Widespread disease in Caribbean sea fans: II. Patterns of infection and tissue loss

Large lesions and widespread tissue loss in the sea fans Gorgonia ventalina and G. flabellum L. occurred throughout most of the Caribbean during 1995 and 1996. An earlier study identified the putative pathogen as a fungus in the genus Aspergillus (Smith et al. 1996). Repeated surveys showed that in the Bahamas the incidence (= % pf diseased sea fans) and virulence (= % tissue loss per diseased colony) of the disease increased rapidly from 1995 to 1996. Repeated surveys in Curacao and Saba showed Little variation in incidence and virulence. Incidence of the disease was higher on larger than on smaller colonies. On sheltered or moderately exposed shallow reefs (<12 m), both incidence and virulence were positively correlated with water depth. The number of lesions on diseased sea fans, measured only in Curacao, also increased with depth. These patterns may result from a decrease in wave action, which usually declines with water depth, and the consequent reduction in the swaying motion of the sea fans, thus affecting success of pathogen attachment and establishment. The sea fan predator snail Cypohoma gibbosum was more abundant on diseased than on healthy colonies but its density appears to have been too low to contribute significantly to infection and tissue loss. Algal tumors were found on both healthy and diseased colonies and showed no clear association with the disease.