Unusually warm ocean water is draining the life--and color--out of the world's coral reefs. Researchers estimate that "bleaching" could kill up to 60% of coral within a few decades. But a new study published in tomorrow's issue of Nature reports that some species may be equipped with a previously unknown coping mechanism that helps them survive bleaching events. The discovery could help scientists better predict how reefs will respond to global warming.
Tiny organisms called coral polyps are responsible for producing much of the limestone foundation of reef communities. They get their nutrients from photosynthetic algae that live with them and bestow the corals with their vibrant colors. But the algae flee when water temperatures rise. Most of the abandoned coral turn bone-white and starve within a few weeks or months. Yet inexplicably, some species manage to recover.
To find out why, Andrea Grottoli, a marine scientist at Ohio State University in Columbus, and her students bleached two species of branching coral in warm water. After several weeks, they returned the samples to the Hawaiian reef where they were collected to see whether they would recover.
Even in its original habitat, Porites compressa struggled to survive. But Montipora capitata bounced back in an unexpected way. Laboratory tests showed that the coral made up for the lack of algae by consuming five times more plankton from the surrounding waters than their healthy counterparts did. "It means there's a potential that there are corals better equipped to deal with bleaching," says Grottoli. Furthermore, she says, because they might be strong enough to reproduce successfully in stressed environments, resilient species like M. capitata could eventually dominate reefs. "It gives us a better idea of how reefs might change," says James Palardy, a study author and an ecology graduate student at Brown University in Providence, Rhode Island.
Previous bleaching studies focused on the role of the algae, not the coral, says Michael Lesser, a coral reef biologist at the University of New Hampshire in Durham. "This is a completely different tack," he says. "It's really fascinating." Now scientists need to determine just how many of the thousands of coral species are capable of using this mechanism, and whether they can build and sustain large communities, says Rich Aronson, a marine biologist at the Dauphin Island Sea Lab on Dauphin Island, Alabama. And although their built-in stopgap measure won't single-handedly save the reefs, he says, "it shows they're not hopelessly bereft of a way of coping."
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