The Trophic Basis of Fish Assemblages in Temperate Estuarine and Coastal Ecosystems

Abstract

\n More than half of the fish biomass of coastal rocky reefs depends on zooplankton; however, the trophic basis of estuarine fish assemblages remains unknown. We quantified the trophic basis (i.e. basal energy sources) of fish community biomass inhabiting three habitat types (seagrass, natural reef and artificial reef) in two estuaries, and at two coastal rocky reef sites. Estuarine fish assemblages were surveyed with Baited Remote Underwater Video (BRUVs). Species abundance, richness and biomass of fish were classified into 9 functional feeding groups (3 elasmobranch and 6 teleost). Comparable metrics for coastal fish assemblages were obtained from published surveys using BRUV, remote underwater video and visual census survey methods. Using the functional feeding group biomass and the group-specific diet composition, the breakdown of energy sources was calculated using a food web analysis. Estuarine reef habitats had different species and different functional feeding group composition than seagrass habitat. The majority of fish biomass in the seagrass habitat was supported by detritus (51% at one estuary) or macrophytes (58% at the other estuary). In contrast, zooplankton supported most fish biomass (45-59%) at the coastal reef locations, and in reef habitat in one estuary (35-43%), but not the other estuary (33-34%). The trophic basis of estuarine and coastal fish assemblages reveals their potential response to urbanisation including changes to habitat, nutrient supply and current flow.