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Anodontoides radiatus

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA MOLLUSCA BIVALVIA UNIONOIDA UNIONIDAE

Scientific Name: Anodontoides radiatus
Species Authority: (Conrad, 1834)
Common Name(s):
English Rayed Creekshell
Taxonomic Notes: This taxon has been placed in six genera (Brim Box and Williams 2000). Anodontoides radiatus has been confused with Strophitus subvexus by some investigators. Clench and Turner (1956) reported Anodontoides elliottii from the Apalachicola, Chipola and Chattahoochee drainages. Although Clench and Turner's records of A. elliottii from the Chattahoochee River and Apalachicola River system (Mosquito Creek) are in fact A. radiatus, Johnson (1967) correctly re-identified their Chipola River records as S. subvexus.

A list of synonyms for this species can be found on The MUSSEL project web site (Graf and Cummings 2011).

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2011
Date Assessed: 2011-07-22
Assessor(s): Cummings, K. & Cordeiro, J.
Reviewer(s): Böhm, M. & Collen, B.
Contributor(s): Dyer, E., Soulsby, A.-M., Whitton, F., McGuinness, S., De Silva, R., Milligan, H.T., Kasthala, G., Herdson, R., Thorley, J., McMillan, K. & Collins, A.
Justification:
Anodontoides radiatus has been assessed as Near Threatened. The species was historically rare in large parts of its range, and recent surveys suggest further reductions in both the number of sites where it occurs as well as the number of individuals found per occurrence; the decline in extent of occurrence is likely not above 30%; however, based on this and declines in the number of individuals, and using a precautionary approach, a population decline of 20-25% has been inferred for this species over the past 30 years (estimated to be equal to three generations fo this species). The reasons for this decline are unknown. The species is therefore nearly qualifying for Vulnerable under criterion A2, although it has to be noted that some new sites have been uncovered recently (about a dozen) in Alabama as well as one in Florida where it was formerly thought extirpated. The species can also still be found in all the southeastern states where it was previously known.
History:
1996 Lower Risk/near threatened (Baillie and Groombridge 1996)

Geographic Range [top]

Range Description: Anodontoides radiatus is extant in widespread isolated populations in much of its historical range (Williams et al. 2008). This species occurs in most Gulf Coast drainages from the Apalachicola Basin, Alabama, Florida and Georgia (Brim Box and Williams 2000), west to the Amite River system, Lake Pontchartrain drainage, Louisiana (Vidrine 1993), including the Mobile Basin, where it is widespread below the Fall Line. There are also a few records from above the Fall Line. East of Mobile Basin, it is found in the Escambia, Choctawhatchee, Chipola and Chattahoochee River drainages.

A disjunct population is found in the upper reaches of the Yazoo River drainage of the Mississippi Basin in Mississippi (Haag et al. 2002, Williams et al. 2008). It occurs in the Tombigbee-Alabama River system in Alabama and Mississippi, and the Conecuh-Escambia system in Alabama (Heard 1975), although there are no known records of its occurrence from the latter drainage in Florida. Johnson (1967) claimed it was absent from the intervening Choctawhatchee River system and the Chipola River of the Apalachicola River system. Blalock-Herod et al. (2005) confirm this distribution gap in the Choctawhatchee River drainage based on historical literature, but also found twelve new sites (eleven in Alabama, one in Florida) during recent survey efforts, mostly in small tributaries.


