Will the experimental population control of an invasive crayfish influence the diet and trophic position of a native crayfish? An assessment using stable isotopes

Context Trophic overlap between invasive and native species can cause a competitive displacement of the native. In Australian freshwaters, the invasive crayfish Cherax destructor has proliferated into the ranges of native Euastacus species.Aims To examine trophic overlap between C. destructor and the critically endangered Euastacus dharawalus and determine whether C. destructor population control causes shifts in the diet and trophic position of E. dharawalus.Methods We compared delta C-13 and delta N-15 values of tissue from both species collected from two sites. Population control of C. destructor was then conducted at one site, whereas the C. destructor population remained uncontrolled at the second site. The delta C-13 and delta N-15 values of E. dharawalus were then once again assessed.Key results Both species occupied similar trophic positions and consumed similar proportions of each food resource prior to control efforts. However, we found increases in the contribution of detritus to the diet of E. dharawalus following the removal of C. destructor, whereas no dietary shifts occurred at the uncontrolled site.Conclusions and implications The increase in detrital consumption suggests that control of C. destructor increased the availability of a preferred resource. Further, dietary competition between C. destructor and E. dharawalus is likely and reinforces C. destructor representing a substantial threat to Euastacus crayfish.