Unionid mussels often occur as multispecies aggregates called mussel beds and in dense patches within the mussel beds themselves. Thus, their distributions are patchy at 2 spatial scales. We examined the association between mussel assemblage structure and macroinvertebrate assemblage structure at these 2 spatial scales in rivers of the Ouachita Highlands, Arkansas and Oklahoma, USA. We used multivariate variation partitioning techniques to relate variation in benthic macroinvertebrate distribution and abundance to variation in mussel assemblages, environmental variables, spatial variables, and overlapping or shared variation between these components. At the patch scale, total densities of macroinvertebrates and dominant groups (Oligochaeta, Chironomidae, Ephemeroptera, and Trichoptera) were significantly higher in patches containing mussels than where mussels were absent, and densities of macroinvertebrates were positively correlated with unionid density. In variation partitioning analyses, mussel assemblages explained almost ½ of the variation in macroinvertebrate assemblages at both spatial scales, even after removing effects of similar habitat (environmental variables) and biogeographic history (spatial variables).