WASHINGTON — Coral reef ecosystems, among the oldest and most diverse forms of life, are declining in U.S. waters and the Pacific because of overfishing, climate change, marine diseases, land-based pollution, storms and grounded ships.

Such ecosystems "clearly are beset by a wide array of significant threats," the National Oceanic and Atmospheric Administration said in a report yesterday.

About three-quarters of all the threats to coral reefs have not changed since the agency's last overview three years ago. Nearly half of those are considered medium to high threats.

Only in one place, Guam, did a threat level go from low to high, because of coral bleaching from rising ocean temperatures.

Coral reefs provide food and shelter to fish and protect shores from erosion.

"We see a decline in our overall ecosystems," said Mark Monaco, biogeography program manager for NOAA's Ocean Service. "We're very concerned about the future of these delicate ecosystems."

The 522-page report says many of the programs that scientists use to monitor coral reefs only began in the past two to five years, so some of the data are inconclusive.

But the agency's head, Conrad Lautenbacher, said the findings offer "a baseline we can use to compare future results."

The data comes from more than 160 scientists and coral reef managers who have monitored the water quality, the sea floor and fish and other species that live in coral. They also have expanded their digital mapping of shallow water coral reef ecosystems.

Reefs nearest populated areas such as the Florida Keys are under increasing stress, researchers found, while more remote areas such as the Northwestern Hawaiian Islands are doing better.

In Hawai'i, for example, federal officials have removed fishing nets and other debris that had been damaging the reefs and are considering making much of the area off-limits to fishing and other human activities.

"There's a lot of good management going on," said Jeannette Waddell, an NOAA marine biologist, noting that the government is now collecting coral reef data from federal, state, territory and local partners. "Now we can really begin to understand what's out there."

Globally, only about 30 percent of the world's coral reefs are healthy, according to a study last year by 240 scientists in 96 countries. That is down from 41 percent in 2002.

That report listed global warming — blamed for higher water temperatures and carbon dioxide concentrations — as the top threat. It found that the Caribbean had lost 80 percent to 98 percent of its elkhorn and staghorn coral, which are both among the most common species.

Some reef managers also are struggling to combat natural forces, such as coral bleaching, as well as human influences. (Bleaching occurs when warmer seas drive out tiny, one-celled algae that live within the coral and help sustain it.)

Florida Keys National Marine Sanctuary Superintendent Billy Causey said the area suffered two serious episodes of bleaching, in 1997 and 1998, followed by damage from Hurricane George in 1998. The reef lost 30 percent of its living coral as a result.

"The good news is we have not seen an appreciable decline since then. The bad news is we have not seen an increase," Causey said. "Coral reefs are showing the greatest amount of damage in our lifetime compared to any other marine environment."

Sanctuary officials are doing a better job of anticipating strains on the reef, he added, using an early detection system for coral bleaching developed by Mote Marine Laboratory in Sarasota, Fla. They now alert area dive shops that swimmers need to take precautions when the reefs are under stress.

Along with Hawai'i, the Northwestern Hawaiian Islands and Florida, coral reef ecosystems are found in eight other U.S. jurisdictions — the Flower Garden Banks and other banks of the northwestern Gulf of Mexico; Navassa Island southwest of Haiti; the U.S. Virgin Islands; Puerto Rico; American Samoa; the Pacific Remote Island Areas; the Commonwealth of the Northern Marianas; and Guam — and the three nations that make up the Pacific Freely Associated States: the Republic of the Marshall Islands, the Federated States of Micronesia and the Republic of Palau.

The Washington Post contributed to this report.