Margaritifera hembeli - (Conrad, 1838)
Louisiana Pearlshell
Taxonomic Status: Accepted
Related ITIS Name(s): Margaritifera hembeli (Conrad, 1838) (TSN 80373)
Unique Identifier: ELEMENT_GLOBAL.2.112056
Element Code: IMBIV27010
Informal Taxonomy: Animals, Invertebrates - Mollusks - Freshwater Mussels
 
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Bivalvia Unionoida Margaritiferidae Margaritifera
Genus Size: B - Very small genus (2-5 species)
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Concept Reference
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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.
Concept Reference Code: B98TUR01EHUS
Name Used in Concept Reference: Margaritifera hembeli
Taxonomic Comments: The family Margaritiferidae is recognized based on the recent work of Smith (1986) and Smith and Wall (1984). The monotypic genus Cumberlandia has generally has been classified in the family Margaritiferidae; however, preliminary analyses of electrophoretic data led Davis and Fuller to lump the margaritiferids with the Unionidae (Davis and Fuller, 1981). Smith and Wall (1984) reinstated the Margaritiferidae to familial rank following and extensive examination and analysis of morphological characters. Some anatomical data on stomach anatomy (Smith, 1986) indicates Cumberlandia may require reduction to subgeneric level. This is supported by Davis and Fuller (1981), Ziuganov et al. (1994), Smith (2001), and Huff et al. (2004). Smith (2001) analyzied the taxonomic placement of the margaritiferid genera, recognizing Pseudunio, Margaritifera, and Margaritinopsis as valid based largely on morpological characters. Contrary to Smith (2001), Huff et al. (2004) investigated phylogenetic relationships using sequence data from five molecular markers and concluded recognition of of at least Margaritifera margaritifera, Margaritifera laevis, Margaritifera falcata, and Margaritifera auricularia with the following relationships: Cumberlandia + Margaritifera auricularia; Margaritifera falcata (Margaritifera marrianae + Margaritifera laevis); and to a lesser degree Dahurinaia dahurica + Margaritifera margaritifera. Margaritifera hembeli was distinguished from Margaritifera marrianae by Johnson (1983) based on shell morphology and by Smith (1988) based on anatomical differences.
Conservation Status
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NatureServe Status

Global Status: G1
Global Status Last Reviewed: 27Jul2006
Global Status Last Changed: 05Sep2000
Rounded Global Status: G1 - Critically Imperiled
Reasons: This species is restricted to only two river drainages (about 20 occurrences) in central Louisiana, having declined by over 80% in only a few generations time for this long-lived species. This represents a fraction of the admittedly narrow historic range but these populations appear stable although historic occurrences, including all of Arkansas, have been extirpated and declines have been very large.
Nation: United States
National Status: N1 (10Mar1998)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Arkansas (SU), Louisiana (S1)

Other Statuses

U.S. Endangered Species Act (USESA): LT: Listed threatened (24Sep1993)
U.S. Fish & Wildlife Service Lead Region: R4 - Southeast
IUCN Red List Category: CR - Critically endangered
American Fisheries Society Status: Threatened (01Jan1993)

NatureServe Global Conservation Status Factors

Range Extent: 100-250 square km (about 40-100 square miles)
Range Extent Comments: Vidrine (1993) reported this species to be rare from small streams in central Luouisiana and included such sites as Spring Creek (Bayou Cocodrie drainage), Catahoula Ranger District streams flowing into the southern end of the Red River. This species is currently restricted to two subpopulations on opposite sides of the Red River drainage in central Louisiana (Shively, 1999; Vidrine, 1993). Johnson and Brown (1998) claim the species is limited to 22 headwater streams in the Red River basin of central Louisiana. Based on museum records there are indications that it may have historically occurred throughout the headwater streams of the Bayou Boeuf drainage (USFWS, 1989k). Populations in Alabama are now ascribed to Margaritifera marrianae (Johnson, 1983).

