Habitat complexity and coral reef fish diversity and abundance on Red Sea fringing reefs

Abstract

The influence of several substratum variables, particularly structural complexity and Live coral cover, on coral reef fish species richness and abundance was investigated. By surveying fish species with varying strengths of association with the substratum and at different sampling scales, this study aims to assess the scale-dependence of correlations between substratum characteristics and fish comn~unity parameters. Fish from 5 families (Acanthuridae, Chaetodonhdae, Labridae, Pomacentridae and Scaridae) were counted along transects by visual census. Substratum charactenstics were measured from stereophotographic transects. Three measures of structural complexity were used: (1) an index of surface area, (2) the vanety of different substrata (biological diversity), and (3) numbers of holes (of hfferent sizes). Although the depth of peak specles richness varied between families, overall there was a trend of increasing species richness with increasing depth. Surface index was a poor predictor of overall species richness but was significantly correlated with pomacentrid species richness and abundance on 200 m transects. In contrast, biological diversity of the substratum (H') was highly correlated with overall fish species nchness. Numbers of holes of 3 sizes taken together accounted for 77 O/ O of the variance in overall fish abundance on the 200 m transects. None of the measures of structural complexity were significantly correlated with species nchness or abundance of small, strongly siteattached fish. Live coral cover was not significantly correlated w t h species richness or abundance of fish from any family (except for a weak correlation w ~ t h abundance of obligate corallivorous chaetodontids).