Biotic and multi-scale abiotic controls of habitat quality: their effect on coral-reef fishes

The influence of habitat quality on a species' demographics is critical for understanding its ecology and effective conservation. However, quantifying habitat quality is problematic because it may comprise of abiotic components at different spatial scales and also be influenced by biotic processes. This study investigated the relationship between reef-associated Caribbean fishes and habitat quality at 2 spatial scales: (1) multiple characteristics of Montastraea annularis coral colonies (<1 m(2)) and (2) coral density in a 5 x 5 m plot around each microhabitat. Furthermore, the influence on habitat quality of 2 biotic factors (predation pressure and interactions between competitively superior territorial damselfishes and other species) was considered. A total of 102 M. annularis colonies within thirty 25 m(2) plots were surveyed on a Belizean forereef. Generalised linear mixed-effect models demonstrated that both damselfishes and other reef associated species were correlated with colony-scale habitat quality (more abundant on taller, refuge-rich colonies). Adult reef-associated species were also correlated with larger-scale habitat quality, being more abundant on colonies with high densities of other Montastraea colonies within 25 m(2) (probably higher quality home ranges). However, the presence of damselfishes was associated with reduced abundances of other reef-associated species on M. annularis colonies, reflecting the importance of both biotic and abiotic controls of habitat quality. On reefs, coral mortality will reduce the density of optimal colonies and potentially increase the proportion occupied by damselfishes. This may lead to smaller populations of inferior competitors as they are increasingly displaced onto sub-optimal microhabitats.