Nearly half of the U.S. coral reef ecosystems are considered to be in "poor" or "fair" condition according to a new analysis of the U.S. National Oceanic and Atmospheric Administration, or NOAA.  The report was presented during the 11th International Coral Reef Symposium in Fort Lauderdale, Florida this week.  Producer Zulima Palacio looks into the new report on the eve of the International Year of the Reef 2008.  Jim Bertel narrates the story.

Scientists often call beautiful and healthy coral reefs like this one the largest living structures on earth.  However, they are being replaced by this: bleached, diseased and dead coral.

Mark Eakin, the coordinator of Coral Reef Watch for the U.S. National Oceanic and Atmospheric Administration, (NOAA), says three years ago a rise in sea temperatures in the area of the U.S. Virgin Islands in the Caribbean killed about half of the remaining coral. 

"The level of thermal stress, the heating that caused that bleaching in 2005, was greater that the previous 20 years of satellite record combined," Eakin said.

Eakin says NOAA studies have identified two key factors in the process of coral destruction.

"We believe about a two degree increase Celsius, greater than what we have seen over the last 100 years, will be a critical level for coral reefs," Eakin said. "In addition the increase in atmospheric CO2 [carbon dioxide] not only causes an increase in temperatures but it also changes the chemistry of the oceans.  It drops the pH [measure of acidity and alkalinity] and makes the ocean more acidic."

The latest U.S. report serves as a new warning of the effect of global warming in the oceans.  It says that the nation's coral reef ecosystems, particularly those close to populated areas, continue to face intense threats from human activities such as fishing, sedimentation and recreation.

"Coral reefs are in some ways a canary in the coal mine," says Jeannette Waddell, a marine biologist at NOAA.  "They are extremely sensitive to changes in their environment."

Scientists sometimes refer to coral reefs, the most diverse marine ecosystems, as the rainforests of the ocean.  And they say there are more fish around reefs than in remainder of the oceans. 

And there is more at stake.  Doctors say coral reefs are also a source of medicine.  

"We are maybe losing species that hold enormous promise for human suffering, for relieving human suffering and preventing human death," says Dr. Eric Chivian, who is with Harvard Medical School.

Reports say growing concentrations of carbon dioxide and pollution, warming of ocean waters as well as  disease, overfishing and damage from fishing nets are part of the problem.  Eakin also expressed concerns about the speed of change.

"We are seeing increases in temperature at rates that we haven't seeing any time in the last several hundred thousand years.  So, the problem here is that while corals can adapt, we don't see any evidence that they are going to be able to adapt quickly enough to respond to these rapid changes," Eakin says.

The new report on the state of U.S. coral reefs finds conditions similar to other regions.    Scientists estimate that at least 30 percent of the world's coral reefs are already dead.  They also say that human activities harm not only the reefs, but also mankind.