The yellow mark of death in corals.

Coral reefs around the world are in serious trouble from pollution, overfishing, climate change, and more. The last thing they need is an infection. But that's exactly what yellow band disease (YBD) is--a bacterial infection that sickens coral colonies. Researchers at the Woods Hole Oceanographic Institution (WHOI) and colleagues have identified the bacteria responsible for the disease and say that YBD seems to be getting worse with global warming.

Just as a doctor can diagnose chicken pox by the small, round bumps on skin, scientists can spot the characteristic markings of YBD. The affliction etches a swath of pale yellow or white lesions along the surface of an infected coral colony. The discolored band is a mark of death. It indicates where the bacterial infection has killed the corals' photosynthetic symbionts, called zooxanthellae, which provide their major source of energy. The coral host suffers from cellular damage, starves, and usually does not recover.

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In the November 2008 issue of the Journal of Applied Microbiology, lead author James Cervino, a guest investigator in the WHOI Marine Chemistry and Geochemistry Department, and colleagues reported that they have isolated the microbes that cause YBD: a group of four new species of vibrio, which combine with existing vibrio on the coral to attack the zooxanthellae. This is the first demonstration that the same microbial culprits are to blame for the disease throughout the Caribbean, as well as halfway around the world in Indonesia, Thailand, and the Philippines.

Cervino and colleagues grew vibrio pathogens together with healthy coral. "Contrary to what many experts have assumed, this disease occurs independently of warming temperatures," he said. But when water temperatures rise, infections become more lethal. "Thermal stress and pathogenic stress are a double-whammy for the organism." With ocean temperatures on the rise and the vibrio pathogens living in tropical oceans throughout the globe, the prognosis for the spread of YBD is rather grim, he said.

Cervino is a professor at Pace University in New York and a visiting scientist at WHOI, working with WHOI geochemist Konrad Hughen. "You have biology and chemistry merging together in this lab at WHOI, and it's turning out to be an amazing collaboration," Cervino said.