Responses of Reef Fish Communities to Large-Scale Habitat Perturbations

Our ability to predict how communities of coral reef fishes will change in response to habitat alteration depends strongly on understanding the functional relationships of component species with live coral and reef structure, together with how these aspects are shaped by wave exposure and various perturbations.  The forereefs of Moorea, French Polynesia have experienced two ecologically significant pulse perturbations since 2007; a 2007-09 island wide-scale COTS outbreak that severely reduced the cover of live coral around the island followed in early 2010 by a cyclone that reduced the structural complexity of the forereef along Moorea’s north shore by removing much of the dead coral.  Prior to these disturbances, the fish assemblages on the forereef demonstrated consistent spatial differences in species composition that were related to differences in the wave energy incident to different localities around the island.  Following the disturbances, fish communities at these localities responded in a consistent fashion independent of the initial species composition.  Fish species strongly associated with living corals declined island-wide and assemblages found along the usually less wave impacted north shore became more similar to those found along the more wave impacted southwestern shore.  Surprisingly, fish species richness remained virtually unchanged and the total biomass of fishes increased.  This counter-intuitive response resulted from the replacement of small, coral dependent species by larger-bodied, coral rubble associated species and an island-wide increase in the abundance and biomass of herbivores.