Summary: Reach- and catchment-scale determinants of the
distribution of freshwater mussels (Bivalvia: Unionidae)
in south-eastern Michigan, U.S.A.
S. E. MCRAE,*,
J. D. ALLAN
AND J. B. BURCH
*North Carolina Natural Heritage Program, Raleigh, NC, U.S.A.
School of Natural Resources and Environment, University of Michigan, Ann Arbor, MI, U.S.A.
Mollusk Division, University of Michigan Museum of Zoology, Ann Arbor, MI, U.S.A.
1. We investigated the diversity and distribution of freshwater mussels at 40 sites in an
agricultural catchment, the River Raisin in south-eastern Michigan, to relate mussel
assemblages and individual taxa to reach and catchment-scale variables. Unionids were
surveyed by timed searches in 100-m reaches, and in-stream and riparian habitat were
quantified as well as flow, water chemistry and channel morphology. Land use/cover and
surficial geology were determined for site subcatchments and riparian buffers.
2. Some 21 mussel species were found overall; richness ranged from 0 to 12 living species
per site. From the upper to middle to lower catchment, the number of individuals, number
of species, ShannonWeaver diversity and relative abundance of intolerant unionids all