TRENDS IN COMMUNITY STRUCTURE ON A JAMAICAN REEF

A quantitative survey of species composition and diversity along depth gradients at Discovery Bay, Jamaica, in 1992 indicated that coral cover was less than or equal to 5% at all depths, except at 30 m, where it attained 27%. Percent cover by macroalgae ranged from 44 to 79% over the entire reef, with highest values between 5 and 20 m on the fore reef. Coral diversity increased with depth between a low at reef crest to a maximum of 0.96 (Brillouin's index, H) at 30 m. Total species diversity was highest at the back reef site (2.32). Coral cover at shallow depths (1, 5, and 15 m) was an order of magnitude lower than in 1982. Such striking changes in community structure over the past decade indicate how physical and biological perturbations (e.g. hurricanes, reduced urchin populations and fish grazing) have affected the reef.