From the Headwaters to the Mouth of the Hatchie River: Freshwater Mussel Distribution and Abundance

Freshwater mussel shells hold great potential to be proxies of past environments; however a clear understanding of the environments they inhabit and their ecological limitations must be known in order to use fossil or archeological shells to interpret past environments. Mussels of the Hatchie River, in western Tennessee, were sampled ca. every 0.5 miles from the river's headwaters to near its mouth over 185 miles for a total of 387 sites. 5,008 individual unionid mussels from 28 species were recorded at 314 sites, or 24.3 (± 1.79 s.e.) mussels per person/hour. Both species richness and abundance increased from the headwaters downstream to within 30 miles of the river's mouth and then decreased. Species richness and abundance were higher in the Mississippi Alluvial Plain and lower upstream where the river flows from the Southeastern Plains ecoregion through the Claiborne and Wilcox Formation, Porters Creek Clay Formation, and McNairy Sand (part of the Cretaceous Ripley Formation). Mussel species richness and abundance were inversely related to mean watershed slope (F= 5.62; df= 1, 11; P< 0.05 and F=6.29; df=1,11; P<0.05, respectively). Asian Clam (Corbicula fluminea) abundance was higher in the upstream Southeastern Plains than the Mississippi Alluvial Plain ecoregion, and its abundance was inversely related to unionid species richness and abundance (F=19.8; df=1,35; P<0.01 and F=34.5; df=1,35; P<0.01, respectively). No mussel age or growth data were collected, but sclerochronological analyses would help elucidate growth rate differences, if any, through out the ranges of single species. These analyses could also determine the environmental conditions necessary for growth as well as changes in past conditions.