Robert Ryan Evans
Robert Ryan Evans, Historical And Contemporary Distributions Of Aquatic Mollusks In The Upper Conasauga River System of Georgia And Tennessee
Faculty Chair: Dr. Mark Schorr (UTC) and Dr. Paul Johnson (Tennessee Aquarium), co-chairs
The Conasauga River, an upper Coosa River tributary, was historically one of the most diverse rivers within the Mobile basin drainage for freshwater mollusks. The Conasauga River historically supported 37 species ofunionids (Bivalvia: Unionidae), 11 species ofprosobranch gastropods (Mollusca: Gastropoda), and 3 species of sphaerid (Bivalvia: Sphaeridae) clams. I collected records from several museums ranging from 1914 to 1990 to chronicle the historical diversity of the Conasauga River system, and conducted a contemporary survey to compare changes in species distributions and richness over the twentieth century. During this study, a total of 203 collections were made in the mainstem of Conasauga River in 1998-1999, ranging from the headwaters downstream to US Highway 76 bridge in Dalton, Georgia. Additionally, all major tributaries to the Conasauga River above US Highway 76 were sampled, in addition to several sites in the Holly Creek and Swamp Creek systems. Overall species richness of unionids decreased from 37 species in 1917 to 27 species in 1998-1999. Additionally, species richness at 4 well-collected historical sampling locations dropped from x = 23.5 in 1917 to x = 7.5 in 1998-1999. By consistently searching various microhabitats, an increase in species richness for gastropods was recorded, with 20 species collected in 1998-1999 versus 11 species in 1914-1919. Six new gastropod species records for the Conasauga River system are recorded, as well as a Pleurocera sp. that may be undescribed. Three species of sphaerid clams were collected in 1998-99, which agrees well with historical species richness values by H. D. Atheam. Overall, mollusk distributions were observed to be fragmented. An extremely small number of individuals were found of many unionid species, and several species of pleurocerid snails were restricted to shoal areas. Specific factors contributing to this overall decline of mollusks in the Conasauga River system were not examined in this study, but general declines in water quality and reduced in-stream habitat quality due to poor land use practices are suspected.