endemic to a single nation
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: (5000-20,000 square km (about 2000-8000 square miles)) The Choctaw bean was originally thought to be endemic to the Escambia, Yellow, and Choctawhatchee River drainages in Alabama and Florida (Williams and Butler, 1994; Johnson, 1967). Due to recent status surveys the historical range of the Choctaw bean has been expanded (Williams et al., 2000; Blalock-Herod et al., 2005). The species is restricted to Gulf Coast drainages from the Choctawhatchee River west to the Escambia River in southeastern Alabama and western Florida (Williams et al., 2008).
Length: 4.9 cm
Small size, subelliptical outline, low rounded posterior ridge, brownish with some fine green rays on the umbone, females truncate, males evenly rounded posteriorly.
Habitat Type: Freshwater
Comments: The Choctaw bean is known from large creeks and rivers with moderate current over sand to silty-sand substrates (Deyrup and Franz, 1994; Williams and Butler, 1994).
Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: No. No populations of this species make annual migrations of over 200 km.
Adults are essentially sessile. About the only voluntary movement they make is to burrow deeper into the substrate although some passive movement downstream may occur during high flows. Dispersal occurs while the glochidia are encysted on their host (probably a fish).
Comments: Presumably fine particulate organic matter, primarily detritus, and/or zooplankton, and/or phytoplankton (Fuller, 1974). Larvae (glochidia) of freshwater mussels generally are parasitic on fish and there may be a specificity among some species.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 21 - 80
Comments: Due to recent status surveys the historical range of the Choctaw bean has been expanded (Williams et al., 2000; Blalock-Herod et al., 2005). Within the Escambia River drainage, it is known from the Escambia River, Escambia County, Florida; Murder Creek, Conecuh County, Patsaliga and Little Patsaliga Creeks, Crenshaw County; and Pigeon Creek, Butler County, all in Alabama. Within the Yellow River drainage, it is known from the main channel Yellow River in Okaloosa County, Florida, and Covington County, Alabama. Within the Choctawhatchee River drainage, the Choctaw bean is known from the Choctawhatchee River main stem in Washington and Holmes Counties, Florida; and the Pea River, Geneva County, Alabama (Williams et al., 2000; Blalock-Herod et al., 2005) (see USFWS, 2003; Butler, 1989). Recent mussel status surveys found that populations (live and shell material only) of the Choctaw bean have declined from 13 historic sites to 7 currently active sites, 4 inactive, and 2 with an undetermined population status within the Escambia River drainage; it has declined from 6 historic sites to 5 currently active sites and 1 with an undetermined population status within the Yellow River drainage; and from 26 historic sites to 22 currently active sites, 1 inactive site, and 3 sites with undetermined population status within the Choctwhatchee River drainage (fide Williams et al., 2000; Blalock-Herod et al., 2005). Blalock-Herod et al. (2005) listed it in 6 historical (found in 2 of 3 recently resurveyed) and 20 new sites in the Choctawhatchee River drainage of Alabama (mostly) and Florida. Pilarczyk et al. (2006) recorded recent collections (in 2004) of this species following surveys of 24 sites at three sites in Alabama including West Fork Choctawhatchee River, Pea Creek, and East Fork Choctawhatchee River compared to Patsaliga Creek, Yellow River, Pea River, Pea Creek, West Fork Choctawhatchee River, Judy Creek, and East Fork Choctawhatchee River in surveys of the same sites in the 1990s. Gangloff and Hartfield (2009) found it in 3 Pea River sites and 1 Choctawhatchee River sites in Alabama.
2500 - 10,000 individuals
Comments: Eleven per hour were collected in 1988 at the best known site at the time. It is generally known from fair numbers from most sites represented in museum lots, including several series of paratypes. It was considered rare in the Choctawhatchee River (Florida) by Heard (1975); and recent surveys in that area by Pilarczyk et al. (2006) recorded recent collections (in 2004) of this species following surveys of 24 sites at three sites in Alabama including West Fork Choctawhatchee River (31 live), Pea Creek (10 live), and East Fork Choctawhatchee River (3 live) compared to Patsaliga Creek, Yellow River, Pea River, Pea Creek, West Fork Choctawhatchee River, Judy Creek, and East Fork Choctawhatchee River in surveys of the same sites in the 1990s (with an average of 2 individuals found live per site (Blalock-Herod et al., 2005).
