boosted chemist
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Here is the link, doubt u guys can see it so here it is
http://www.sciencemag.org/cgi/content/full/329/5995/1001
http://www.sciencemag.org/cgi/content/full/329/5995/1001
Marine Ecology:
Hard Summer for Corals Kindles Fears for Survival of Reefs
Dennis Normile
Coral reefs are reeling from extensive bleaching in the Indian Ocean and throughout Southeast Asia. "It rivals 1998," when massive bleaching associated with high ocean temperatures destroyed 16% of the world's coral reefs, says Clive Wilkinson, a coral reef ecologist at Australia's Reef and Rainforest Research Centre in Townsville. And although some hard-hit areas have cooled"”offering hope that some reefs may rebound"”other regions are just now heating up. Based on current sea surface temperatures, the U.S. National Oceanic and Atmospheric Administration (NOAA) has issued an alert for the Western Pacific and the Caribbean. "We're looking at the potential for very warm temperatures causing significant coral bleaching over the next couple of months," says C. Mark Eakin, a NOAA coral reef ecologist in charge of the agency's Coral Reef Watch.
The blight is expected to harm a host of sea creatures. When the "rainforests of the oceans" are degraded or die, a wide variety of marine life that depend on reefs suffer. And humans too feel the pain: Any decrease in fisheries productivity and loss of tourism affects coastal communities.
Many reefs will be hard pressed to recover from this year's bleaching. According to Eakin, global warming appears to be increasing the frequency of bleaching events. That can spell doom for reefs. "If you get too many repetitive lethal events, the corals will not recover," Wilkinson says.
Corals harbor symbiotic algae called zooxanthellae that use photosynthesis to produce nutrients for themselves and their hosts. Sustained above-average water temperatures and intense sunlight can upset the delicate symbiotic balance, prompting corals to expel zooxanthellae. The corals turn white, or bleach. If weather conditions ease quickly enough, the algae repopulate coral. Prolonged bleaching is lethal.
The most recent massive worldwide bleaching incident occurred in 1998, when El Niño conditions in the South Pacific caused sea surface temperatures to soar across the globe. This year, too, the hand of El Niño was at work. According to Coral Reef Watch, warming started in early summer in the Indian Ocean and persisted until cooling monsoon rains arrived. High temperatures later hit Southeast Asia and the Coral Triangle, which stretches from central Indonesia east to the Solomon Islands and north through the Philippines. In recent weeks, sea surface temperatures have risen in the Western Pacific in a band from Micronesia to Guam and the Northern Mariana Islands, and in the southern Caribbean. In some areas, says Eakin, temperatures "are worse than in '98."
Scientists are still surveying the damage. Early data are grim. Reefs on both sides of the Thai Peninsula were hit, with up to 100% of some coral species bleached, says James True, a coral biologist at Prince of Songkla University in Hat Yai, Thailand. He expects at least 80% of the most sensitive species to die. "A few inshore reefs got so badly damaged they probably won't ever come back to the way they were," he says. Among surviving corals, "disease is rampant," True says, with two to three times the usual incidence of necrotic lesions and growth anomalies. Similar reports of "quite extensive bleaching" have come from Vietnam and through the heart of the Coral Triangle in Indonesia and the Philippines, says Wilkinson, who coordinates the Global Coral Reef Monitoring Network, which tracks reef status and promotes conservation.
Figure 1
Whiter shade of pale. A bleached coral on a Thai reef will likely crumble and litter the sea floor.
CREDIT: JAMES GUEST
[Larger version of this image]
Some ailing reefs had just begun to recover from the 1998 bleaching. "We've got examples of reefs that were bouncing back quite rapidly 10 years after a 90% die off," Wilkinson says. But they were still at least a decade away from full health, and it would take decades longer for slower growing corals to recover. Eakin says that is a particular worry in the Caribbean, where localized bleaching caused extensive coral death 5 years ago and reefs have yet to bounce back.
This year's bleaching event has some disturbing new wrinkles. In some regions, it seems to be hammering normally resistant species while sparing Acropora, a fast-growing coral that is usually the first to succumb. "We don't know why, but it's tempting to suggest it is adaptation," says James Guest, a marine biologist at the National University of Singapore. Acropora that survived in 1998 and repopulated reefs may have had some resistance to bleaching, he says, or perhaps they have taken in zooxanthellae that are less sensitive to higher temperatures. Even if further studies demonstrate some degree of adaptation among corals, Guest warns that future reefs will look quite different from those of today.
Researchers can only watch as the nightmare unfolds. While bleaching is occurring, "there's literally nothing you can do," Wilkinson says. Reefs that were recovering from the 1998 event were far from inhabited coasts or managed in a way to minimize stress from damaging fishing practices and sedimentation from runoff. This year, much of the bleaching is occurring on reefs already under siege.
The long-term prognosis is bleak. Global warming is pushing baseline sea temperatures upward, says Eakin, causing localized bleaching even in years without an El Niño. "Unless there is concerted action to reduce greenhouse gases," he warns, "bleaching will become increasingly common and not just during extraordinary weather events."
