Density and Ecomorphology of a Freshwater Mussel (Elliptio complanata, Bivalvia:Unionidae) in a Rhode Island Lake

Densities of freshwater mussel species in a small (430 ha), shallow (zmax=1.8 m) lake in Rhode Island were determined by a SCUBA survey. The three dominant mussel species included Elliptio complanata (x̄=25.7/m2 ± 12.6 SD), Lampsilis radiata (1.1 ± 0.9) and Ligumia nasuta (0.5 ± 0.6). Anodonta cataracta was found rarely in shallow, sandy areas. A morphological analysis of E. complanata showed that individuals living in silt substratum were larger, older, and narrower relative to those in sand. Growth rates, calculated using data on size (length, height, and width of shell) and age (determined by thin section), showed faster growth in the silt substratum. These results conflict with other ecomorphological analyses of E. complanata and other unionid species. The sand habitat may be worse and/or the silt habitat better for mussel growth, relative to similar contrasts made previously.