The Black Band Disease of Atlantic Reef Corals.

. Some reef building corals in the western Atlantic are susceptible to an infection known as black band disease that is caused by the cyanophyte (cyanobacterium) Phormidium corallyticum R ützler & S antavy . Field observations on the barrier reef of Belize and on reefs of the Bermuda platform indicate the disease is fairly common in susceptible species. Coral tissue destruction monitored in situ in Belize reveals rapid spreading rates and seasonality of the disease. Laboratory experiments confirm that P. corallyticum is the etiologic agent and we speculate that a toxic exudate is the cause of histolysis observed in coral penetrated by the organism. Coral tissue is further broken down by a rapidly developing disease microcommunity, including bacteria and ciliate protozoans, identified with the aid of light, SEM, and TEM photomicrography. Study of P. coraltyticum in culture away from its host coral reveals several ecological requirements, including dependence for optimal growth on yet unidentified organic substances contained in coral tissue. Healthy corals inoculated with various control organisms ‐ including the gliding bacterium Beggiatoa , a filamentous chlorophyte, and six cyanophytes other than P. corallyticum ‐ did not develop the disease. Gorgonacean corals, too, can be artificially infected with P. corallyticum , but naturally occurring gorgonian bands are composed only of noninfectious cyanophyceans.