A Study of the Distribution of Freshwater Mussels (Mollusca: Pelecypoda: Unionoida) of the Lake Champlain Drainage in Northwestern New England

Abstract

Lake Champlain occupies a large shallow basin in northeastern North America and drains to the St. Lawrence River. The freshwater mussel fauna of the lake's drainage system includes both Northern Atlantic and Interior Basin species. An analysis of the distribution of the mussel species in the eastern and southern drainage streams of Lake Champlain reveals that fall lines have controlled upstream migration at various stages during the lake's postglacial history. Species composition differs above and below fall lines within drainage streams and varies geographically between drainage streams. Such distribution patterns may be explained by proposed periodic invasions of Lake Champlain by species during specific postglacial lake stages. simple species lists, with little emphasis being placed on details of distribution of species and how the geography and geology of the region have controlled the dispersal of spe- cies recolonizing Lake Champlain during late Pleistocene and early Holocene times. The present study provides a detailed account of the distribution of the freshwater mussels in the eastern Lake Champlain watershed in northwestern New England. Us- ing extant museum records and data gathered during my own field investigations, and available information on the structural and surface geology of the Champlain lowland and western New England, a history of late and postglacial dispersal of mussels into Lake Champlain is developed. The previous literature on Lake Champlain unionoids is very limited. Concerning the New England sector, Adams (1841, 1853) presented brief lists which provided enough information to firmly document the extension of ranges of several Interior Ba- sin species into Lake Champlain. Adams' observations were repeated in subsequent fau- nal lists (e.g., Stimpson, 1851; Johnson, 1915; Johnson, 1980). Gray (1883) gave Lake Champlain drainages in Vermont as the eastern range limit of Lasmigona compressa. Re- cently, Clarke (1981) listed a few records of Alasmidonta undulata from the Lake Cham- plain drainage in Vermont. Similarly, the portion of Lake Champlain in New York has been little studied with respect to unionoid mussels. Lea (1834) first described Symphynota benedictensis ( =Ano- donta grandis) from near Ticonderoga on Lake Champlain. Dekay (1943) later listed a few Lake Champlain records for unionoids, and some time after, Marshall (1895) listed the known distribution of unionoids in Lake Champlain based on New York State Mu- seum records. Finally, Letson (1905) presented a list of New York unionoid mussels that included all known Lake Champlain records. More recently Clarke and Berg (1959) cited the first record of Anodontoides ferussacianus from Lake Champlain, and Smith (1982) provided records for A. ferussacianus and other species in a few of the uppermost Lake Champlain drainage streams. No reports exist of the mussel fauna in the small portion of the Lake Champlain drainage in Canada.