Found in sometimes difficult-to-collect larger streams, which probably accounts for its relatively recent discovery. It has one of the most restricted ranges of any member of the genus.
Life History and Behavior
Probably tachytictic (short-term brooder) as are other, more northerly members of the genus.
Date Listed: 10/10/2012
Lead Region: Southeast Region (Region 4)
For most current information and documents related to the conservation status and management of Villosa choctawensis, see its USFWS Species Profile
National NatureServe Conservation Status
Rounded National Status Rank: N2 - Imperiled
NatureServe Conservation Status
Rounded Global Status Rank: G2 - Imperiled
Reasons: This species, although still maintaining the same range extent, this species has a limited distribution, restricted habitat, decreasing numbers of extant occurrences, questionable viability of certain extant occurrences and overall deteriorating habitat and water quality.
Intrinsic Vulnerability: Highly to moderately vulnerable.
Comments: Thought to be fairly sensitive to siltation and habitat modifications; typical liabilities of filter-feeders (e.g., to pollutants, eutrophication, etc.); disappearance of host fish a potential problem as is the extreme habitat fragmentation hindering dispersal capability.
Environmental Specificity: Unknown
Other Considerations: Considering its small size and affinity for large stream channels, this species may have been overlooked in past collections. Considered threatened throughout its range (Williams et al., 1993), threatened in Florida (Deyrup and Franz, 1994), and endangered in the Escambia and Yellow River systems (Williams et al., 2000).
Global Short Term Trend: Decline of 10-30%
Comments: Recent status surveys indicated that this species has experienced range reductions and occurs in low abundance within its limited range. In totality, the Choctaw bean has declined from a total of 45 historic sites to its remaining distribution of 34 sites. It has been extirpated from approximately 11% of its historic range. An average of 2 individuals were found live per site (fide Williams et al., 2000; Blalock-Herod et al., 2005. Two gravid individuals have been detected, but recent recruitment has not been confirmed (fide Williams et al., 2000). The longterm viability of the Choctaw bean is questionable (see USFWS, 2003). Blalock-Herod et al. (2005) listed it in 6 historical (found in 2 of 3 recently resurveyed) and 20 new sites in the Choctawhatchee River drainage of Alabama (mostly) and Florida. Pilarczyk et al. (2006) recorded recent collections (in 2004) of this species following surveys of 24 sites at three sites in Alabama including West Fork Choctawhatchee River, Pea Creek, and East Fork Choctawhatchee River compared to Patsaliga Creek, Yellow River, Pea River, Pea Creek, West Fork Choctawhatchee River, Judy Creek, and East Fork Choctawhatchee River in surveys of the same sites in the 1990s.
Global Long Term Trend: Relatively stable to decline of 50%
Comments: Johnson (1967) lists historical sites in: CHOCTAWHATCHEE RIVER SYSEM- Pea River drainage: Pea River, Alabama; Choctawhatchee River drainage: Florida. The Choctaw bean appears to be extirpated from Murder Creek, Conecuh County; Pigeon Creek, Butler County; and Little Patsaliga Creek, Crenshaw County, all Alabama, all Escambia River basin; and Choctawhatchee River, Holmes County, Florida. Butler (1989) listed the following sites: Yellow River mainstem, Alabama; east of Blackman, Florida. Butler (1989) also listed Escambia River localities including Piegeon Creek, Alabama; Patsaliga River, Alabama; Little Patsaliga Creek, Alabama. The Choctaw bean appears to be extirpated from Murder Creek, Conecuh County; Pigeon Creek, Butler County; and Little Patsaliga Creek, Crenshaw County, all Alabama, all Escambia River basin; and Choctawhatchee River, Holmes County, Florida. Recent status surveys indicated that this species has experienced range reductions and occurs in low abundance within its limited range. In totality, the Choctaw bean has declined from a total of 45 historic sites to its remaining distribution of 34 sites. It has been extirpated from approximately 11% of its historic range (see USFWS, 2003).
