Lasmigona subviridis - (Conrad, 1835)
Green Floater
Taxonomic Status: Accepted
Related ITIS Name(s): Lasmigona subviridis (Conrad, 1835) (TSN 80142)
Unique Identifier: ELEMENT_GLOBAL.2.107377
Element Code: IMBIV22060
Informal Taxonomy: Animals, Invertebrates - Mollusks - Freshwater Mussels
 
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Bivalvia Unionoida Unionidae Lasmigona
Genus Size: C - Small genus (6-20 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: Lasmigona subviridis
Taxonomic Comments: This taxon is recognized as a distinct species over most of its range. The only area of contention is in the drainages south of the Cape Fear basin of North Carolina. A second recognized species, Lasmigona decorata, appears here and most, if not all, older records of Lasmigona subviridis from south of the Cape Fear Basin are now assigned to L. decorata. See Clarke (1985) for a full discussion of taxonomy of this genus. West Virginia populations off the Atlantic Slope may represent another species. King, Eackles, and Hoeh (1999) found a zone of discontinuity in the genetic population structure between a group of L. subviridis inhabiting the Susquehana and Potomac rivers and more southerly distributed populations. Also, Brim Box and Williams (2000) reported L. subviridis from teh Apalachicola Basin in Georgia and Alabama, based on three records, but these Apalachicoal speicmens are slightly different conchologically (lateral teeth) from those of the southern Atlantic Coast. These specimens could rpresent an undescribed species, but it appears the population is extinct so the question may never be resolved (Williams et al., 2008).
Conservation Status
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NatureServe Status

Global Status: G3
Global Status Last Reviewed: 23Dec2011
Global Status Last Changed: 04Dec1998
Rounded Global Status: G3 - Vulnerable
Reasons: This species has recently been found more infrequently and in generally lower numbers than previously with many documented extirpated occurrences. However, this species is easier to overlook than others and might be under-sampled; and it still maintains a wide range (although there is considerable confusion as to the taxonomy of this species in the northern part of its range). Although occurrences are still widespread, decline is evident at many localities and historical extirpations have occurred in several states (Georgia, Kentucky).
Nation: United States
National Status: N3 (05May2009)

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 Alabama (SX), District of Columbia (SH), Georgia (SX), Maryland (S1), New Jersey (S1), New York (S1S2), North Carolina (S2), Pennsylvania (S2S3), Tennessee (S2), Virginia (S2), West Virginia (S2)

Other Statuses

IUCN Red List Category: LC - Least concern
American Fisheries Society Status: Threatened (01Jan1993)

NatureServe Global Conservation Status Factors

Range Extent: 20,000-200,000 square km (about 8000-80,000 square miles)
Range Extent Comments: Historically, this species was widespread in Atlantic drainages from the Cape Fear River of North Carolina north to the Hudson River system and westward to the St. Lawrence River system in New York (Clarke, 1985). The southern edge of range has been indistinct as Johnson (1970) previously reported specimens from South Carolina and North Carolina as Lasmigona subviridis which are now recognized as Lasmigona decorata (Clarke, 1985). Additionally it is known from the Interior Basin, specifically the Kanawha drainage system above Kanawha Falls in Virginia, West Virginia and North Carolina (Clarke, 1985). Note a disconuity exists in the genetic population structure between populations inhabiting the Susquehanna and Potomac Rivers and more southern populations (also reproductive isolation) (King et al., 1999). Historic 19th century records are known from Alabama Chattahoochee River near Columbus, Georgia (Mirarchi et al., 2004; Williams et al., 2008) but this different conchological variant is now extirpated in the Apalachicola basin (Brim Box and Williams, 2000). There is some question as to whether historic records from Kentucky are actually Leptodea fragilis.

Area of Occupancy: 2,501 to >12,500 4-km2 grid cells
Area of Occupancy Comments:  

