Depth and reef profile: effects on the distribution and abundance of coral reef fishes

The physical and biological structure of coral reef habitats vary in relation to depth and the profile of the reef, from vertical walls to gentle slopes. The differing roles of depth and reef profile on fish distribution and abundance, and the role of habitat structure in explaining these patterns, have received little attention. Here these effects were distinguished by surveying reef fish species and benthic habitat in quadrats on three aspects (shelf, slope and wall) at each of two depths (5 m and 15 m) in Kimbe Bay, Papua New Guinea. Both depth and reef profile accounted for considerable variation in reef fish communities. Species diversity and richness was highest on the shelf profile and lowest on the wall profile at 5 m. Whereas, at 15 m the opposite was true with the wall profile being the most diverse and species rich profile and the shelf being the least. Wall habitats were the most different from the other two profiles in terms of community structure. Depth had a greater influence on fish communities on slope and shelf habitats, with shallow slopes and shelfs similar to one another, and deep slopes and shelfs also similar. Some rare species, such as Chromis delta and Pictichromis paccagnellae, were restricted only to walls. The relative effects of depth and reef profile on benthic habitat structure were similar to the fish communities, with the sponge and encrusting coral dominated wall habitats being the most dissimilar to the other aspects, with clear depth patterns also. There was a significant correlation between the fish communities present and the habitat availability at the depths and on the reef profiles studied. The correlation was best explained by sand, branching coral, encrusting coral, massive coral and rubble. Depth and reef profile had a significant interaction, which suggests that, clearly, both depth and profile are important factors affecting reef fish communities. Although, benthic habitat appears to only partially explain these patterns.