Edmunds,-P.J. Extent and effect of Black Band Disease on a Caribbean reef. CORAL-REEFS. 1991. vol. 10, no. 3, pp. 161-165 The effect of Black Band Disease (BBD) among colonies of Montastrea annularis, M. cavernosa, Diploria strigosa, D. labryinthiformis, Siderastrea siderea and Colpophyllia natans was determined at 7 shallow locations in the Virgin Islands. Between September 1988 and November 1988, 0.2% of 9204 colonies of these species were infected with BBD in 6908 m super(2) of reef at 22 randomly chosen areas. Infected colonies were not clumped suggesting that the disease is not highly infectious between colonies. BBD infection rates in areas surveyed 4 times between August 1988 and September 1989 in Greater Lameshur Bay, St. John, USVI, were significantly lower in winter compared to summer. BBDs were found on 5.5% of the colonies of D. strigosa) in fall 1988, and 7 out of 12 infected colonies lost > 75% of their tissue in 6 months. Low level, chronic BBD infections could convert 3.9% of the living cover of D. strigosa to free space per year, thereby creating substrata for successional processes.