Roadless Areas
Home/Species/ Southern Elktoe

Alasmidonta triangulata

(I. Lea, 1858)

Southern Elktoe

G1Critically Imperiled Found in 1 roadless area NatureServe Explorer →
G1Critically ImperiledGlobal Rank
EndangeredIUCN
Very highThreat Impact
Southern elktoe (Alasmidonta triangulata). Photo by U.S. Fish & Wildlife Service, Public Domain (U.S. Government Work), via ECOS.
U.S. Fish & Wildlife Service, https://www.usa.gov/government-works
Identity
Unique IDELEMENT_GLOBAL.2.114679
Element CodeIMBIV02080
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryInvertebrate Animal
IUCNEndangered
Endemicendemic to a single nation
KingdomAnimalia
PhylumMollusca
ClassBivalvia
OrderUnionoida
FamilyUnionidae
GenusAlasmidonta
Concept Reference
Turgeon, D. D., J. F. Quinn, Jr., A. E. Bogan, E. V. Coan, F. G. Hochberg, W. G. Lyons, P. M. Mikkelsen, R. J. Neves, C. F. E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F. G. Thompson, M. Vecchione, and J. D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland. 526 pp.
Taxonomic Comments
Although Clarke (1981) considered Alasmidonta triangulata as a synonym of A. undulata, most authors recognize it as a distinct species (Clench and Turner 1956, Johnson 1970, Turgeon et al. 1998, Brim Box and Williams 2000, Williams et al. 2017. Further genetic studies may help to elucidate relationships within the genus.
Conservation Status
Rank Method Rank calculation - Biotics v2
Review Date2021-01-26
Change Date2013-09-24
Edition Date2021-01-26
Edition AuthorsJackson, D. R. (2021); Cordeiro, J. (2011)
Threat ImpactVery high
Range Extent1000-5000 square km (about 400-2000 square miles)
Number of Occurrences1 - 5
Rank Reasons
The species is restricted to the Apalachicola-Chipola river system (many sites representing a single large occurrence), and has suffered severe declines. Populations apparently are very small at all known sites. The Apalachicola drainage is subject to multiple threats, including dredging activities, impoundment, pollution, and excess water withdrawal for human use and consumption.
Range Extent Comments
This species is restricted to the Apalachicola River system, where it was found historically in the Chattachoochee and Flint rivers of Alabama and Georgia, and the Apalachicola and Chipola rivers of Florida. It is unlikely that it survives in Lake Seminole, the upstream impounded portion of the Apalachicola River.
Occurrences Comments
In Florida, from 2010-2020, small numbers have been found live at 18 sites (Chipola and Apalachicola rivers) (unpublished records compiled by U.S. Fish and Wildlife Service 2020; provided to FNAI). In Alabama, it was last reported from (and is still extant in) Uchee and Little Uchee creeks in Russell and Lee counties (Mirarchi et al. 2004; Williams et al. 2008). Flint River, Upson County, Georgia specimens identified by Athearn (1998) as A. wrightiana may also be A. triangulata (Johnson 1967).
Threat Impact Comments
This species is threatened by siltation and chemical runoff from poorly conducted agricultural, silvicultural, mining, and developmental (e.g., bridge, dam, culvert, boat ramp, and road construction) activities; localized municipal pollution; impoundment and habitat fragmentation from dams; excessive water (surface and groundwater) withdrawal (especially during drought) for human uses; and competition from non-native invasive clams and mussels are considered the major current threats to riverine mussels in Florida. However, projected global warming may threaten most native freshwater mussel species in the southeastern U.S. through increased juvenile mortality at high water temperatures (Ganser et al. 2013). The Apalachicola River is subject to many of these threats; perhaps most severe is excessive water withdrawal to support the Atlanta, Georgia, metropolitan area. Harvest of small numbers of this species for personal use (fish bait) is permitted by the Florida Mussel Rule (68A-23.015 F.A.C.), which was passed to protect unionid mussels from the larger threat of commercial harvest.
Ecology & Habitat

Habitat

This species is found in big rivers (e.g. mainstem Apalachicola) in muddy sand with moderate current (Heard, 1979). Historically, this species was found in larger creeks and river mainstems and seemed to prefer sandy mud, particularly in and around rock pools (Clench and Turner, 1956). In Chattahoochee River tributaries, it was found in sand bars, but was absent near rocks or in muddy sediments. Brim Box and Williams (2000) found two live specimens in a sand and silt substrate.