Countries:
Native:
United States (Alabama, Florida, Georgia, Louisiana, Mississippi)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: While its range covers portions of five southeastern states (Alabama, Florida, Georgia, Louisiana, and Mississippi), this species' occurrence is sporadic. In the ACF Basin this species was historically known from 21 occurrences, but in a recent survey it was found at only four of 324 sites surveyed (Brim Box and Williams 2000). Historical sites cited by Johnson (1967) include: ALABAMA-COOSA RIVER SYSTEM - Tombigbee River drainage: Mississippi, Alabama; Coosa River drainage: Alabama; Alabama River drainage: Alabama; ESCAMBIA RIVER SYSTEM- Conecuh River drainage: Alabama; Chattahoochee and Flint River drainages: Georgia; Apalachicola River drainage: Florida. In the Escambia River drainage, it was historically collected at ten occurrences from the main stem and tributaries of the Conecuh River. During a recent survey of the Escambia and Yellow rivers, it was found at six sites, but was not collected at any of the historical localities resurveyed, and now appears to be confined to small, isolated tributaries in Alabama (Brim Box and Williams 2000). The authors therefore consider this species to be threatened in the Escambia River drainage (see also Williams et al. 2008). In another recent survey of the Pea River system (Choctawhatchee River system), it was found at one of approximately 50 sites surveyed (Blalock et al. 1998). Blalock-Herod et al. (2005) confirmed the distribution gap in the Choctawhatchee River drainage based on historical literature, but did find twelve new sites (eleven in Alabama, one in Florida) there during recent survey efforts, mostly in small tributaries. Recent historical data reports exist for the Choctawhatchee River drainage in Alabama/Florida, but Pilarczyk et al. (2006) surveyed 24 sites in 2004 and did not find this species. In the Coosa River basin in Georgia, the species is known historically from the Etowah and Oostanaula River, drainages but has not been collected live recently (Williams and Hughes 1998). Vidrine (1993) cited Louisiana distribution as western Louisiana as well as the Taucipano River in eastern Louisiana, among other scattered locations. Brown and Banks (2001) list 1990s eastern Louisiana records for the Amite and Tangipahoa Rivers. In the Alabama and Mobile basin, it is widespread in the Mobile Basin below the Fall Line with a few records from above; east of Mobile Basin it is found in the Escambia Choctawhatchee, Chipola, and Chattahoochee River drainages. (Williams et al. 2008), although surveys in the Chipola River, reported on in Brim Box and Williams (2000; the species was mistakenly listed as Strophites subvexus) have not reported any specimens.

There is little known about the historical abundance of this species. Museum records suggest that historically it was seldom collected in large numbers and that its occurrence was sporadic throughout its current range. Today, it is unusual to find more than a few individuals at a site. Clench and Turner (1956) noted that Anodontoides radiatus was "exceedingly rare" in the ACF Basin; based on the results of a recent survey, it was assigned a conservation status of endangered in the basin (Brim Box and Williams 2000). Heard (1975) listed A. radiatus among species he considered to have a reduced range or abundance (i.e., are now very rare or extinct in part of their present or past range, respectively). Williams et al. (1993) considered the species to be of special concern throughout its range, indicating that it should be carefully monitored. One of the largest collections of A. radiatus was made by H. H. Smith on 25 June 1915 in Uchee Creek (Russell County, Alabama). The collection totalled 24 individuals (Brim Box and Williams 2000). In a recent survey of the Escambia River drainage, fifteen live individuals were collected from six sites in upper tributaries (Brim Box and Williams 2000), while a single live individual was found in the Pea River watershed (Blalock et al. 1998).

Given its sporadic historical occurrence and what is known about declines over the past 30 years (i.e., likely to equate three generations), as well as using a precautionary approach, a 20-25% decline has been inferred in the population of this species.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Although the Rayed Creekshell is known from large rivers, most collections are from small to medium-sized creeks where it occurs in mud, sand, or gravel substrates in slow to medium currents (Clench and Turner 1956, Jenkinson 1973, Heard 1979, Williams et al. 2008).

Although the lifespan of the species is not known, Harrigan et al. (2009) found the lifespan of the related A. ferussacianus to be 3-16 years, with an average lifespan of 9 years. As such it is reasonable to assume a generation length of around ten years and assess any population declines over a period of three generations, i.e. 30 years.
Systems: Freshwater

Threats [top]

Major Threat(s): Sedimentation as a result of bank destabilization, run-off from agricultural areas, and pollutants (from point and non-point sources) are major threats. Overall stream modifications also threaten survival of this species.

Conservation Actions [top]

Conservation Actions: Williams et al. (2008) stated that Anodontoides radiatus was listed as a species of special concern throughout its range by Williams et al. (1993) and in Alabama by Lydeard et al. (1999). Garner et al. (2004) designated A. radiatus a species of high conservation concern in the state. In the updated AFS (American Fisheries Society) assessment, the species is listed as "vulnerable" (Williams et al. in press, from K. Cummings pers. comm. 2011). Further research is required in order to clarify the taxonomy, population status, ecology and threats impacting this species. Site and habitat protection, species recovery plans, conservation management policies and site management is necessary in order to prevent declines in global population numbers.

Citation: Cummings, K. & Cordeiro, J. 2011. Anodontoides radiatus. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 21 August 2014.
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