By Michael Christie
FORT LAUDERDALE, Florida (Reuters) - Half of U.S. coral reefs are in poor or fair condition, threatened by climate change and human activities like sports fishing, shipping and the release of untreated sewage, a U.S. government report said on Monday.
Reefs in the Caribbean, in particular, are under severe assault and coral in the U.S. Virgin Islands and off Puerto Rico had not recovered from 2005, when unusually warm waters that led to massive bleaching and disease killed up to 90 percent of the marine organisms on some reefs.
"The evidence is warning us that many of our coral reef ecosystems are imperiled and we as a community must act now," said Kacky Andrews, program manager of the Coral Reef Conservation program at the National Oceanic and Atmospheric Administration.
The new NOAA report on the state of coral reefs in the United States and Pacific territories, including Palau and Guam, was presented at a meeting of coral reef scientists in Fort Lauderdale, Florida.
It was the third such report and the second to be based on actual monitoring of reefs. The reefs were classified as excellent, good, fair or poor based on such things as water quality, fish population and the threats they faced.
The last report was issued in 2005 when warm Atlantic waters killed off large swaths of coral through bleaching, a condition that occurs when environmental stresses, like heat, break down the symbiotic relationship between coral polyps and unicellular algae that give them color.
Half the coral reefs off the U.S. Virgin Islands and Puerto Rico were killed that year, said Jenny Waddell, a marine biologist at NOAA's Center for Coastal Monitoring and Assessment. On some reefs, the fatality rate reached 90 percent, she said.
A series of powerful hurricanes also devastated coral reefs off the Florida Keys in 2005.
But scientists at NOAA said coral reefs had been suffering for much longer due to a warming climate and other "stressors," many due to human activity, such as overfishing and damage caused by ship anchors.
"It is important to note that these declines did not happen overnight, they did not happen during the last three years," said Andrews.
"The degradation has happened over the past several decades and recovery may require similar time frames. Although there are a number of measures that we can implement in order to promote conservation, there are no quick fixes."
The NOAA report was based on reef monitoring in 15 areas in the Atlantic and Pacific.
It said that reefs near populated areas tended to suffer more intense threats due to coastal development and recreational activities like boating, diving and fishing, but even remote reefs were affected by climate change.
Reefs in the vast Pacific Ocean tended to be more resilient, with a greater diversity of both coral and fish, NOAA scientists said. While Pacific reefs had been able to start recovering from worldwide bleaching in 1998, Caribbean reefs had not.
Human activity had not just left Caribbean reefs battered, but also pretty tame in terms of marine life, said Alan Friedlander, a NOAA marine biologist based in Hawaii.
"When you dive in remote parts of the Pacific you really feel like an intruder, like you don't belong there and the big guys let you know. You feel way down the food chain," he said.
(Editing by Cynthia Osterman)