Reproduction

The glochidial host is unknown.
Other Nations (1)
United StatesN1
ProvinceRankNative
GeorgiaS1Yes
FloridaS1Yes
AlabamaS1Yes
Threat Assessments
ThreatScopeSeverityTiming
2 - Agriculture & aquacultureLarge (31-70%)Serious or 31-70% pop. declineHigh (continuing)
3 - Energy production & miningLarge (31-70%)Serious or 31-70% pop. declineHigh (continuing)
7 - Natural system modificationsLarge (31-70%)Serious or 31-70% pop. declineHigh (continuing)
7.2 - Dams & water management/useLarge (31-70%)Serious or 31-70% pop. declineHigh (continuing)
8 - Invasive & other problematic species, genes & diseasesPervasive (71-100%)Extreme or 71-100% pop. declineHigh (continuing)
8.1 - Invasive non-native/alien species/diseasesPervasive (71-100%)Extreme or 71-100% pop. declineHigh (continuing)
9 - PollutionLarge (31-70%)Moderate or 11-30% pop. declineHigh (continuing)
9.1 - Domestic & urban waste waterLarge (31-70%)Moderate or 11-30% pop. declineHigh (continuing)
9.2 - Industrial & military effluentsRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
9.3 - Agricultural & forestry effluentsRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
11 - Climate change & severe weatherRestricted (11-30%)Moderate or 11-30% pop. declineModerate (short-term)
11.2 - DroughtsRestricted (11-30%)Moderate or 11-30% pop. declineModerate (short-term)