Number of Occurrences: 21 - 80
Number of Occurrences Comments: Many historic occurrences are documented as extirpated, and few new occurrences being discovered. Very few sites are left in New York (Strayer and Jirka, 1997). As searches become more intense recently more populations are being found. Most occurrences are ranked as having poor to no viability with few individuals. In New York, it is extirpated in the Hudson River, Mohawk River, and is rare in the Oswego, Genesee, and Susquehanna basins (Strayer and Jirka, 1997). In New Jersey, it is historical in the middle Delaware and Raritan and still extant in Stony Brook (Cordeiro, 2003). Historical occurrences throughout much of Pennsylvania (Ortmann, 1919) have now been reduced to the upper and lower Susquehanna, Pine, Lower Juniata, and Sinnemahoning (PA NHP, pers. comm., 2007; Bogan, 1993). In Maryland, it is known from the Upper Potomac, Middle Potomac, and Washington Metro drainages (Bogan and Proch, 1995). It is known from the Upper Potomac in West Virginia (Taylor, 1985) as well as the Kanawha, New, Cascapon and Greenbrier (R. Taylor, pers. comm., 2007; Clayton et al., 2001). Surveys of the upper Greenbrier River drainage in West Virginia uncovered three localities (anonymous, 1996). In Virginia, it is largely confined to the western (along the West Virginia border) and central portions of the state and in the Holston and Clinch Rivers but in a survey of 134 sites in the New River drainage, Pinder et al. (2002) found it at 3 sites (Kimberling Creek, Bland Co.; Little River, Grayson Co.; New River, Grayson Co.; Middle and Upper New River drainages). In North Carolina, it is known from the Watauga and New River basins in the west and the Roanoke (Dan River), Tar, Neuse, and Cape Fear River basins in the east (Bogan, 2002) in Alleghany, Ashe, Durham, Edgecombe, Granville, Halifax, Johnston, Nash, Northampton, Orange, Person, Rockingham, Stokes, Wake, and Watauga Cos. (LeGrand et al., 2006). In Tennessee, it is known from the Watauga River, Johnson Co. (Parmalee and Bogan, 1998). Historical records (1967) are known from the Flint River, east of Gay, Pike, and Meriwether Cos., Georgia, but identification has not been confirmed (Athearn, 1992). In the Apalachicola Basin (ACF basin = Apalachicola, Chattahoochee, and Flint Rivers) of Alabama, Florida, and Georgia, a form variant (potential undescribed species) is historically known from only 2 records from the Chattahoochee River in Columbus, Georgia from the 1800s and a recent record from 1967 in the Flint River, Pike and Meriwether Cos. (see Athearn, 1992), but no specimens were found in a recent survey of 324 sites in the basin (Brim Box and Williams, 2000; Williams et al., 2008).

Population Size: Unknown
Population Size Comments: Very few sites are known to contain large numbers of live individuals, most occurrences ares based on findings of 1-5 live individuals. The best site in New York is 22 individuals found in 1.5 hours of searching (Strayer and Jirka, 1997).

Number of Occurrences with Good Viability/Integrity: Very few to few (1-12)
Viability/Integrity Comments: Very few sites are known to contain large numbers of live individuals, most occurrences ares based on findings of 1-5 live individuals. The best site in New York is 22 individuals found in 1.5 hours of searching (Strayer and Jirka, 1997).

Overall Threat Impact: High
Overall Threat Impact Comments: Habitat likely still common, but microhabitat factors such as reduced transport of silt and pollutants away from the microhabitat may be causing decline. Also, introduced Corbicula fluminea (Asian clam), Dreissena polymorpha (zebra mussel) is a threat. This species is more tolerant of less than ideal conditions when compared to Alasmidonta varicosa or Alasmidonta heterodon (Rita Villella pers. comm. 1998).

Short-term Trend: Decline of 10-30%
Short-term Trend Comments: Many historic occurrences are documented as extirpated, and few new occurrences being discovered. Very few sites are left in New York (Strayer and Jirka, 1997). As searches become more intense recently more populations are being found. Most occurrences are ranked as having poor to no viability with few individuals. In 1919 Ortmann indicated that this mussel was erratic in distribution but abundant when present. Few large populations remain and there has been a sharp decline in numbers where present (e.g., North Fork Shenandoah River) and is extant at very few historic occurrences. Good populations, such as the West fork Greenbriar either shift or are lost after major flood events. Populations of this species were probably never very good. Historical records (1967) are known from the Flint River, east of Gay, Pike, and Meriwether Cos., Georgia (Athearn, 1992). Although once widespread and common in the Susquehanna River drainage in New York, populations have declined in recent years, probably due to pollution (Strayer and Jirka, 1997).

