> Introduction
Georgia Atlantic Drainages

Georgia is the largest state east of the Mississippi River, spanning five USEPA ecoregions and dissected by rivers draining into the Tennessee, the Mobile Basin, Gulf Florida, and the Atlantic Ocean.  It is perhaps not surprising that the freshwater gastropod fauna of the state is so poorly known.  Although some of the major rivers in the western half of the state have received adequate attention (e.g., Clench & Turner 1956), all the freshwater gastropod surveys conducted in Georgia Atlantic drainages have been limited and local, prior to the present report.

Previous workers in eastern or central Georgia have focused almost entirely on selected prosobranch families - the Viviparidae (Call 1894, Goodrich 1942a, Clench 1962), the Pleuroceridae (Goodrich 1942b, Mihalcik & Thompson 2002), or the Hydrobiidae (Thompson 1969, 1977, Watson 2000).  Goodrich (1939) reported the results of a general survey conducted by Henry van der Schalie on the Ogeechee River, listing Valvata bicarinata, Ferrissia rivularis, Goniobasis catenaria, and various species in the genera Campeloma, Amnicola, Somatogyrus, Physa, and Helisoma.  Thompson & Hershler (1991), although focusing primarily on the hydrobiids, offered some general observations on the biogeography of the entire freshwater gastropod fauna of Georgia.  They described an area virtually "devoid of freshwater snails" in the Suwannee, St. Marys, and Satilla Rivers of the state's southern quarter.  More recently, Sukkestad et al. (2006) have reported seven freshwater gastropod taxa inhabiting the Fort Stewart Army Installation of northern coastal Georgia - Valvata bicarinata, Campeloma decisum, Marstonia halcyon, Goniobasis catenaria, Physa acuta, Helisoma trivolvis, Laevapex fuscus, and Ferrissia sp.

In the ecological literature, populations of both Goniobasis catenaria and "Ferrissia sp" (probably rivularis) were involved in a study published by Nelson & Scott (1962) on food web dynamics in the Middle Oconee River.  Krieger and Burbanck (1976) described microhabitat distribution and movement patterns of Goniobasis catenaria ("suturalis") inhabiting the Yellow River, a tributary of the Ocmulgee. They related environmental features to G. catenaria distribution for purposes of identifying factors limiting local variation in abundance.


> Methods

The database here analyzed includes 845 records from four sources. The largest fraction (413 records) is from the Florida Museum of Natural History in Gainesville.  We queried the FLMNH database to extract freshwater gastropod records from the 86 Georgia counties draining into the Atlantic, deleted brackish-water records, and inspected the remainder to eliminate any Gulf drainage records from counties on the margins.  We also deleted records collected prior to 1955 or those with no date, as well as duplicate records (usually differing only by date).  We then traveled to Gainesville to verify identifications and examine problematic lots.

A total of 66 records are from the Georgia Museum of Natural History in Athens, and 44 records are from the North Carolina State Museum in Raleigh.  Both these data sets were gathered directly from examinations of catalogued lots on site.  The remainder of 322 records is from our own original collections, made 2003-06 using simple untimed searches.

Our final total of 264 sample sites were located throughout the Atlantic drainages of the state, in all ecoregions, all drainages, and all counties. A map (in PDF format) showing the distribution of sites is available as Figure 1.  No “absence stations” are shown.  If freshwater gastropods were not collected at a site, then no record resulted.  Our entire 845 record database is available (as an excel spreadsheet) from the senior author upon request.

> Acknowledgements

We thank John Robinson and Tom Smith for their help with the field work.  Gracious hosts included Mr. John Slapcinsky and Dr. Fred Thompson at the Florida Museum of Natural History, Ms. Liz McGhee at the Georgia Museum of Natural History, and Ms. Jamie Smith and Dr. Art Bogan at the North Carolina State Museum. The success of this project has in large part depended on the GIS and data analysis skills of Dr. Doug Florian, and the webmastery of Mr. Steve Bleezarde. 

> References

Call, R.E. 1894. On the geographic and hypsometric distribution of North American Viviparidae. Amer. J. Science 48:132-140.   Clench, W.J. & R.D. Turner. 1956. Freshwater mollusks of Alabama, Georgia, and Florida from the Escambia to the Suwannee River. Bull. Fl. State Mus., Biol. Sci. 1:95-239.   Clench, W.J. 1962. A catalogue of the Viviparidae of North America with notes on the distribution of Viviparus georgianus Lea. Occas. Pprs. Mollusks 2:261-285.   Goodrich, C. 1939. Certain mollusks of the Ogeechee River, Georgia. Nautilus 52:129-131.   Goodrich, C. 1942a. The American species of Viviparus. Nautilus 55:82-92.   Goodrich, C. 1942b. The Pleuroceridae of the Atlantic Coastal Plain. Occas. Pprs. Mus. Zool. Univ. Mich. 456:1-6.   Krieger, K.A. & W.D. Burbanck. 1976. Distribution and dispersal mechanisms of Oxytrema (= Goniobasis) suturalis Haldeman (Gastropoda: Pleuroceridae) in the Yellow River, Georgia, U.S.A. Amer. Midl. Natur. 95:49-63.   Mihalcik, E. L. & F. G. Thompson 2002.  A taxonomic revision of the freshwater snails referred to as Elimia curvicostata, and related species.  Walkerana 13: 1 - 108.   Nelson, D.J. & D.C. Scott. 1962. Role of detritus in the productivity of a rock-outcrop community in a piedmont stream. Limnol. Oceanog. 7:396-413.   Sukkestad, K.E., E.P. Keferl, E.P. & T.D. Bryce. 2006. Freshwater mollusks of Fort Stewart, Georgia, U.S.A. Amer. Malac. Bull. 21:31-38.  Thompson, F.G. 1969. Some hydrobiid snails from Georgia and Florida. Quarterly J. Fl. Acad. Sci. 32:241-265.   Thompson, F.G. 1977. The hydrobiid snail genus Marstonia. Bull. Fl. State Mus. 21:113-158.   Thompson, F.G. & R.H. Hershler. 1991. Two new hydrobiid snails (Amnicolinae) from Florida and Georgia, with a discussion of the biogeography of freshwater gastropods of South Georgia streams. Malac. Rev. 24:55-72.   Watson, C.  2000.  Results of a survey for selected Hydrobiidae (Gastropoda) in Georgia and Florida.  Proc. First Freshwat. Moll. Conserv. Soc. Sympos. 233 - 244.