Interrelationships between soft corals and reef-associated fishes on inshore-reefs of the Great Barrier Reef

Abstract

The composition of coral reef habitats strongly influences associated fish assemblages. As habitat formers, soft corals constitute a morphologically diverse component of coral reefs, although their importance as fish habitat is largely unquantified. Our study assessed relationships between soft and hard coral habitats and assemblages of reef-associated fishes on inshore reefs of the Whitsunday Islands, focussing on pomacentrids, chaetodontids and pomacanthids. Study sites varied in hard and soft coral cover and were assessed by the level of exposure to previous cyclone damage. The soft coral community was dominated by Sinularia spp. and constituted an average of 11.4% of benthic cover compared to 16% hard coral cover. At fine spatial scales (250 m2), significant positive relationships between soft coral cover and abundance occurred for 2 species of pomacentrids (Amblyglyphidodon curacao and A. leucogaster) as well as total Chaetodontidae and Pomacanthidae. Further, it was clear that some taxa were associated with specific soft corals. For example, A. curacao, Pomacentrus lepidogenys and Chelmon rostratus were observed associating with branching digitate Sinularia, with a more structurally complex soft coral morphology. The combination of high and medium cover of hard and soft corals supported distinct assemblages of fishes and the highest abundances of many species at the scale of sites (1000 m2). Our results indicate that soft corals provide valuable habitat, supporting diverse fish assemblages by contributing to habitat mosaics on coral reefs. These findings suggest that the ecological role of soft corals has been underestimated and therefore holds direct implications for the management of coral reefs.