Trophic Structure of Temperate Australian Oyster Reefs Within the Estuarine Seascape: a Stable Isotope Analysis

Remnant oyster reefs support diverse communities of invertebrates and fish, and there is growing interest in restoring this important habitat. Whether the construction of new oyster reefs will enhance or simply redistribute existing fisheries' productivity depends on their trophic role-which, to date, is unknown for Australian estuaries. In this study, conducted in Port Stephens, Australia, stable isotope analysis was used to determine trophic linkages among remnant oyster reefs and their resident and transient species. Specifically, this study elucidated whether the potential trophic linkages could be arising through the direct consumption of reef-forming bivalves or from the uptake of oyster-generated organic matter found in the sediment and consumption of reef-dwelling organisms. A total of six primary producers and 35 consumers of distinct feeding guilds were sampled. Results indicated oyster reefs are contributing to the trophic ecology of both resident and transient species, both through direct predation on the reef bivalves but also indirectly through consumption of the reef benthic organic matter and consumption of other reef-dwelling organisms. Oysters and mussels were an important prey group (> 40% contribution) for three resident and five transient species, including polychaetes, blue swimmer crabs, toadfish, luderick, leatherjackets, oyster gobies, and stingarees. Benthic organic matter from the oyster reef was found to be a primary resource for 12 residents and four transient species, including crabs, shrimps, gastropods, and fish. Oyster reefs are key foraging grounds in the estuarine seascape, and their restoration will enhance fisheries productivity by broadening the trophic resource base and contribute to the estuarine energy transfer to higher trophic levels.