Dietary contributions of the alien zebra mussel Dreissena polymorpha in British freshwater fish suggest low biological resistance to their invasion

Native communities can resist the establishment and invasion of alien species through consumptive and/or competitive interactions. The extent of consumptive resistance from freshwater fish to the invasion of zebra mussels Dreissena polymorpha, a globally invasive Ponto-Caspian species, was assessed in two areas in Britain using stable isotope analysis, where mixing models predicted the contribution of putative prey resources (including zebra mussel) to fish diet. Across the sites and species, only roach Rutilus rutilus were predicted to have a diet where zebra mussels contributed highly (predicted contribution: 44%), with literature suggesting that their functional morphology would have facilitated their consumption of this prey item. Predicted contributions of zebra mussels to common bream Abramis brama diet was comparatively low (29%), despite them being present to much larger sizes than roach, and with pike Esox lucius, perch Perca fluviatilis and pikeperch Sander lucioperca also predicted to have low dietary contributions of zebra mussels (0.08%, 24% and 24%, respectively). These results suggest the consumptive resistance to its invasion in Britain has been low and, correspondingly, if there is a management desire to further limit the invasion of zebra mussels then relying on biological resistance to limit their invasion appears to be insufficient.