Area of Occupancy: 26-500 4-km2 grid cells
Area of Occupancy Comments:  

Number of Occurrences: 6 - 20
Number of Occurrences Comments: Vidrine (1993) reported this species to be rare from small streams in central Louisiana and included such sites as Spring Creek (Bayou Cocodrie drainage), Catahoula Ranger District streams flowing into the southern end of the Red River. A 1998 survey of the streams in Rapides Parish found it extant at 11 streams, and a 1999 survey of the streams in Grant Parish found it extant in 13 streams, but 95% were concentrated in four of these streams (Shively, 1999; Shively and Vermillion, 1998). Johnson and Brown (1998) claim the species is limited to 22 headwater streams in the Red River basin of central Louisiana. Bolden and Brown (2002) utilized specimens from Jordan Creek in the Kisatchie National Forest in central Louisiana for a translocation study.

Population Size: 2500 - 10,000 individuals
Population Size Comments: The number of individuals found at three of the streams in Rapides Parish has been high since 1985 (average estimate is over 2,000 individuals per site) (Shively and Vermillion, 1998). In Grant Parish it was found in 60% of the total stream lengths searched (Shively, 1999). See Shively (1999) and Shively and Vermillion (1998) for more detailed information on abundance. Bolden and Brown (2002) cite it in aggregations of 20 to 40 mussels per square meter and sometimes in beds as dense as 300 per square meter.

Number of Occurrences with Good Viability/Integrity: Very few (1-3)
Viability/Integrity Comments: Number of individuals found at three of the streams in Rapides Parish has been high since 1985 (average estimate is over 2,000 individuals per site) (Shively and Vermillion, 1998). In Grant Parish it was found in 60% of the total stream lengths searched (Shively, 1999). See Shively (1999) and Shively and Vermillion (1998) for more detailed information on abundance. Most populations are found in Long Branch, Bayou Clear, Loving Creek, and Little Loving Creek (USFWS, 1989k).

Overall Threat Impact: Very high - high
Overall Threat Impact Comments: The scattered occurrence of the Louisiana pearlshell in headwater streams suggests a historic range including most, if not all, of the Bayou Boeuf headwater systems, and that impoundments have eliminated populations intervening areas (USFWS, 1989k). Kincaid Reservoir impounds the uppermost headwaters of Bayou Boeuf. Inundation by beaver dams is a significant threat (the species is especially sensitive to impoundments) to the species as well and at least one population was eliminated due to beaver dam flooding (Matthews and Moseley, 1990). Habitat within the Kisatchie National Forest has been affected by sedimentation resulting from silviculture practices, road construction and maintenance, and cattle grazing under an open range policy. Sedimentation from gravel pit mining activities have also resulted in impacts to the species' habitat, particularly in the Indian Creek drainage (USFWS, 1989). Due to the high visibility of this species in shallow waters where it is often evident protruding from the substrate, it is vulnerable to collection.

Impoundments have reduced and fragmented the Louisiana Pearlshell's historic range by isolating populations. Inundation by beaver dams is a significant threat, with the small localized populations being especially vulnerable. Sedimentation from gravel mining and possibly silviculture activities is also a threat. Where clear cuts extend to the stream bank, there is increased sedimentation from erosion and scouring of the substrate resulting from increased water velocity. Removal of the canopy may also adversely affect the habitat of this species.

Short-term Trend: Decline of >70%

Long-term Trend: Decline of 70-90%
Long-term Trend Comments: The scattered occurrence of the Louisiana pearlshell in headwater streams suggests a historic range including most, if not all, of the Bayou Boeuf headwater systems, and that impoundments have eliminated populations intervening areas (USFWS, 1989k). Only one confirmed record in Arkansas has been recorded from Dorcheat Bayou (Columbia County) (Smith, 2001), but the lack of recent evidence in that state indicates it is extirpated from Arkansas.

Intrinsic Vulnerability: Unknown

Environmental Specificity: Very narrow. Specialist or community with key requirements scarce.
Environmental Specificity Comments: This species only occurs in soft water oligotrophic small creeks in a small area in Louisiana and is highly intolerant of adverse impacts from poor water quality (USFWS, 1989k).

Other NatureServe Conservation Status Information

Protection Needs: See USFWS Recovery Plan.

