ABSTRACT
Understanding the pattern of energy flow between trophic levels is a fundamental goal of ecology. In aquatic ecosystems energy fixed by primary producers is transferred to other trophic levels via the grazing of herbivores, or the detrital pathway (Begon et al. 1990). For coral reef ecosystems, fishes that feed on epilithic algal communities (EACs) are an important component of food webs, providing a major trophic link between primary production by algae and secondary consumers. It is often assumed that turf-forming filamentous algae are the primary source of nutrition for these fishes (Horn 1989, Polunin 1996, Hatcher 1997). However, it is well recognised that the EAC is a complex structure, in which invertebrates, detritus, microbes and microalgae co-occur and all represent potential sources of nutrition (Hatcher 1983, Choat 1991). Consequently, this conglomeration of living and non-living resources may be better referred to as an epilithic algal matrix (EAM) (Wilson & Bellwood 1997). Fishes feeding on the EAM can not necessarily be assigned the trophic status of herbivore, as they may ingest, digest and assimilate dietary items other than algae. The relative importance of the different EAM components to a fish’s diet has important implications for our understanding of coral reef trophodynamics.
