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Alasmidonta triangulata (I. Lea, 1858)
Southern Elktoe
Federal Protection: No US federal protection
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: 16
Habitat Summary for element in Georgia: Gently sloping banks with soft substrate. Often in slackwater areas and possibly in reservoirs. Mixtures of mud, sand, and gravel substrate
The Southern Elktoe has a moderately thin, inflated shell, often with distinct concentric sculpturing originating at the umbo and rarely exceeding 70 mm (2⅞ inches) in length. Umbos are elevated above the hingeline and positioned to the anterior portion of the sub-triangular shell. Anterior margin of shell is rounded while posterior margin is bluntly pointed. Posterior ridge sharp angular. Adults typically with dark brown to black periostracum with faint rays while young individuals have yellow to green with green rays present. Left valve often with two compressed, poorly developed pseudocardinal teeth and reduced or absent lateral tooth. Right valve with one compressed, high pseudocardinal tooth and lateral teeth reduced or absent. Umbo cavity is deep and nacre white.
Triangle Floater (Alasmidonta undulata) and Altamaha Arcmussel (Alasmidonta arcula). Little conchological difference exists between these species. As a result, these specimens may be best identified using a combination of molecular techniques and biogeography.
Typically occupies large creeks to large rivers with soft substrates of silt, mud, sand, or gravel, often in slackwater and pools.
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).
Brooding individuals were collected in October 2014 but glochidia had poor viability (J. Wisniewski and J. Nelson, unpublished data). Additional life history work initiated in 2017 found females brooding viable glochidia in November.Primary host fishes for the Southern Elktoe appear to be catostomids (P.D. Johnson, personal communication).
Surveyors should consider sampling during periods when female individuals are spawning or brooding as this species may have higher detection rates during this period. Surveys should also focus on reservoirs and small impoundments which may be of importance to the conservation of this species. However, since basic life history information for many of Georgia’s unionids is lacking, sampling during periods when closely related species are spawning or brooding may increase probability of detection.
This species was historically reported from the Savannah, Ogeechee, Flint, and Chattahoochee Rivers in Georgia. However recent genetic analyses suggest that individuals found in the Ogeechee and Savannah rivers are the Altamaha Arcmussel; therefore, the Southern Elktoe is likely restricted to the Flint and Chattahoochee rivers. The Southern Elktoe is currently known only from Chickasawhatchee Creek near Elmodel Wildlife Management Area in Baker County (Golladay and Muenz 2005), Patsiliga Creek in Taylor County, and Flint River near Bainbridge in Decatur County (Wisniewski et al. 2014). An additional weathered shell was also collected from Potato Creek, Upson County (Crow 2000). One population also remains in Uchee Creek (Chattahoochee River), Russell County, Alabama. The largest population of the species appears to occur in the lower Flint River near Bainbridge.
Habitat fragmentation may isolate populations and prevent fish movement, limiting the distribution of host fishes carrying glochidia. Additionally, construction of impoundments may further fragment populations and inundate suitable habitat. Excessive water withdrawals in the lower Flint River basin coupled with severe drought could cause this species to become extirpated from Georgia. Excess sedimentation due to inadequate riparian buffer zones also covers suitable habitat and potentially bury individuals.
The Southern Elktoe is known from Chickasawhatchee Creek in the vicinity of Chickasawhatchee and Elmodel Wildlife Management Areas in Georgia. However, 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.
Continuing survey efforts for the Southern Elktoe throughout its historical range as well as examining its basic life history were identified as high priority management needs for the conservation of this species in the 2015 Georgia State 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. Determining the hydrologic needs of this species was also identified as a high priority research need for thepopulations occurring in the lower Flint and Chattahoochee river basins.
Crow, C. 2000. Protected fish and mussel survey, U.S. 19/S.R. 3 Bridge Over Potato Creek, Thomaston, Upson County, Georgia. Project No. BRN-006-4(32); P.I. #322922. Prepared for Edwards-Pitman Environmental, Inc. Smyrna, Georgia.
Golladay, S. and T. Muenz. 2005. Survey and relocation of Unionids in Chickasawhatchee Creek and Elmodel Wildlife Management Areas, Southwest Georgia. Annual Progress Report to Georgia Department of Natural Resources. 8 pp.
Johnson, R.I. 1970. The Systematics and zoogeography of the Unionidae (Mollusca: Bivalvia) of the Southern Atlantic Slope Region. Bulletin of the Museum of Comparative Zoology 140: 263-449.
Vaughn C.C. and C.C. Hakenkamp. 2001. The functional role of burrowing bivalves in freshwater ecosystems. Freshwater Biology 46: 1431-1446.
Wisniewski, J.M. 2007. Unpublished field notes from 2007. Georgia Department of Natural Resources, Wildlife Resources Division, Nongame Conservation Section, Social Circle.
Wisniewski, J.M., N.M. Rankin, D.A. Weiler, B.A. Strickland, and H.C. Chandler. 2013. Occupancy and detection of benthic macroinvertebrates: a case study of unionids in the lower Flint River, Georgia, USA. Freshwater Science 32:1122-1135.
Wisniewski, J.M., N.M. Rankin, D.A. Weiler, B.A. Strickland, and H.C. Chandler. 2014. Use of occupancy modeling to assess the status and habitat relationships of freshwater mussels in the lower Flint River, Georgia, USA. Walkerana 17:24-40.
Jason Wisniewski
2018-03-20
