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Fusconaia masoni (Conrad, 1834)
Atlantic Pigtoe
Federal Protection: Listed Threatened
State Protection: Endangered
Global Rank: G1
State Rank: S1
Element Locations Tracked in Biotics: Yes
SWAP High Priority Species (SGCN): Yes
Element Occurrences (EOs) in Georgia: 7
Habitat Summary for element in Georgia: Medium sized streams to large rivers from the Ogeechee River northward; coarse sand and gravel at downstream edge of riffles; fast flowing and well oxygenated water
Shell profile is sub-rhomboidal and rarely exceeds 50 mm (2 inches) in length. The umbo is positioned slightly anterior of middle of valves and is elevated well above the hingeline. Anterior margin round while posterior margin typically truncate. Posterior ridge is prominent. Periostracum is yellow to dark brown and clothlike. Nacre color typically white. Individuals occurring in headwater streams tend to be more elongate.
None
The preferred habitat for this species is coarse sand and gravel at the downstream end of riffles. This species is rarely found in substrates of fine sand and silt or mud.
The diets of unionids are poorly understood but are believed to consist of algae and/or bacteria. Some studies suggest that diets may change throughout the life of a unionid with juveniles collecting organic materials from the substrate though pedal feeding and then developing the ability to filter feed during adulthood (Vaughn and Hakenkamp 2001).
Gravid individuals have been found during late June. The bluegill (Lepomis macrochirus) and shield darter (Percina peltata) successfully transformed glochidia of this species.
Surveyors should consider sampling during periods when female individuals are spawning or brooding as this species may have higher detection rates during this period. Although no live individuals have been collected in Georgia, it is possible that the species may still persist. The Ogeechee River harbors relatively large populations of native unionids, which may hinder the detection of this species. Continued survey efforts in this basin will help to determine if this species persists in the basin. Survey data for the Brier Creek sub-watershed is lacking, therefore the Atlantic Pigtoe may persist in Brier Creek.
This species historically occurred from the James River basin in Virginia south to the Altamaha River basin of Georgia. In Georgia, this species was historically collected from the type locality and from Mill Race in the Brier Creek sub-basin (Savannah River Basin) in Burke County. Within the Ogeechee River basin, this species was historically collected from the Ogeechee River in Warren and Screven counties, as well as the outfall of Magnolia Springs in Jenkins County, and the Ogeechee River in Screven County. The Atlantic Pigtoe was last collected in Georgia during a 1991 survey of the Ogeechee River Basin. Only four live individuals were collected from Williamson Swamp Creek near Bartow in Jefferson County despite extensive searches throughout the entire basin. In 2004 and 2007, surveys of historical locations yielded no live individuals. Although surveyed extensively in the past, only two historic records of the Atlantic Pigtoe are known from the Altamaha River. and the species is presumably extirpated from the basin.
Currently, the Ogeechee River basin of Georgia is experiencing substantial development and timber removal along the banks. Excess sedimentation due to inadequate riparian buffer zones, development, and agriculture covers suitable habitat and could potentially bury mussels. Poor agricultural practices may also cause eutrophication and degrade water quality.
The Atlantic pigtoe is not known to occur on any state properties in Georgia. Unlike terrestrial species, the occurrence of an aquatic species on state or federal lands may not eliminate habitat degradation due to the influences of upstream and downstream disturbances.
Examination of the basic life history was identified as a top research priority needed for the conservation in the Georgia Wildlife Action Plan. Understanding the basic life history of this species will provide the foundation upon which all other research and conservation actions should be built. In addition, developing environmental DNA (eDNA) methodologies may aide in the location of extant populations of the species in Georgia. Lastly, a thorough survey of the Ogeechee and Brier Creek watersheds are needed to determine if any additional populations may exist .
Alderman, J.M. 1991. Status survey for the Atlantic pigtoe (Fusconaia masoni) in Georgia. North Carolina Wildlife Resources Commission, Raleigh.
Alderman, J.M. 2007. Atlantic pigtoe (Fusconaia masoni) surveys in Georgia. Georgia Department of Natural Resources, Wildlife Resources Division, Nongame Conservation Section, Social Circle. 27 pp.
Bogan, A.E. and J.M. Alderman. 2004. Workbook and key to the freshwater bivalves of South Carolina.
O'Dee, S.H. and G.T. Watters. 2000. New or confirmed host identification for ten freshwater mussels. Pages 77-82 in R.A. Tankersley, D.I. Warmolts, G.T. Watters, B.J. Armitage, P.D. Johnson, and R.S. Butler (eds.). Freshwater Mollusk Symposia Proceedings. Ohio Biological Survey, Columbus. 274 pp.
Vaughn C.C. and C.C. Hakenkamp. 2001. The functional role of burrowing bivalves in freshwater ecosystems. Freshwater Biology 46: 1431-1446.
Watters, G.T. and S.H. O'Dee. 1997. Identification of potential hosts. Triannual Unionid Report 13: 38-39.
Williams, J.D, C.E. Skelton, E.M. Schilling, and G.R. Dinkins. 2005. Inventory of freshwater mussels (Family Unionidae) in the Ogeechee River drainage, Georgia, with emphasis on Fusconaia masoni, Atlantic pigtoe, and other rare taxa. Georgia Department of Natural Resources, Wildlife Resources Division, Nongame Conservation Section. Social Circle.
Jason Wisniewski
2018-03-19