> Bithynia tentaculata (Linne 1758)

> Habitat & Distribution
Our North American populations of B. tentaculata originated from European snails introduced into the Great Lakes in the 19th century (Mills et al. 1993, Jokinen 1992).  The "faucet snail" now ranges through the entire Great Lakes – St. Lawrence drainage system, from Quebec west to Wisconsin, as well as in the Mohawk and Hudson Rivers (Burch 1989, Jokinen 1992, Haynes et al. 2005).  The population introduced to the Potomac River of Virginia in the 1930s apparently represents the southern limit of its range (Pilsbry 1932).  

Bithynia inhabits a variety of permanent waters, including ponds, lakes, marshes, canals, and rivers, and occurs on a variety of substrates, including gravel, sand, clay, mud, rocks, and macroscopic vegetation (Jokinen 1992, Haynes et al. 2005, Wojdak and Mittelbach 2007).  It thrives in both mesotrophic and eutrophic lakes, and can dominate snail assemblages where nutrient levels are high (Clarke 1979, Harman & Forney 1970, Harman 2000).  Bithynia populations are, however, apparently restricted to waters relatively high in hardness.  New York populations occurred in habitats with a pH range of 6.6-8.4 and with calcium concentration ranges of 5-89 ppm (Jokinen 1992). 


> Ecology & Life history
While retaining the ancestral ability to graze the substrate (Clarke 1981), Bithynia has evolved a "food groove"at the base of its gill that allows it to filter-feed  (Dillon 2000: 100-101).  The relative importance of grazing and filter-feeding to the energy budget of the snail seems to depend on the environmental concentration of suspended particles (Tashiro 1982, Tashiro & Coleman 1982).  Some interesting experiments involving the defensive behaviors displayed by Bithynia in response to leech predation have been published by Bronmark & Malmqvist (1986). 

Life cycles can be completed in less than one year (Pinel-Alloul & Magnin 1971) - exceptionally rapid for populations of freshwater prosobranchs (Dillon 2000: 161-162).  In New York, Jokinen (1992) reported that egg laying can begin in May or June and continue into July, and that some individuals born in spring may breed in the fall of the same year.  Eggs are deposited on hard substrates, with up to 77 eggs contained in each mass.  Individuals appear to live up to 18 months, and possibly as long as 39 months.  Analysis of the productivity data of Mattice (1972) led Dillon (2000: 126 - 135) to suggest that the B. tentaculata population of Oneida Lake (NY) might be R-adapted, displaying a reproductive effort over an order of magnitude greater than predicted from their body size.

> Taxonomy & Systematics
The taxonomy and systematic position of Bithynia tentaculata have been unambiguous and stable for many years.

> Essay
Populations of B. tentaculata inhabiting rivers and lakes of the Upper Midwest serve as intermediate hosts for digenean flukes that have been implicated in massive waterfowl die-offs.  See my essay of 14Nov07, including a photo of Bithynia on the hoof.

>References
Burch, J.B. (1989) North American Freshwater Snails. Malacological Publications, Hamburg, Michigan, USA.  Bronmark C. & Malmqvist B. (1986)   Interactions between the leech Glossiphonia complanata and its gastropod prey.  Oecologia 69: 268 - 276.  Clarke, A.H. (1979) Gastropods as indicators of lake trophic stages. Nautilus 93:138-142.  Clarke, A.H. (1981)  The Freshwater Mollusks of Canada. National Museums of Canada, Ottawa, Ontario, Canada.  Dillon, R.T., Jr. (2000) The Ecology of Freshwater Molluscs. Cambridge University Press, Cambridge, United Kingdom.  Gilbert, E., Vincent, B. & Rosenberry, L. (1986)  Etude experimentale in situ des effets de la densite et de la quantite nourriture chez le gasteropode Bithynia tentaculata (Mollusca: Prosobranchia).  Can. J. Zool. 64: 1696-16700.   Harman, W.N. (2000) Diminishing species richness of mollusks in Oneida Lake, New York State, USA. The Nautilus 114:120-126.  Harman, W. N & J. Forney (1970)  Changes in the molluscan community on Oneida Lake, NY, between 1917 and 1967.  Limnol Oceanog. 15: 454-460.  Haynes, J.M., N.A. Tisch, C.M. Mayer & R.S. Rhyne. (2005) Benthic macroinvertebrate communities in southwestern Lake Ontario following invasion of Dreissena and Echinogammarus: 1983 to 2000.  Journal of the North American Benthological Society 24:148-167.  Jokinen, E.H. (1992) The freshwater snails of New York State. New York State Museum Biological Survey, New York State Museum Bulletin 482.  Mattice, J. S. (1972)  Production of a natural population of Bithynia tentaculata L. (Gastropoda: Mollusca).  Ekologia Polska 20: 525 - 539.  Mills, E.L., J.H. Leach, J.T. Carlton & C.L. Secor. (1993)  Exotic species in the Great Lakes: a history of biotic crises and anthropogenic introductions. Journal of Great Lakes Research 19:1-54.   Pilsbry, H.A. (1932)  Bithynia tentaculata (L.) in the Potomac. The Nautilus 46:69.  Pinel-Alloul, B. & E. Magnin (1971)  Cycle vital et croissance de Bithynia tentaculata L.  du lac St. Louis, pres de Montreal.  Can. J. Zool. 49: 759 - 766.  Stewart, T. W., & R. T. Dillon, Jr.  (2004)  Species composition and geographic distribution of Virginia's freshwater gastropod fauna: A review using historical records.  Am. Malac. Bull. 19: 79-91.  Tashiro, J. (1982) Grazing in Bithynia tentaculata: Age-specific bioenergetic patterns in reproductive partitioning of ingested carbon and nitrogen.  Am. Midl. Natur. 197: 133-150.  Tashiro, J. & S. Coleman (1982) Filter feeding in the freshwater prosobranch snail Bithynia tentaculata: Bioenergetic partitioning of ingested carbon and nitrogen.  Am. Midl. Natur. 197: 114 -132.  Wojdak, J.M. & G.G. Mittelbach (2007)  Consequences of niche overlap for ecosystem functioning: an experimental test with pond grazers. Zool. Univ. Mich., 417: 1-21