Temporal variation in the structure of reef slope fish communities (central Great Barrier Reef): short-term effects of Acanthaster planci infestation

Temporal and spatial variation in the abundance of acanthurids, caesionids, chaetodontids, labrids, pomacentrids, scarids and siganids was examined on reefs of the central Great Barrier Reef over 4 yr. The reef slopes of 3 outer shelf reefs, 4 mid-shelf reefs and 2 nearshore reefs were first surveyed by visual censuses in 1980. In early 1983 large numbers of the coral-feeding starfish Acanthasterplanci appeared at the base of the slopes of 3 of the mid-shelf reefs. By early 1984 live coral cover on the shallow slopes of these 3 reefs had been reduced by 55 to 90 %. The fish communities on each of the reefs were re-surveyed in 1983 and 1984. In 1980, differences in composition of fish communities at similar cross-shelf locations (measured by percentage of species examined that differed significantly in abundance between reefs) ranged from 2 to 29 % (mean = 15 %). Differences between reefs at different locations ranged from 46 to 82 % (mean = 69 %). Temporal changes in the composition of communities within reefs between 1980 and 1983 ranged from 0 to 5 % (mean = 3 %) on those reefs unaffected by A. planci and from 7 to 15 % (mean = 10 %) on the affected reefs. Changes in the abundances of scleractinian-feeding chaetodontids, but not of other species, could be readily attributed to changes in the reefs caused by A. planci.