Hot Year Was Killer For Coral
By Joby Warrick
Record sea temperatures triggered the largest mass die-off of tropical corals in modern times last year, destroying in some areas more than 70 percent of the reef-building creatures whose elaborate homes form the backbone of ocean ecosystems, according to a government study to be released today.
The warm weather of 1998--the hottest year in at least six centuries--left a broad swath of dead or damaged tropical corals from the Caribbean to the eastern Pacific, concludes the report by State Department officials and scientists. It suggests a combination of El Nino and global warming is to blame.
"In 1998, coral reefs around the world appear to have suffered the most extensive and severe bleaching and subsequent mortality in the modern record," says the report, to be presented in Hawaii to a federal task force. "These events cannot be accounted for by localized stressors or natural variability alone."
Corals "bleach" or lose pigment when stressed by disease or environmental changes--such as a spike in ocean surface temperatures--and can die if the conditions persist. Scientists have documented a string of "mass bleachings" since the mid-1980s, but last year's outbreak was unprecedented both in severity and geographic scale, the study says.
Although conditions in 1998 were worsened by a severe El Nino, recent trends suggest that the threat to coral reefs will only increase with time, it says. Further losses, the report adds, could have profound consequences for biodiversity, fisheries and tourism.
"At this time, it appears that only . . . global warming could have induced such extensive bleaching simultaneously throughout the disparate reef regions of the world," the report concludes. "Thus the geographic extent, increasing frequency and regional severity of mass bleaching events are likely a consequence of a steadily rising baseline of marine temperatures."
The scale of coral disease and death in 1998 has been noted in several recent reports by international scientific groups, but the State Department study is the most complete documentation of the problem. It is also the most forceful pronouncement by federal officials linking the phenomenon to climate change.
Other scientists, however, say they aren't convinced of a link to global warming, especially because the ocean warming pattern doesn't match climate forecasting models.
Coral reefs are the foundation of one of Earth's most productive and diverse ecosystems, providing food and shelter for at least 1 million species of animals, plants and microbes. Reefs yield a host of benefits for humans, including food, medicines and tourism income.
In recent decades, scientists have documented a worldwide decline in the health of reefs because of coastal pollution and destructive fishing practices. The gradual degradation may have left corals more vulnerable, experts say.
Corals are tiny animals whose immense colonies form the small layer of living tissue on tropical reefs. They secrete a limestone skeleton, which over generations forms the framework of reefs.
Bleaching results from a disruption in the balance between the coral and tiny algae plants that live inside the coral tissue. The algae supply nutrients for the corals while giving the reefs their vibrant colors. But if the water becomes unusually warm--even by a single degree Celsius above the seasonal norm--the corals expel the algae and take on a ghost-like hue.
Bleached corals generally recover with time, but last year's unremitting heat resulted in "devastating mortality," the State Department report says. According to preliminary data, more than 70 percent of corals died off across a wide region of the Indian Ocean, from the coast of Kenya to the Lakshadweep Islands off southern India. The mortality rate topped 75 percent near the Seychelles and more than 80 percent in the Mafia Marine Park off Tanzania.
Bleaching itself was even more widespread, with many areas reporting 100 percent of corals bleached. The phenomenon was observed in at least 60 countries and island nations in the Indian Ocean, Pacific, Red Sea, Persian Gulf and Caribbean, the study says. Only the central Pacific region appears to have been spared.
"Nothing like this has ever been observed before," said Rafe Pomerance, deputy assistant secretary of state for the environment and development, who will present the findings to a meeting of the U.S. Coral Reef Task Force. "Something is going on, and we have to figure out what it is."
Global Reef Damage
Record-high ocean temperatures last year devastated coral reefs, causing widespread "bleaching" and death. Gray areas below show where surface temperatures reached or exceeded the maximum summertime levels for the first six months of 1998.
SOURCE: National Oceanic and Atmospheric Administration
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