Degree of Threat: High
Comments: Premier threat is habitat loss or degradation. The stream and river habitats are vulnerable to habitat modification, sedimentation, and water quality degradation from a number of activities. Highway and reservoir construction, improper logging practices, agricultural runoff, housing developments, pipeline crossings, and livestock grazing often result in physical disturbance of stream substrates or the riparian zone, and/or changes in water quality, temperature, or flow. Sedimentation can cause direct mortality of mussels by deposition and suffocation (Ellis, 1936; Brim Box and Mossa, 1999) and can eliminate or reduce the recruitment of juvenile mussels (Negus, 1966; Brim Box and Mossa, 1999). Suspended sediment can also interfere with feeding activity of mussels (Dennis, 1984). Many of the confirmed extant populations of this species are in the vicinity of highway and unpaved road crossings due to ease of access for surveyors. Highway and bridge construction and widening could affect populations of these species unless appropriate precautions are implemented during construction to reduce erosion and sedimentation, and maintain water quality standards. The construction of reservoirs and the associated habitat changes (e.g., changes of sediments, flow, water temperature, dissolved oxygen) can directly impact mussel populations (Neves et al., 1997). Nutrients, usually phosphorus and nitrogen, may emanate from agricultural fields, residential lawns, livestock feedlots, poultry houses, and leaking septic tanks in levels that result in eutrophication and reduced oxygen levels in small streams. Other factors include (1) over-utilization for commercial, recreational, scientific, or educational purposes (note: species is not commercially valuable nor are the streams and rivers it inhabits subject to harvesting activities for commercial mussel species), (2) disease or predation (poorly known but may contribute to the further decline of these species due to their restricted distributions and low numbers associated with extant populations), (3) the inadequacy of existing regulatory mechanisms (note: less success in dealing with non-point source pollution impacts, particularly sediments, to small stream drainages), (4) catastrophic events (populations are generally small and geographically isolated; the round ebonyshell and southern kidneyshell are vulnerable to catastrophic events because of low population numbers known from 3 and 2 sites), (5) host fish loss or decline (note host not known), (6) populations below effective population size to maintain long term viability (some populations below required population size to maintain long-term genetic viability), (7) invasive species (Asiatic clam, zebra mussel, black carp) (see U.S. Fish and Wildlife Service, 2003).
Biological Research Needs: Determine reproductive biology (i.e., host fish(s)); propagation techniques; consider federal protection; determine life history, fecundity, viability of extant populations, microhabitat requirements, sensitivity to silt, excessive nutrients, and pollutants; determine competitive interactions with Corbicula.
Global Protection: None. No occurrences appropriately protected and managed
Comments: There are probably no protected occurrences of this species, although at least one occurrence may border the Conecuh National Forest.
Needs: Protect species by federal listing, acquisitions and easements by working with government agencies and conservation organizations; establish buffers and streamside management zones for all agricultural, silvicultural, mining, and developmental activities; propagate for reintroduction into restored habitats; maintain high water and benthic habitat quality; control/eradicate Corbicula populations. Conservation activities have been limited to working with private landowners in south Alabama and west Florida to encourage the use of Best Management Practices to reduce the effects of agriculture and silviculture. (see U.S. Fish and Wildlife Service, 2003)
Relevance to Humans and Ecosystems
Stewardship Overview: This species has been listed as a federal candidate species for endangered species status in the U.S. (USFWS, 2003). Conservation activities have been limited to working with landowners in west Alabama and south Florida to limit the effects of agricultural practices on populations. This species has probably been negatively affected greatest by poor land use practices resulting in habitat destruction and leading to decline and imperilment.
The Choctaw bean, scientific name Villosa choctawensis, is a species of freshwater mussel, an aquatic bivalve mollusc in the family Unionidae. This species is found in the southeastern United States and is currently on the endangered species list. The species epithet and the common name are based on the name of the Choctaw people, Native Americans who were originally from the southeastern United States.
- "Choctaw bean species profile". U.S. Fish and Wildlife Service. May 22, 2013.
|This bivalve-related article is a stub. You can help Wikipedia by expanding it.|