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Elliptoideus sloatianus (I. Lea, 1840)
Purple Bankclimber
Federal Protection: Listed Threatened
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: High Conservation Concern
Element Occurrences (EOs) in Georgia: 22
Habitat Summary for element in Georgia: Medium to large rivers in ACF and Ochlockonee basins; all substrates except bedrock. Species was 20 times more likely to occur in cobble substrates (Wisniewski et al. 2013)
Shell is thick and heavy and quadrate to rectangular in profile with a maximum length of approximately 8.1 inches (205 mm). Posterioventral margins biangulate. Ventral margins typically straight to slightly arcuate. Posterior ridge prominent dorsally, but flattens ventrally. Periostracum of larger, adult individuals dark brown to black with sculpturing present on most of shell with prominent sculpturing on the last two thirds of the shell. Young individuals typically have shiny yellow to light brown periostacum. Umbo typically elevated above hingeline slightly, but often eroded. Left valve with two heavy pseudocardinal teeth and two lateral teeth. Right valve with one pseudocardinal tooth. Umbo cavity typically shallow and nacre color white with a purple hue present outside of the pallial line.
Washboard (Megalonaias nervosa). The Purple Bankclimber can be distinguished from the Washboard by the former having a rectangular outline, more prominent posterior slope, less scalloping along the posterior margin, and purple nacre near the shell margin.
Typically occupies small to large rivers with moderate current. The Purple Bankclimber occurred most frequently in cobble substrates but was rarely detected in bedrock and clay substrates (Wisniewski et al. 2013; Wisniewski et al. 2014). This species infrequently occurs in small streams but has been found in several direct tributaries to the Flint River.
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).
Mature glochidia of the Purple Bankclimber were collected in early February through April. Successful transformation of glochidia occurred in 14 - 21 days on the Eastern Mosquitofish (Gambusia holbrooki), Guppy (Poecilia reticulata), and Blackbanded Darter (Percina nigrofasciata). Additional host investigations found transformation rates exceeded 79% on several sturgeon species including the native Gulf Sturgeon (Acipenser oxyrinchus desotoi). In addition, Blackbanded Darters and Halloween Darters (Percina crypta) served as marginal hosts with approximately 30% transformation (Fritts et al. 2012).
Surveyors should consider sampling during periods when female individuals are spawning or brooding as this species may have higher detection rates during this period. 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. A complete survey of the mainstem Chattahoochee and Ochlockonee rivers is needed to better understand the current distribution and abundance of the species in Georgia.
Historically known from the Apalachicola-Chattahoochee-Flint Rivers basin and Ochlockonee River of Alabama, Florida, and Georgia. Fossil records indicate that the purple bankclimber historically occurred in the Suwannee River in Florida. This species is currently known from the Apalachicola, Flint, Chattahoochee, and Ochlockonee River systems with the best populations occurring in the Flint River from Decatur County upstream to approximately Peach County. In addition, the Purple Bankclimber has been collected in Ichawaynochaway Creek and an individual weathered shell was collected in Mercer Mill Creek in 2017.
Insufficient water flow in the lower Flint River basin may be impacting undiscovered populations that occur in some creeks in the basin. Excess sedimentation due to inadequate riparian buffer zones covers suitable habitat and could potentially bury mussels. In addition, passage of Gulf Sturgeon through Woodruff Dam may limit dispersal of the species between existing populations. Direct and indirect competition by the introduced Flathead Catfish may be reducing native mussel populations through direct consumption of mussels and their host fishes.
| Threat 1 | Threat 2 | Threat 3 | |
|---|---|---|---|
| General Threat | Natural system modifications | Natural system modifications | Pollution |
| Specific Threat | Dams & water management/use | Dams & water management/use | None |
The Purple Bankclimber is not known to occur on any state properties in Georgia but has been found in water adjacent to Montezuma Bluff WMA and River Creek WMA. 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.
The current distribution and abundance of the Purple Bankclimber in the mainstem Chattahoochee and Ochlockonee rivers in Georgia warrants further investigation. Additional studies may be needed to determine the influence of drought and water withdrawals on this species. Reintroduction or passage of Gulf Sturgeon into the Flint and Chattahoochee Rivers upstream of Woodruff Dam may help increase the abundance of the species within these rivers as well as allow population growth in the Apalachicola River in Florida.
Brim Box, J. and J.D. Williams. 2000. Unionid mollusks of the Apalachicola basin in Alabama, Florida, and Georgia. Alabama Museum of Natural History Bulletin 21. 143 pp.
Fritts, A.K., M.W. Fritts II, D.L. Peterson, D.A. Fox, and R.B. Bringolf. 2012. Critical linkage of imperiled species: Gulf Sturgeon as host for Purple Bankclimber mussels. Freshwater Science 31:1223-1232.
O’Brien, C.A. and J.D. Williams. 2002. Reproductive biology of four freshwater mussels (Bivalvia: Unionidae) endemic to the eastern Gulf Coastal Plain drainages of Alabama, Florida, and Georgia. American Malacological Bulletin 17: 147-158.
Shea, C.P., J.T. Peterson, M.J. Conroy, and J.M. Wisniewski. 2013. Evaluating the influence of land use, drought, and reach isolation on the occurrence of freshwater mussel species in the lower Flint River Basin, Georgia (U.S.A.). Freshwater Biology 58:382-395.
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., R.S. Butler, G.L. Warren, and N.A. Johnson. 2014. Freshwater Mussels of Florida. University of Alabama Press, Tuscaloosa, Alabama.
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
2018-03-16