Distribution
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Global Range: (100-250 square km (about 40-100 square miles)) Vidrine (1993) reported this species to be rare from small streams in central Luouisiana and included such sites as Spring Creek (Bayou Cocodrie drainage), Catahoula Ranger District streams flowing into the southern end of the Red River. This species is currently restricted to two subpopulations on opposite sides of the Red River drainage in central Louisiana (Shively, 1999; Vidrine, 1993). Johnson and Brown (1998) claim the species is limited to 22 headwater streams in the Red River basin of central Louisiana. Based on museum records there are indications that it may have historically occurred throughout the headwater streams of the Bayou Boeuf drainage (USFWS, 1989k). Populations in Alabama are now ascribed to Margaritifera marrianae (Johnson, 1983).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
Endemism: endemic to a single nation

U.S. & Canada State/Province Distribution
United States AR, LA

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
LA Grant (22043), Rapides (22079)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
08 Lower Red (08040301), Little (08040304), Bayou Cocodrie (08040306), Boeuf (08050001)*, Lower Mississippi-Natchez (08060100), Bayou Teche (08080102)+, Mermentau (08080202)*
11 Loggy Bayou (11140203)*, Lower Red-Lake Iatt (11140207)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
U.S. Distribution by Watershed (based on multiple information sources) Help
Ecology & Life History
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Basic Description: An elliptically shaped freshwater mussel with a dark brown to black shell.
General Description: Shell oblong, obovate to subrhomboid, sometimes a little arcuate, subsolid to solid, inequilateral. Beaks moderately full, their sculpturesomewhat doubled. Anterior end feebly poionted below the median line and sometimes angled at the base. Surface with crude, uneven growth lines. Posterior end with more or less distinctly marked with corrugated sculpture, often divaricately plicate. Epidermis tawny-brownish or blackish. Left valve with two low, stumpy, rough pseudocardinals and two remote, feeble laterals. Right valve with one pseudocardinal and behind it a vestige of a second with one lateral. Laterals granular with traces of vertical striation. Muiscle scars impressed, the anterior rough, the posterior elliptical. Nacre whitish or lurid purplish with numerous pits (Vidrine, 1993).
Diagnostic Characteristics: See Smith (1988)
Reproduction Comments: Oviposition and spawning take place between late November and late January; with individuals gravid during winter months (Smith, 1988). Hosts include striped shiner (Luxilus chrysocephalus), redfin shiner (Lythrurus umbratilis), and golden shiner (Notemigonus crysoleucas) (Hill, 1987).
Habitat Type: Freshwater
Non-Migrant: Y
Locally Migrant: N
Long Distance Migrant: N
Mobility and Migration Comments: This species probably is rather sessile with only limited movement in the substrate. Passive downstream movement may occur when mussels are displaced from the substrate during floods. Major dispersal occurs while glochidia are encysted on their hosts.

Riverine Habitat(s): CREEK, Pool, Riffle
Special Habitat Factors: Benthic
Habitat Comments: This species is usually found in small sandy creeks with stable sand and gravel substrates in clear-flowing shallow water (Vidrine, 1993). Shively and Vermillion (1998) found mussels on "consolidated gravel outcroppings where streams cut into the base of a slope, or in sand substrate along the outside of bends in the stream or along logs in the streams." Mussel density related to water depth, substrate size, substrate compaction,a nd water velocity. Mussels rare in deep, stagnant pools with silt-covered bottoms, and more common in shallow, wide areas of streams with higher current velocitiies and in sediments with larger particle sizes. Mussel beds also more likely to occur in sections of the stream where the substrate was more stable through time (Johnson and Brown, 2000). Mussels are more common in riffles with stable substrata such as gravel than in pools (suboptimal habitat) (Bolden and Brown, 2001).
Adult Food Habits: Detritivore
Immature Food Habits: Parasitic
Phenology Comments: The maximum ages of Margaritifera hembeli, estimated from size and growth rates, ranged among sites from 45-75 years (Johnson and Brown, 1998).
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: This species was listed as endangered on February 5, 1988 (USFWS, 1988). On September 24, 1993, it was reclassified as threatened (USFWS, 1993) because of the discovery of additional populations and because the Kisatchie National Forest is actively controlling beaver populations and provides for streamside zones along the banks of perennial and intermittent streams. These streamside zones are managed for water quality and wildlife with timber harvest being limited to selective cutting for wildlife habitat improvement. A recovery plan (USFWS, 1989) was also drafted.
Population/Occurrence Delineation
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Group Name: Freshwater Mussels

