Towards a reefscape ecology: relating biomass and trophic structure of fish assemblages to habitat at Davies Reef, Australia

The complex relationship between coral reef fish assemblages and reef habitats at Davies Reef, a middle-shelf reef in the Great Barrier Reef, Australia, was approached from a reefscape perspective. A reefscape merges the spatial patterns found in a reef with 3 ecological components: structure, function and change. The main objective of this study was to explore the relationship between function (biomass and trophic structure of fish assemblages) and structure (reef habitat) within a reef. Three reef fish groups were defined using multi-dimensional scaling, and their similarity was evaluated using SIMPER analysis. From the benthic surveys conducted at the same sites we defined 3 reefscapes: A, 'encrusting non-Acropora', B, 'Acropora' and C, 'low density massive non-Acropora'. Reefscape A was characterised by maximum fish species richness and biomass, while maximum fish diversity was found in Reefscape B. Reefscape C had the minimum values of fish biomass. The relationship between fish groups (using biomass as a proxy) and habitat was explored using redundancy analysis, which was also used to identify significant fish species within each reefscape. The relationship between the trophic structure (guilds) and habitat was explored using the 4th corner analysis, and this analysis revealed that substratum types differed in terms of their utility as proxies for associated fish species and trophic guilds. The present study stresses the importance of within-reef variability as a determinant of composition and relative abundance of local reef fish assemblages. It also suggests that, while loss or change of habitat structure (i.e. coral cover or change in the dominant coral type) could reduce species richness and biomass, some of the habitat features to which fishes cue are probably coarser geomorphological and environmental zones.