—

Roadless Areas (1)
Florida (1)
AreaForestAcres
SavannahApalachicola National Forest1,927
References (35)
  1. Athearn, H. D. 1998. Additional records and notes on the unionid fauna of the Gulf Drainage of Alabama, Georgia, and Florida. Occasional Papers on Mollusks 5(76):465-467.
  2. Battle, J., S.W. Golladay, and A.R. Bambarger. 2003. Mussel conservation in the Chickasawhatchee and Elmodel Wildlife Management Areas: methods for a relocation study. Pages 860-863 in K.J. Hatcher (ed.) Proceedings of the Georgia Water Resources Conference, Institute of Ecology, The University of Georgia, Athens, Georgia.
  3. 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: 1-143.
  4. Clarke, A.H. 1981a. The freshwater mollusks of Canada. National Museum of Natural Sciences, National Museums of Canada, D. W. Friesen and Sons, Ltd.: Ottawa, Canada. 446 pp.
  5. Clarke, A. H. 1981. The tribe Alasmidontini (Unionidae: Anodontinae), Part I: <i>Pegias</i>, <i>Alasmidonta</i>, and <i>Arcidens</i>. Smithsonian Contributions to Zoology 326:1-101.
  6. Clench, W. J. and R. D. Turner. 1956. Freshwater mollusks of Alabama, Georgia, and Florida from the Escambia to the Suwanee River. Bulletin of the Florida State Museum Biological Sciences 1(3):97-239.
  7. Deyrup, M., and R. Franz (Eds.). 1994. Rare and Endangered Biota of Florida, Volume IV. Invertebrates. University Press of Florida, Gainesville, Florida. 798 pp.
  8. Freshwater Mollusk Conservation Society (FMCS). 2023. The 2023 checklist of freshwater bivalves (Mollusca: Bivalvia: Unionida) of the United States and Canada. Considered and approved by the Bivalve Names Subcommittee October 2023. Online: https://molluskconservation.org/MServices_Names-Bivalves.html
  9. Ganser , A. M., T. J. Newton, and R. J. Haro.  2013.  The effects of elevated water temperature on native juvenile mussels: implications for climate change.  Freshwater Science 32(4):1168-1177.
  10. Graf, D.L. and K.S. Cummings. 2021. A 'big data' approach to global freshwater mussel diversity (Bivalvia: Unionoida), with an updated checklist of genera and species. Journal of Molluscan Studies 87(1):1-36.
  11. Heard, W.H. 1979. Identification manual of the fresh water clams of Florida. State of Florida, Department of Environmental Regulation, Technical Series, 4(2): 1-82.
  12. Howard, A. D. 1915. Some exceptional cases of breeding among the Unionidae. The Nautilus 29:4-11.
  13. Johnson, R. I. 1967. Additions to the Unionid fauna of the Gulf Drainage of Alabama, Georgia and Florida (Mollusca: Bivalvia). Breviora 270:1-21.
  14. Johnson, R.I. 1970a. The systematics and zoogeography of the Unionidae (Mollusca: Bivalvia) of the southern Atlantic slope region. Bulletin of the Museum of Comparative Zoology, Harvard University 140(6): 263-449.
  15. Johnson, R.I. 1972a. The Unionidae (Mollusca: Bivalvia) of peninsular Florida. Bulletin of the Florida State Museum of Biological Science 16(4): 181-249.
  16. Lefevre, G. and W. T. Curtis. 1912. Studies on the reproduction and artificial propagation of fresh-water mussels. Bulletin of the Bureau of Fisheries 30:102-201.
  17. Mirarchi, R.E., J.T. Garner, M.F. Mettee, and P.E. O'Neil. 2004b. Alabama wildlife. Volume 2. Imperiled aquatic mollusks and fishes. University of Alabama Press, Tuscaloosa, Alabama. xii + 255 pp.
  18. MolluscaBase eds. 2024. MolluscaBase. Accessed at https://www.molluscabase.org
  19. Moyle, P., and J. Bacon. 1969. Distribution and abundance of molluscs in a fresh water environment. Journal of the Minnesota Academy of Science 35(2/3):82-85.
  20. Ortmann, A.E. 1919. Monograph of the naiades of Pennsylvania. Part III. Systematic account of the genera and species. Memoirs of the Carnegie Museum 8(1):1-385.
  21. Strayer, D. 1983. The effects of surface geology and stream size on freshwater mussel (Bivalvia, Unionidae) distribution in southeastern Michigan, U.S.A. Freshwater Biology 13:253-264.
  22. Strayer, D.L. 1993. Macrohabitats of freshwater mussels (Bivalvia: Unionacea) in streams of the northern Atlantic Slope. Journal of the North American Benthological Society, 12(3): 236-246.
  23. Strayer, D. L. 1999. Use of flow refuges by unionid mussels in rivers. Journal of the North American Benthological Society 18(4):468-476.
  24. Strayer, D. L., and J. Ralley. 1993. Microhabitat use by an assemblage of stream-dwelling unionaceans (Bivalvia) including two rare species of <i>Alasmidonta</i>. Journal of the North American Benthological Society 12(3):247-258.
  25. Turgeon, D. D., J. F. Quinn, Jr., A. E. Bogan, E. V. Coan, F. G. Hochberg, W. G. Lyons, P. M. Mikkelsen, R. J. Neves, C. F. E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F. G. Thompson, M. Vecchione, and J. D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland. 526 pp.
  26. U.S. Fish and Wildlife Service (USFWS). 2011. Endangered and threatened wildlife and plants; partial 90-day finding on a petition to list 404 species in the southeastern United States as threatened or endangered with critical habitat. Federal Register 76(187):59836-59862.
  27. U.S. Fish and Wildlife Service (USFWS). 2023. Endangered and Threatened Wildlife and Plants; Endangered Species Status for Southern Elktoe and Designation of Critical Habitat. Proposed rule. Federal Register 88(118):40160-40189.
  28. U.S. Fish and Wildlife Service (USFWS). 2025. Endangered and Threatened Wildlife and Plants; Review of Species That Are Candidates for Listing as Endangered or Threatened; Annual Notification of Findings on Resubmitted Petitions; Annual Description of Progress on Listing Actions. Candidate notice of review (CNOR). Federal Register 90(209):48912-48937.
  29. Van der Schalie, H. 1938. The naiad fauna of the Huron River in southeastern Michigan. Miscellaneous Publication of the Museum of Zoology, University of Michigan 40:7-78.
  30. Watters, G. T. 1992. Unionids, fishes, and the species-area curve. Journal of Biogeography 19:481-490.
  31. Williams, James D., Gainesville, FL. (Retired from: Biological Research Division, U.S. Geological Survey, Gainesville, FL)
  32. Williams, J. D. 2015. Conservation status review of the Southern Elktoe, <i>Alasmidonta triangulata</i>. Final Report submitted to U.S. Fish and Wildlife Service Panama City, Florida. 11 pp.
  33. Williams, J.D., A.E. Bogan, and J.T. Garner. 2008. Freshwater Mussels of Alabama & the Mobile Basin in Georgia, Mississippi & Tennessee. University of Alabama Press: Tuscaloosa, Alabama. 908 pp.
  34. Williams, J. D., A. E. Bogan, R. S. Butler, K. S. Cummings, J. T. Garner, J. L. Harris, N. A. Johnson, and G. T. Watters. 2017. A revised list of the freshwater mussels (Mollusca: Bivalvia: Unionida) of the United States and Canada. Freshwater Mollusk Biology and Conservation 20:33-58.
  35. Williams, J. D., R. S. Butler, G. L. Warren, and N. A. Johnson. 2014a. Freshwater Mussels of Florida. University of Alabama Press, Tuscaloosa, Alabama. 498 pp.