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Coral Bleaching Caused by Bacterial Infection
Kushmaro, A., Rosenberg, E., Fine, M. and Loya, Y. 1997. Bleaching of the coral Oculina patagonica by Vibrio AK-1. Marine Ecology Progress Series 147: 159-165.

What was done
The authors performed three laboratory experiments using the coral Oculina patagonica and the bacterium Vibrio AK-1 to determine the ability of the bacterium to infect and cause bleaching in the coral.

What was learned
In the first laboratory experiment, bleached and healthy corals were placed together in aquariums at water temperatures of 17 and 25C. Bleaching was not observed in the healthy corals at 17C, while the already bleached corals actually showed some signs of recovery. At 25C all healthy corals exhibited observable bleaching after 20 days.

The second experiment involved the direct placement of the Vibrio bacterium onto healthy corals, which were then placed in aquariums of 25C. After 6-8 days, all corals showed signs of bleaching at the point of inoculation.

In the third experiment, Vibrio bacteria were injected directly into the aquarium water of healthy corals growing at water temperature of 26C. All corals showed bleaching after 10 days, and colony death was observed shortly after 52 days.

Results of the three experiments revealed that "bleaching was not observed (1) without addition of bacteria, (2) when the temperature of the aquaria was maintained at 16C, or (3) in the presence of 100 mg l-1 of kanamycin and 100 mg l-1 of penicillin-G."

What it means
According to the authors, bleaching of the coral Oculina patagonica along the Mediterranean coast "is caused by a bacterial infection," and an increase in the temperature of seawater can influence the outcome of the bacterial infection by "lowering the resistance of the coral to infection and/or increasing the virulence of the bacterium."

Reviewed 1 June 1999