile Florida Keys island chain is North America's only barrier reef and the world's third longest.
The Tortugas Ecological Reserve was created in 2001 by the Florida Keys National Marine Sanctuary as the largest U.S. permanent reserve where all fishing and removal of coral is banned. At the time, it was considered to contain some of the nation's healthiest coral.
But 10 percent to 12 percent of the corals surveyed appear to be diseased compared to only 1 percent to 2 percent in 2001, said researcher Dione Swanson.
The affected corals include star, brain, elkhorn and staghorn corals, the primary reef builders critical to the health of the habitat.
"It looks a lot like white plague, and it's an early start for this disease, which we usually see in August or September. Last year was a high bleaching year," Swanson said. "We're seeing a lot of coral colonies overturned."
Coral bleaching, a malady that has swept Florida, Caribbean and Australian reefs in the last year, whitens and weakens coral and is blamed on unusually warm water that some scientists attribute to global warming.
Another ominous sign, said Swanson, is the state of the Sherwood Forest reef tract. Once a thickly carpeted reef estimated to be about 9,000 years old, it "has a lot of dead colonies," she said.
Gorgonians, or sea fans, have been hard hit by two years of hurricanes, Ault said.
"The gorgonian population has been reduced. In some areas, it's scrubbed like a Brillo pad."
The implications are not just environmental but also economic. In South Florida, the reef and its ecosystem is a $6 billion annual business, according to Ault. It lures divers, recreational and commercial fishers and sports tourists.
Craig Bonn, a biologist with the Dry Tortugas National Park, estimated only 13 percent of the coral that used to exist in the Keys remains. "Corals are in trouble all over the world," he said.
White plague disease can be linked to poor water quality and bacteria caused by human activity, said researcher Mark Chiappone.
In the 1980s, acropora coral, a colorful hybrid species of staghorn and elkhorn coral, was plentiful, said Dave Score, superintendent of the sanctuary, which protects 2,900 square nautical miles of marine habitat stretching from the Dry Tortugas to Biscayne National Park off Miami. "Now you can't find it."
The U.S. National Oceanic and Atmospheric Administration has listed staghorn and elkhorn coral as threatened under the Endangered Species Act. The designation is expected to prompt new regulations and restoration efforts.
Reef Relief, a non-profit Florida Keys environmental group, began warning of the reef's demise in 1987. It blames the damage on a lack of effective federal protection, global warming, agricultural pollution runoff from the Florida Everglades and cruise ship sewage.
"I'm so frustrated. It's unbelievable that this coral has disappeared. The people managing this never do anything meaningful," said DeeVon Quirolo, executive director of Reef Relief, who said that only 2 percent of the reef in the Florida Keys is covered with live coral.
"Coral reefs are in a state of decline around the world," said Billy Causey, acting regional manager for national marine sanctuaries in the southeast United States. "At least we have protections in place. There's probably not a piece of coral reef real estate that is any more protected."