Use Class: Not applicable
Minimum Criteria for an Occurrence: Occurrences are based on some evidence of historical or current presence of single or multiple specimens, including live specimens or recently dead shells (i.e., soft tissue still attached and/or nacre still glossy and iridescent without signs of external weathering or staining), at a given location with potentially recurring existence. Weathered shells constitute a historic occurrence. Evidence is derived from reliable published observation or collection data; unpublished, though documented (i.e. government or agency reports, web sites, etc.) observation or collection data; or museum specimen information.
Mapping Guidance: Based on the separation distances outlined herein, for freshwater mussels in STANDING WATER (or backwater areas of flowing water such as oxbows and sloughs), all standing water bodies with either (1) greater than 2 km linear distance of unsuitable habitat between (i.e. lotic connections), or (2) more than 10 km of apparently unoccupied though suitable habitat (including lentic shoreline, linear distance across water bodies, and lentic water bodies with proper lotic connections), are considered separate element occurrences. Only the largest standing water bodies (with 20 km linear shoreline or greater) may have greater than one element occurrence within each. Multiple collection or observation locations in one lake, for example, would only constitute multiple occurrences in the largest lakes, and only then if there was some likelihood that unsurveyed areas between collections did not contain the element.

For freshwater mussels in FLOWING WATER conditions, occurrences are separated by a distance of more than 2 stream km of unsuitable habitat, or a distance of more than 10 stream km of apparently unoccupied though suitable habitat. Standing water between occurrences is considered suitable habitat when calculating separation distance for flowing water mussel species unless dispersal barriers (see Separation Barriers) are in place.

Several mussel species in North America occur in both standing and flowing water (see Specs Notes). Calculation of separation distance and determination of separation barriers for these taxa should take into account the environment in which the element was collected. Juvenile mussels do not follow this pattern and juveniles are typically missed by most standard sampling methods (Hastie and Cosgrove, 2002; Neves and Widlak, 1987), therefore juvenile movement is not considered when calculating separation distance.

Separation Barriers: Separation barriers within standing water bodies are based solely on separation distance (see Separation Distance-suitable, below). Separation barriers between standing water bodies and within flowing water systems include lack of lotic connections, natural barriers such as upland habitat, absence of appropriate species specific fish hosts, water depth greater than 10 meters (Cvancara, 1972; Moyle and Bacon, 1969) or anthropogenic barriers to water flow such as dams or other impoundments and high waterfalls.
Separation Distance for Unsuitable Habitat: 2 km
Separation Distance for Suitable Habitat: 10 km
Alternate Separation Procedure: None
Separation Justification: Adult freshwater mussels are largely sedentary spending their entire lives very near to the place where they first successfully settled (Coker et al., 1921; Watters, 1992). Strayer (1999) demonstrated in field trials that mussels in streams occur chiefly in flow refuges, or relatively stable areas that displayed little movement of particles during flood events. Flow refuges conceivably allow relatively immobile mussels to remain in the same general location throughout their entire lives. Movement occurs with the impetus of some stimulus (nearby water disturbance, physical removal from the water such as during collection, exposure conditions during low water, seasonal temperature change or associated diurnal cycles) and during spawning. Movement is confined to either vertical movement burrowing deeper into sediments though rarely completely beneath the surface, or horizontal movement in a distinct path often away from the area of stimulus. Vertical movement is generally seasonal with rapid descent into the sediment in autumn and gradual reappearance at the surface during spring (Amyot and Downing, 1991; 1997). Horizontal movement is generally on the order of a few meters at most and is associated with day length and during times of spawning (Amyot and Downing, 1997). Such locomotion plays little, if any, part in the distribution of freshwater mussels as these limited movements are not dispersal mechanisms. Dispersal patterns are largely speculative but have been attributed to stream size and surface geology (Strayer, 1983; Strayer and Ralley, 1993; van der Schalie, 1938), utilization of flow refuges during flood stages (Strayer, 1999), and patterns of host fish distribution during spawning periods (Haag and Warren, 1998; Watters, 1992). Lee and DeAngelis (1997) modeled the dispersal of freshwater into unoccupied habitats as a traveling wave front with a velocity ranging from 0.87 to 2.47 km/year (depending on mussel life span) with increase in glochidial attachment rate to fish having no effect on wave velocity.

