Researchers study pre- and post-Katrina corals

October 08, 2009 — Washington, D.C. — Mass coral bleaching has devastated coral colonies around the world for almost three decades. Now scientists have found that bleaching can make corals more susceptible to disease and, in turn, coral disease can exacerbate the negative effects of bleaching. A paper in the October issue of the journal Ecology shows that when they occur together, this combination of afflictions causes greater harm to corals than either does on its own. 'Traditionally, scientists have attributed coral declines after mass bleaching events to the bleaching alone,' says Marilyn Brandt, a post-doctoral researcher at the University of Miami's Rosenstiel School of Marine and Atmospheric Science and the lead author on the paper. 'This study shows that the interplay between diseases and bleaching can play a much larger role than we realized. Corals rely on algae that live inside each coral polyp to provide nutrients and supplemental oxygen. Bleaching occurs when these colorful algae die out or leave the polyps, often in response to overly warm ocean conditions.