Environmental Correlates of the Distribution of Planktivorous Fishes in the One Tree Reef Lagoon

Current theories concerning the determinants of community structure in coral reef fishes emphasize the stochastic elements associated with survival, dispersal and recruitment onto the reef of the planktonic larval stage typical of such fishes.To assess the significance of such elements on reef fish distribution, the present study compares the distribution on small patch reefs of several groups of 'normal' planktivorous fishes with that of Acanthochromis polyacanthus (Pomacentridae), a small planktivorous species that is well documented to lack such a planktonic dispersal stage.The comparison, based on repeated visual censuses of 26 reefs, revealed: ( 1 ) the abundance of A. polyacanthus correlated signif~cantly with those of both nocturnal planktivores and diurnally active planktivores other than A. polyacanthus; (2) of 9 environmental variables examined, 3 (current strength, reef depth and abundance of the dominant piscivore Plectropornus leopardus), in one combination or another, dominated correlations with the distribution of all 3 groups, ( 3 ) A. polyacanthus appeared to be no more predictable in its occurrence than the 'normal' species.These results suggest that post-settlement factors alone, such as movement of juveniles and sub-adults and mortality due to piscivore activity, can account for much of the variance in abundance and unpredictability of occurrence characteristic of reef fishes.The distributions of the various planktivores are also discussed with respect to reef size, current strength and levels of piscivore activity.