The natural history and morphology of blue mud shrimp, Upogebia pugettensis, burrows indicate that they farm their burrow linings. We tested the farming hypothesis by comparing carbon and nitrogen isotope, Carbon-13 and Nitrogen-15 ratios in tissues of U. pugettensis, their commensal clams, Naearomya rugifera and Cryptomya californica, and their isopod parasite, Orthione griffenis with other species and trophic groups co-occurring in the same mudflat, including the burrowing ghost shrimp Neotrypaea californiensis and Neotrypaea gigas, benthic clams and polychaetes. Ratios of these isotopes can indicate the relative trophic positions of organisms. We found similar isotope ratios among U. pugettensis and their commensal clams and that were different from isotope ratios in other clams and trophic groups occurring outside of the burrows in the same mudflat. The common isotope ratios among U. pugettensis and its commensal clams relative to these isotope ratios in other suspension and deposit feeding species in the same community are consistent with farming of the burrow lining.