Assessing the trophic link between seagrass habitats and piscivorous fishes

Links between piscivorous fishes and seagrass habitat were investigated in Port Phillip Bay, Australia. Abundances of piscivorous fish were estimated, the contribution of fish to their diets was measured and the trophic link between these fish and seagrass beds was assessed with stable isotopes. Piscivorous fishes were common in seagrass and included eight species from seven families (33% by abundance). They consumed at least eight families of teleost prey, including juveniles of seagrass-associated taxa, such as monacanthids (e.g. Meuschenia freycineti) and syngnathids (Stigmatopora argus). No fish were exclusively piscivorous and contribution of fish to the diets of the most common species (Arripis truttacea and Kestratherina esox) varied strongly through time. Putative contributions of each source (primary producer – plant) to the nutrition of piscivorous fishes were: (1) fishes whose base for nutritional support was driven mostly (>50%) by seagrass (e.g. Platycephalus speculator and Platycephalus laevigatus); and (2) fishes whose base for nutritional support was not driven by any particular primary producer (e.g. Arripis truttacea and Pseudocaranx dentex). The propensity for piscivorous fish to include seagrass-associated fish in their diets, their perennial presence in seagrass and the strong putative contribution by seagrass to their nutrition, suggest that seagrass habitats can be valuable habitat for piscivorous fishes.