Habitat–fishery linkages in two major south-eastern Australian estuaries show that the C4 saltmarsh plant Sporobolus virginicus is a significant contributor to fisheries productivity

Abstract

Estuarine fisheries productivity is dependent upon numerous factors, including the productivity of primary producers supporting the food web and the transport of organic matter derived from those primary producers. In this study, we use stable isotope ratios in a Bayesian mixing model to estimate the contribution of primary producers to fully recruited commercial species in two important estuarine commercial fisheries in south-eastern Australia; the Hunter and Clarence estuaries. The C4 saltmarsh plant Sporobolus virginicus had the greatest contribution to consumer diet among almost all sites and times (25–95%), though for prawns the presence of seagrass may be exerting some influence on this calculated contribution in the Clarence estuary. Particulate organic matter (POM; 30%) and fine benthic organic matter (FBOM; 39–41%) also contributed significantly to consumer diet. Mangroves and other C3 sources generally had the lowest contribution to consumers (1–31%). While the exact contributions of each source are uncertain within our Bayesian framework, these results highlight the relatively large role of saltmarsh habitat as a contributor to fishery productivity, especially in estuaries with no seagrasses. Given the anthropogenic threats to saltmarsh habitat, there is potential for loss of fishery productivity with further loss of saltmarsh areal extent.