BLEACHING OF THE CORAL OCULINA-PATAGONICA BY VIBRIO AK-1

Bleaching in stony corals is the result of a disruption of the symbios is between the coral hosts and photosynthetic microalgal endosymbionts (zooxanthellae). Coral bleaching may be induced by a variety of envir onmental stimuli, including increased seawater temperature. Large-scal e bleaching episodes have been suggested to be linked to global warmin g. We have discovered that coral bleaching, in this case, bleaching of the Mediterranean coral Oculina patagonica, is caused by a bacterid i nfection and that water temperature is a contributing factor. The caus ative agent, Vibrio AK-1, was present in 28 bleached O. patagonica exa mined, but absent from 24 healthy (unbleached) corals. The Vibrio sp. was isolated in pure culture, characterized microbiologically, and sho wn to cause bleaching when inoculated onto unbleached corals. An incre ase in seawater temperature may influence the outcome of bacterial inf ection by lowering the resistance of the coral to infection and/or inc reasing the virulence of the bacterium. When inoculated with 10(6) Vib rio AK-1 ml(-1) at 26 degrees C, bleaching began at around 10 d and af fected more than 80% of the corals after 44 d. Bleaching did not occur under the same conditions in the presence of antibiotics or if the te mperature was lowered to 16 degrees C.