Nearly all mussels require a host or hosts during the parasitic larval portion of their life cycle. Hosts are usually fish, but a few exceptional species utilize amphibians as hosts (Van Snik Gray et al., 2002; Howard, 1915) or may metamorphose without a host (Allen, 1924; Barfield et al., 1998; Lefevre and Curtis, 1911; 1912). Haag and Warren (1998) found that densities of host generalist mussels (using a variety of hosts from many different families) and displaying host specialists (using a small number of hosts usually in the same family but mussel females have behavioral modifications to attract hosts to the gravid female) were independent of the densities of their hosts. Densities of non-displaying host specialist mussels (using a small number of hosts usually in the same family but without host-attracting behavior) were correlated positively with densities of their hosts. Upstream dispersal of host fish for non-displaying host specialist mussels could, theoretically, transport mussel larvae (glochidia) over long distances through unsuitable habitat, but it is unlikely that this occurs very often. D. Strayer (personal communication) suggested a distance of at least 10 km, but a greater distance between occurrences may be necessary to constitute genetic separation of populations. As such, separation distance is based on a set, though arbitrary, distance between two known points of occurrence.

Date: 18Oct2004
Author: Cordeiro, J.
Notes: Contact Jay Cordeiro (jay_cordeiro@natureserve.org) for a complete list of freshwater mussel taxa sorted by flow regime.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 19Nov2007
NatureServe Conservation Status Factors Author: Cordeiro, J. (2007); Morrison, M. (2000)
Management Information Edition Date: 19Nov2007
Management Information Edition Author: Cordeiro, J.
Element Ecology & Life History Edition Date: 27Jul2006
Element Ecology & Life History Author(s): Cordeiro, J.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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  • Bolden, S.R. and K.M. Brown. 2002. Role of stream, habitat, and density in predicting translocation success in the threatened Louisiana pearlshell, Margaritifera hembeli (Conrad). Journal of the North American Benthological Society, 21(1): 89-96.

  • Davis, G.M. and S.L.H. Fuller. 1981. Genetic relationships among recent Unionacea (Bivalvia) of North America. Malacologia, 20(2): 217-253.

  • Hill, A.M. 1987. The glochidia (larvae) of the freshwater mussel Margaritifera hembeli (Unionacea: Margaritiferidae) fish host species, morphology and period of fish host infection. M.S. Thesis, Northwestern State College of Louisiana, Natchitoches, Louisiana.

  • Howard, A.D. 1915. Some exceptional cases of breeding among the Unionidae. The Nautilus 29:4-11.

  • Huff, S.W., D. Campbell, D.L. Gustafson, C. Lydeard, C.R. Altaba, and G. Giribet. 2004. Investigations into the phylogenetic relationships of freshwater pearl mussels (Bivalvia: Margaritiferidae) based on molecular data: implications for their taxonomy and biogeography. Journal of Molluscan Studies, 70: 379-388.

  • Johnson, P.D. and K.M. Brown. 1998. Intraspecific life history variation in the threatened Louisiana pearlshell mussel, Margaritifera hembeli. Freshwater Biology, 40: 317-329.

  • Johnson, P.D. and K.M. Brown. 2000. The importance of microhabitat factors and habitat stability to the threatened Louisiana pearl shell, Margaritifera hembeli (Conrad). Canadian Journal of Zoology, 78: 1-7.

  • Johnson, R.I. 1983. Margaritifera marrianae, a new species of Unioniacea (Bivalvia: Margaritiferidae) from the Mobile-Alabama-Coosa and Escambia river systems, Alabama. Occasional Papers on Mollusks, 4(62): 299-304.

  • Lefevre, G. and W.T. Curtis. 1912. Studies on the reproduction and artificial propogation of fresh-water mussels. Bulletin of the Bureau of Fisheries 30:102-201.

  • Matthews, J.R. and C.J. Moseley (eds.). 1990. The Official World Wildlife Fund Guide to Endangered Species of North America. Volume 1. Plants, Mammals. xxiii + pp 1-560 + 33 pp. appendix + 6 pp. glossary + 16 pp. index. Volume 2. Birds, Reptiles, Amphibians, Fishes, Mussels, Crustaceans, Snails, Insects, and Arachnids. xiii + pp. 561-1180. Beacham Publications, Inc., Washington, D.C.

