This affliction etches a swath of pale-yellow or white lesions along the surface of an infected coral colony. The discoloured band is a mark of death, indicating where the bacterial infection has killed the coral’s photosynthetic symbionts, called zooxanthellae. The coral host suffers from cellular damage and starves without its major energy source, and usually does not recover.

In a paper published in the November 2008 issue of the Journal of Applied Microbiology, lead author James Cervino and his colleagues report isolating the bacteria that cause YBD: a group of four new Vibrio species, which combine with existing Vibrio on the coral to attack the zooxanthellae.

This is the first demonstration that the same bacterial culprits are to blame for the disease throughout the Caribbean as well as half way around the world in Indonesia.

Worldwide epidemic

The broad distribution of the core group of Vibrio also helps explain the expanding incidence of YBD throughout the world’s tropical oceans, Cervino says.

The Vibrio bacteria that cause Yellow Band Disease are part of a family with a reputation for disease. “What we have are coral pathogens that are genetically close to shellfish pathogens,” Cervino says. For example, one of the Vibrio bacteria found in corals also causes infections in prawns, shrimp, and crabs. The bacteria are also distantly related to Vibrio cholera, the pathogen that causes human cholera epidemics. There is no known danger to humans from YBD, however.