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Elliptio arctata (Conrad, 1834)
Delicate Spike
Federal Protection: No US federal protection
State Protection: Endangered
Global Rank: G2G3
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: 69
Habitat Summary for element in Georgia: Creeks and rivers with moderate current; mainly in crevices and under large rocks in silt deposits
Typically compressed to moderately inflated shell, elliptical or elongate in shape. Maximum length is approximately 3.5 inches (90 mm). Anterior margin is broadly rounded while posterior margin is typically rounded to biangulate. Ventral margin relatively straight to slightly arcuate. Posterior ridge sharply angular to round in larger individuals. Umbos slightly projecting above hingeline. Periostracum typically dark brown to black in adults. Juveniles may be yellow to green with fine rays near the umbo. Left valve with two triangular stumpy pseudocardinal teeth and two low and straight lateral teeth. Right valve with one low, serrated pseudocardinal tooth and one typically high, straight, and long lateral tooth. Umbo cavity typically shallow and wide. Nacre variable but typically bluish white to salmon.
Alabama Spike (Elliptio arca). The Delicate Spike can be distinguished from the Alabama Spike by the former typically having a thinner shell and shorter length. Furthermore, the Delicate Spike is typically more inflated and has heavier teeth.
Gravel or sand shoals in medium to large rivers. Occasionally found in sand-bottomed runs with slow, steady current. Usually found adjacent to or underneath large boulders or limestone bedrock in center channel; rarely found in slack water or silt.
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 (Vaugh and Hakenkamp 2001).
The life history of this species is poorly understood, but females are believed to brood glochidia in the spring or summer. Glochidial hosts are unknown.
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.
Historically widespread from the Apalachicola River Basin west to the Pearl River in Mississippi, but becoming more restricted throughout its range. Within Georgia, the Delicate Spike historically occurred in the Mobile and Apalachicola River basins, above and below the Fall Line. It currently appears to be extremely rare or extirpated in the Mobile River basin of Georgia. Only three recent collections of live individuals have been made and few shells have been collected despite extensive sampling in the Conasauga, Coosawattee, and Oostanaula rivers. In the Apalachicola River basin, this species appears to be restricted to the Flint River and its tributaries. The Delicate Spike has also been reported from the Atlantic Slope of Georgia, but this report may be of a different or unrecognized species.
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. Incompatible dam operations on the Coosawattee River may be affecting downstream unionids. Excessive agriculture water pumping in the Lower Flint River basin may be affecting individuals occupying smaller streams prone to drying during periods of extreme drought.
| Threat 1 | Threat 2 | Threat 3 | |
|---|---|---|---|
| General Threat | Pollution | Natural system modifications | None |
| Specific Threat | Agricultural & forestry effluents | Dams & water management/use | None |
The Delicate Spike is not known from any state or federal lands in Georgia. However, the Delicate Spike is include as on of the focal species of the Altamaha Candidate Conservation Agreement between the Georgia Power Company, US Fish and Wildlife Service, and the Wildlife Resources Division. 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 of this species in the 2015 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. Investigation of the taxonomy of the Delicate Spike to determine determining if individuals collected from across the known range are the same species was identified as a top research priority in the 2015 Georgia Wildlife Action Plan.
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.
Evans, R.R. 1998. Historical and contemporary distributions of aquatic mollusks in the upper Conasauga River system of Georgia and Tennessee. M.S. Thesis. University of Tennessee at Chattanooga. 277 pp.
Garner, J.T. Elliptio arctata Delicate Spike. 2004. Pp. 45 in R.E. Mirarchi, J.T. Garner, M.F. Mettee, P.E. O’Neil (eds.). Alabama Wildlife, Volume 2, Imperiled Aquatic Mollusks and Fishes. The University of Alabama Press, Tuscaloosa.
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., A.E. Bogan, and J.T. Garner. 2008. Freshwater mussels of Alabama and the Mobile Basin in Georgia, Mississippi, and Tennessee. The University of Alabama Press, Tuscaloosa.
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
2008-09-01
update 2021-10-05