  • 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.

  • Shively, S.H. and W.G. Vermillion. 1998. 1998 Survey for the Louisiana pearlshell (Margaritifera marrianae) in Rapides Parish, LA. Louisiana Natural Heritage Program, Department of Wildlife and Fisheries: Baton Rouge, Louisiana. 18 pp.+ app.

  • Smith, D.G. 1976. The distribution of the Margaritiferidae: a review and new synthesis. Bulletin of the American Malacological Union, 1976: 42.

  • Smith, D.G. 1986. The stomach anatomy of some eastern North American Margaritiferidae (Unionoida: Unionacea). American Malacological Bulletin, 4(1): 13-19.

  • Smith, D.G. 1988. Notes on the biology and morphology of Margaritifera hembeli (Conrad, 1838) (Unionacea: Margaritiferidae). The Nautilus, 102(4): 159-163.

  • Smith, D.G. and W.P. Wall. 1984. The Margaritiferidae reinstated: a reply to Davis and Fuller (1981), "genetic relationships among recent Unionacea of North America." Occasional Papers on Mollusks, 4: 321-330.

  • 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.

  • Strayer, D.L. 1999a. Use of flow refuges by unionid mussels in rivers. Journal of the North American Benthological Society 18(4):468-476.

  • Strayer, D.L. and J. Ralley. 1993. Microhabitat use by an assemblage of stream-dwelling unionaceans (Bivalvia) including two rare species of Alasmidonta. Journal of the North American Benthological Society 12(3):247-258.

  • 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.

  • U.S. Fish and Wildlife Service (USFWS). 1988. Endangered and threatened wildlife and plants; final endangered status for the Louisiana pearlshell Margaritifera hembeli. Federal Register 53(24): 3567-3569.

  • U.S. Fish and Wildlife Service (USFWS). 1993. Endangered and Threatened Wildlife and Plants: Determination to Reclassify the Louisiana Pearlshell (Margaritifera hembeli) from Endangered to Threatened. Federal Register 58(184): 49935-49937.

  • Van der Schalie, H. 1938a. The naiad fauna of the Huron River in southeastern Michigan. Miscellaneous Publication of the Museum of Zoology, University of Michigan 40:7-78.

  • Watters, G.T. 1992a. Unionids, fishes, and the species-area curve. Journal of Biogeography 19:481-490.

  • Williams, J.D., M.L. Warren, Jr., K.S. Cummings, J.L. Harris, and R.J. Neves. 1993b. Conservation status of freshwater mussels of the United States and Canada. Fisheries 18(9): 6-22.

  • Ziuganov, V., A. Zotin, L. Nezlin, and V. Tretiakov. 1994. The Freshwater Pearl Mussels and Their Relationships with Salmonid Fish. VNIRO Publishing House: Moscow, Russia. 104 pp.

References for Watershed Distribution Map
  • Biological Resources Division, USGS. 1997. Database of museum records of aquatic species. Compiled by J. Williams (USGS-BRD, Gainesville, FL).

  • Shively, S.H. 1999. 1999 Survey for the Louisiana pearlshell (Margaritifera marrianae) in Grant Parish, LA. Louisiana Natural Heritage Program, Department of Wildlife and Fisheries: Baton Rouge, Louisiana. 10 pp.+ appendices.

  • Smith, D.G. 2001. Systematic and distribution of the recent Margaritiferidae. Pages 33-49 in G. Bauer and K. Wachter (eds.) Ecology and Evolution of the Freshwater Mussels Unionoida. Springer-Verlag: Berlin, Germany.

  • U.S. Fish and Wildlife Service (USFWS). 1989k. Louisiana pearlshell (Margaritifera hembeli) recovery plan. U.S. Fish and Wildlife Service: Jackson, Mississippi. 15 pp.

  • Vidrine, M.F. 1993. The Historical Distributions of Freshwater Mussels in Louisiana. Gail Q. Vidrine Collectibles: Eunice, Louisiana. xii + 225 pp. + 20 plates.

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