for National Geographic News
Caribbean coral reefs are dying from disease at an alarming rate, according to scientists who monitor the ocean ecosystems.
Researchers say they have yet to gauge the full extent of the die-off. But at monitoring sites in the U.S. Virgin Islands more than 90 percent of the coral suffered bleaching.
Caribbean coral was weakened by unprecedented bleaching events following record warm water temperatures last year.
Bleaching occurs when heat stress causes corals to expel their symbiotic, food-producing algae known as zooxanthellae, turning the reef's skeleton ghostly white.
While coral can recover from bleaching events, many weakened Caribbean reefs are now succumbing to a fatal coral disease known as white plague.
Average water temperatures in the eastern Caribbean last September were the highest they have been in a century, said Mark Eakin of the National Oceanic and Atmospheric Administration (NOAA).
Coral reefs in the Caribbean experienced more heat stress in 2005 than the past 20 years combined, said Eakin, who coordinates NOAA's Coral Reef Watch satellite monitoring program.
"This was the most devastating bleaching event that we've seen in the Caribbean," he said.
Jeff Miller, a National Park Service fisheries biologist based at Virgin Islands National Park in St. John, says the bleaching episode is the most extensive he's seen in 21 years of marine studies.
In Panama 70 percent of the corals at monitoring sites showed signs of bleaching, according to NOAA.
In Mexico 40 percent showed bleaching, while in Texas coral bleaching at sample sites ranged from 35 to 100 percent.
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