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Alasmidonta arcula (I. Lea, 1838)
Altamaha Arcmussel
Federal Protection: No US federal protection
State Protection: Threatened
Global Rank: G2
State Rank: S2
Element Locations Tracked in Biotics: Yes
SWAP 2015 Species of Greatest Conservation Need (SGCN): Yes
SWAP 2025 Species of Greatest Conservation Need (SGCN): Yes
2025 SGCN Priority Tier: Highest Conservation Concern
Element Occurrences (EOs) in Georgia: 21
Habitat Summary for element in Georgia: Large Rivers and reservoirs on gently sloping banks with soft and fine sediments. Often under overhanging willlows
Shell is delicate, inflated, often with distinct concentric sculpturing near the umbo. Rarely exceeds 80 mm (3⅛ inches) in length. Umbos are elevated above the hingeline and positioned centrally to slightly anterior of the triangulate shell. Adults typically have brown to yellow periostracum with dark rays. Posterior ridge is sharp and straight. Right valve has one delicate pseudocardinal tooth and a short, delicate lateral tooth. Left valve has one to two delicate, serrated pseudocardinal teeth with lateral teeth absent or reduced. Beak cavity is shallow and nacre is typically white or iridescent.
The Southern Elktoe Alasmidonta triangulata is similar in appearance but these species are allopatric with the Altamaha Arcmussel
Typically found in sloughs, oxbows, or depositional areas in large creeks to large rivers and reservoirs with silt, mud, and/or sand substrates. The Altamaha Arcmussel is associated with a wide range of substrates from coarse sand to medium silt, but this species was most commonly found in fine sand. In 2007, surveys of the Altamaha River found individuals most frequently occupying areas with gently sloping banks, often times with low hanging willows and soft mud. Individuals were less frequently encountered in other habitats, but were sometimes found in coarse sand and gravel substrates in pools of 2 - 3 meters (6 - 9 feet) deep.
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).
Little is known about the life history of the Altamaha Arcmussel. Several animals with partially filled gills have been observed in late May and October. The host fish for the Altamaha Arcmussel is unknown although glochidia have successfully transformed on the Eastern Mosquitofish, Robust Redhorse, and Striped Jumprock. However, the Eastern Mosquitofish is not considered to be a primary host as it is unlikely that these species would interact under natural conditions and metamorphosis success of the Robust Redhorse and Striped Jumprock were low (Johnson et al. 2012).
Surveyors should consider sampling during periods when female individuals are spawning or brooding as this species may have high detection rates during this period. This species is likely to be found in soft substrates along gently sloping banks with low hanging willows.
Historically believed to be endemic to the Lower Altamaha River basin including the Ohoopee, Oconee, Ocmulgee, and Little Ocmulgee rivers. One relict shell was collected in 1993 from Turkey Creek (Oconee River), Laurens County. Recent collections of the species indicated that the species occurs upstream into Lake Jackson (Jasper County) and the Alcovy River in the Ocmulgee River watershed and upstream to Mt. Vernon in the Oconee River. In addition, recent genetic and conchological analyses of specimens collected from the Ogeechee and Savannah river basins suggest that the Altamaha Arcmussel also occurs in these basins. Live individuals have been found at multiple sites in the Savannah River upstream into Clarks Hill Lake.
Excess sedimentation due to inadequate riparian buffer zones covers suitable habitat and could potentially bury mussels. Direct and indirect competition by the introduced Flathead and Blue catfish may be reducing native mussel populations through direct consumption of mussels and their host fishes. All-terrain vehicles may also impact this species within the Ohoopee River (Stringfellow and Gagnon 2001).
| Threat 1 | Threat 2 | Threat 3 | |
|---|---|---|---|
| General Threat | Pollution | Natural system modifications | Pollution |
| Specific Threat | Agricultural & forestry effluents | Dams & water management/use | None |
The Altamaha Arcmussel is known from the Altamaha, Ogeechee, and Savannah river basins. These rivers border several state owned lands in Georgia. These lands are Moody Forest Natural Area, Griffin Ridge Wildlife Management Area (WMA), Big Hammock WMA, Bullard Creek WMA, Horse Creek WMA, Flat Tub WMA, and Tuckahoe WMA. In addition, the Altamaha Arcmussel occurs within several of Georgia Power's project areas included in the Altamaha Candidate Conservation Agreement. 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.
The Altamaha Arcmussels was recommended for removal from Georgia's state protected species list as threats to this species do not appear as eminent as previously thought due to expansions in it known distribution. Examination of the basic life history and development of culture and propagation techniques were identified as a top research priorities needed for the conservation of this species in the Georgia State Wildlife Action Plan. Riparian buffers should be protected to avoid unnecessary bank erosion as this species often is found in shallow areas near the water’s edge.
Clarke, A.H. 1981. The Tribe Alasmidontini (Unionidae: Anodontinae), Part I: Pegias, Alasmidonta, and Arcidens. Smithsonian Contributions to Zoology No. 326. iii+75 pp.
Dinkins, G.R., J.E. Dinkins, and J.E. Daniel. 2004. Survey for native mussels with a focus on Altamaha spinymussel (Elliptio spinosa) and Altamaha Arcmussel (Alasmidonta arcula) in approximately 15 km of Lower Ocmulgee River, Coffee/Telfair/Jeff Davis Counties, Georgia. Final report submitted to The Nature Conservancy, June 2004.
Johnson, J.A., J.M. Wisniewski, A.K. Fritts, and R.B. Bringolf. 2012. Host identification and glochidia morphology of freshwater mussels from the Altamaha River Basin. Southeastern Naturalist 11:733-746.
Keferl, E. P. 1981. A survey of the naiads of the Ohoopee River, Georgia. The Bulletin of the American Malacological Union, Inc., 1981. 11-15.
Keferl, E. P. 1993. The status of freshwater mussels in some Georgia, South Carolina and North Carolina waters, in K.J. Hatcher (ed.), Proceedings of the Georgia Water Resources Conference. Institute of Ecology, The University of Georgia, Athens.
Sickel, James B. 1980. Correlation of Unionid mussels with bottom sediment composition in the Altamaha River, Georgia. The Bulletin of the American Malacological Union, Inc. 10-13.
Stringfellow, C., and P. Gagnon. 2001. Final report of the Altamaha spiny mussel survey in the lower Ohoopee River. U.S. Fish and Wildlife Service. 10 pp.
Vaughn C.C. and C.C. Hakenkamp. 2001. The functional role of burrowing bivalves in freshwater ecosystems. Freshwater Biology 46:1431-1446.
Williams, J.D., C.E. Skelton, E.M. Schilling, and G.R. Dinkins. 2004. 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, Social Circle.
Wisniewski, J.M., G. Krakow, and B. Albanese. 2005. Current status of endemic mussels in the Lower Ocmulgee and Altamaha Rivers, in K.J. Hatcher (ed.), Proceedings of the Georgia Water Resources Conference. Institute of Ecology, University of Georgia, Athens.
Jason Wisniewski
2018-03-16
