Abstract
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, compared with two coastal rocky reef sites. Fish assemblages were surveyed with Baited Remote Underwater Video (BRUVs) and the species abundance, richness and biomass of fish were classified into nine functional feeding groups (6 teleost and 3 elasmobranch). Comparable metrics for coastal fish assemblages were obtained from published surveys using BRUVs. 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% in Botany Bay) or macrophytes (58% in Lake Macquarie). 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%). Trophic pathways which support fish assemblages, are key in identifying mitigation measures which can help conserve these populations with growing urbanisation of estuaries and coasts.
Highlights
Marine ecosystems are supported by primary production (Litchman and Klausmeier 2008; Oczkowski et al 2016), decomposition and the detrital pathway (Moore et al 2004)
More than half of the fish biomass of coastal rocky reefs depends on zooplankton; the trophic basis of estuarine fish assemblages remains unknown
Comparable metrics for coastal fish assemblages were obtained from published surveys using BRUV, remote underwater video and visual census survey methods
Summary
Marine ecosystems are supported by primary production (Litchman and Klausmeier 2008; Oczkowski et al 2016), decomposition and the detrital pathway (Moore et al 2004). This is supported by a recent analysis of a decade of visual census data by citizen scientists (Reef Life Survey; Edgar et al 2020) over 12 degrees of latitude off eastern Australia (Holland et al 2020)
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