Carbon and nitrogen stable isotope analyses indicate the influence of land use on allochthonous versus autochthonous trophic pathways for a freshwater Atyid shrimp

Aquatic ecosystem community dynamics are affected by anthropogenic pressures and subsequent environmental change. This study investigated the influence of land use in the Richmond River Catchment (New South Wales, Australia) on dietary sources for the freshwater Atyid shrimp Paratya australiensis. Carbon and nitrogen stable isotopes and Bayesian modelling determined the contribution to shrimp diets of two autochthonous sources (microphytobenthos and macrophytes) and two allochthonous sources (C3 and C4 plants) across sites characterised by five different land uses: forest, macadamia, grazing, sugar cane and urban. It was hypothesised that allochthonous sources would contribute more to shrimp diets at sites with more extensive riparian zones, but this was not substantiated. Autochthonous sources dominated shrimp diets across all land uses, although their dietary contribution varied with land use, likely reflecting changes in riparian and in-stream habitats and source availability. Autochthonous contributions were lowest and allochthonous contributions were highest, for shrimp at grazing and sugar cane sites, despite minimal riparian vegetation. A complex array of interactions may influence diets of in-stream consumers. This micro-catchment scale study demonstrated that land use changes play a key role in affecting carbon and nitrogen sources for P. australiensis and have the potential to change community dynamics in freshwater streams.