Alasmidonta Arcula, commonly known as the Altamaha Arcmussel, is species of freshwater mussels known to exist in only a few sites in the Altamaha River and its tributaries.   This species is considered rare, owing partially to its limited distribution.  In fact, Johnson (1970) stated that "not more than a few specimens have ever been collected at any station in this century save for a series of twenty-two specimens collected by H. D. Athearn in 1962 in the Ocmulgee River, below Lumber City.”


Foraging Behavior

 

            The Arcmussel is a bivalve mussel and uses a method of filter-feeding to extract organic materials from the environment surrounding them..  These mussels are, for the most part, stationary and infaunal, meaning that they bury themselves in sediment.  It is usually found to live in sandy mud in sluggish water (IUCN 2010). 


Reproductive and Nesting Behavior

 

            Like other mussels, Alasmidonta arcula utilizes a method of external fertilization, which involves larvae becoming attached to a host fish during maturation and later dropping off, leaving the fish unharmed.  Although the host fish for these species has not been scientifically identified, it is suspected that Centrarchids (sunfish) or the striped mullet are likely candidates. 


Major Predators

 

In general, freshwater mussels are eaten by fish, birds, and other marine animals. The main threat to the Alasmidonta arcula appears to be loss of habitat and deterioration in water quality.  There may also be an impact from Corbicula, a genus of freshwater clams, also present in the area, but the effects are currently unknown (IUCN 2010). 


Distribution

 

            The Arcmussel is endemic to one river system in the state of Georgia.  Within the river system, the Arcmussel is known to occur on three tributaries: two sites in the Ocmulgee River, one site in the Ohoopee River, and three sites in the Altamaha River (IUCN 2010).  This species has a range extent of less than 5000 sq. kilometers and a habitat of less than 500 sq. kilometers (Cordeiro 2007).  


Population Status

 

            Because they are stationary creatures and utilize filter-feeding, they have a tendency to “accumulate and concentrate toxins over many years” (USGS Great Lakes Science Center, 2000).  They are also under threat from “loss of habitat and deterioration in water quality” (IUCN 2010).  Historically, this species has been known to exist in 12 occurrences in 4 rivers in Georgia, it is currently only known in 6 sites on one river system (Cordeiro 2007).  This species’ population is thought to be declining and is listed as endangered by the IUCN Red List of Threatened Species.


Status of Current Proposal

 

            The Arcmussel is currently not listed as endangered on the U.S. Fish and Wildlife Services list of endangered species.  In 1994, the Arcmussel status was classified as “unknown” with the statement that “persuasive data on biological vulnerability and threat are not currently unavailable to support proposed rules” (Department of the Interior 1994).   According to the website, no petitions have been published for the Altamaha arcmussel (Department of the Interior 2010). 


            The Arcmussel is listed as endangered by the IUCN Red List of Threatened Species.  The Georgia DNR lists this species as threatened, stating that it is a species “likely to become an endangered species in the foreseeable future throughout all or parts of its range” (Georgia DNR 2010).  Currently, it is listed as imperiled globally and statewide because of rarity (Georgia DNR 2010). 

 

 

Literature Cited

 

Cordeiro, J. [online]. 2007.  NatureServe Explorer: Alasmidonta arcula.

http://www.natureserve.org/explorer/servlet/NatureServe?searchName=Alasmidonta+arcula (23 July 2010).

Georgia DNR [online]. 2010.  Georgia Department of Natural Resources. http://www.gadnr.org

(23 July 2010).

IUCN [online]. 2010. The IUCN Red List of Threatened Species. Version 2010. 1.

http://www.iucnredlist.org (23 July 2010).

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, Harvard University, 140(6): 263-449.

 

USGS Great Lakes Science Center [online]. 2000. North American Freshwater Clams.

<http://www.glsc.usgs.gov/_files/factsheets/2000-5%20Clams.pdf> (24 July 2010).