The effects of surface geology and stream size on freshwater mussel (Bivalvia, Unionidae) distribution in southeastern Michigan, U.S.A.

Stream size and surface geology are the two major environmental features thai control the distributions of the thirty‐four species of unionid mussels living in the streams of southeastern Michigan. Surface geology, a previously unrecognized factor in the ecology of freshwater mussels, acts lo regulate the hydrology, slope and turbidity of streams in the study area. Reciprocal averaging ordinations are used to aid the description of the habitats occupied by each mussel species.