Effects of habitat on fish abundance and species composition on temperate rocky reefs

The influence of temperate rocky reef habitat factors on associated fish assemblages is poorly understood. In particular, the effect of depth on fish abundance and species composition is understudied in coastal environments (and the transition zone of macroalgae to non-macroalgae reefs) due to limitations of traditional visual survey methods. This study used a 'drop camera' survey method for 37 reef sites off the coast of Sydney, Australia, between 6 and 57 m depth, to create explanatory models linking relative fish abundance, species richness, and species composition with reef habitat factors. Generalised linear mixed modelling revealed that total fish abundance and species richness increased with small-scale structural complexity and biological cover. Reefs with greater density of surrounding reef substrate also had increased species richness. Although depth did not influence fish abundance or species richness, a multivariate analysis showed that it did influence species composition, with a decline in herbivores and omnivores with depth compensated by a general increase in other groups. The response of species composition to habitat factors was measured using multivariate generalised linear modelling and latent variable modelling. We found a weak response to depth and habitat complexity, but the lack of strong patterns and correlation between fish species shows that reefs within the similar to 300 km(2) of coastline investigated here are difficult to classify based on habitat-driven patterns in their associated fish assemblages. These findings enhance our understanding of temperate rocky reefs, and have relevance for the management of coastal habitats, including habitat zonation and the deployment of coastal artificial reefs.