Long-term Trend: Decline of 10-50%
Long-term Trend Comments: Historic 19th century records are known from Alabama Chattahoochee River near Columbus, Georgia (Mirarchi et al., 2004; Williams et al., 2008) but this different conchological variant is now extirpated in the Apalachicola basin in Alabama and Georgia (Brim Box and Williams, 2000). In Kentucky, it formerly occurred in Tygarts Creek (Greenup Co.) only (Cicerello and Schuster, 2003; Zeto, 1980)) but there is some question as to whether this is actually Leptodea fragilis. In New York, it is extirpated in the Hudson River, Mohawk River, and is rare in the Oswego, Genesee, and Susquehanna basins (Strayer and Jirka, 1997).

Environmental Specificity: Moderate. Generalist or community with some key requirements scarce.
Environmental Specificity Comments: Typical habitat would seem to indicate some hardiness, as does previous colonization of canals; however, has apparently become scarce and difficult to find. Because it is hermaphroditic, it can survive well with fewer individuals. It prefers quiet, clean water conditions in streams and rivers.

Other NatureServe Conservation Status Information

Inventory Needs: Spent shells have short life. Might miss this species using general mussel survey methods. Interior basin needs most effort. [need to incorporate information from Larry Master's 1993 report].

Protection Needs: Protect water quality. Note a disconuity exists in the genetic population structure between populations inhabiting the Susquehanna and Potomac Rivers and more southern populations (also reproductive isolation) (King et al., 1999), so manage separately.

Distribution
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Global Range: (20,000-200,000 square km (about 8000-80,000 square miles)) Historically, this species was widespread in Atlantic drainages from the Cape Fear River of North Carolina north to the Hudson River system and westward to the St. Lawrence River system in New York (Clarke, 1985). The southern edge of range has been indistinct as Johnson (1970) previously reported specimens from South Carolina and North Carolina as Lasmigona subviridis which are now recognized as Lasmigona decorata (Clarke, 1985). Additionally it is known from the Interior Basin, specifically the Kanawha drainage system above Kanawha Falls in Virginia, West Virginia and North Carolina (Clarke, 1985). Note a disconuity exists in the genetic population structure between populations inhabiting the Susquehanna and Potomac Rivers and more southern populations (also reproductive isolation) (King et al., 1999). Historic 19th century records are known from Alabama Chattahoochee River near Columbus, Georgia (Mirarchi et al., 2004; Williams et al., 2008) but this different conchological variant is now extirpated in the Apalachicola basin (Brim Box and Williams, 2000). There is some question as to whether historic records from Kentucky are actually Leptodea fragilis.

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 ALextirpated, DC, GAextirpated, MD, NC, NJ, NY, PA, TN, VA, WV

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
GA Meriwether (13199)*, Pike (13231)*
MD Allegany (24001), Frederick (24021), Montgomery (24031), Washington (24043)
NC Alleghany (37005), Ashe (37009), Durham (37063), Edgecombe (37065), Franklin (37069), Granville (37077), Halifax (37083), Johnston (37101), Montgomery (37123), Nash (37127), Northampton (37131), Orange (37135), Person (37145), Pitt (37147), Randolph (37151), Rockingham (37157), Stokes (37169), Wake (37183), Watauga (37189)
NJ Bergen (34003)*, Essex (34013)*, Hudson (34017)*, Mercer (34021), Middlesex (34023)*, Somerset (34035)*, Union (34039)*, Warren (34041)*
NY Allegany (36003), Broome (36007), Cayuga (36011), Chemung (36015), Chenango (36017), Cortland (36023), Delaware (36025), Livingston (36051), Monroe (36055), Otsego (36077), Schuyler (36097)*, Steuben (36101), Tioga (36107)
PA Bedford (42009)*, Blair (42013)*, Bradford (42015), Cambria (42021)*, Cameron (42023), Centre (42027), Chester (42029)*, Clinton (42035)*, Columbia (42037), Cumberland (42041), Dauphin (42043), Fulton (42057)*, Huntingdon (42061), Indiana (42063)*, Juniata (42067), Lancaster (42071), Northumberland (42097), Philadelphia (42101)*, Tioga (42117), Wyoming (42131), York (42133)
VA Albemarle (51003), Amelia (51007)*, Amherst (51009), Appomattox (51011), Bath (51017), Bland (51021), Brunswick (51025), Buckingham (51029), Buena Vista (City) (51530)*, Charlotte (51037), Chesterfield (51041)*, Clarke (51043)*, Colonial Heights (City) (51570)*, Culpeper (51047), Cumberland (51049), Dinwiddie (51053)*, Emporia (City) (51595), Fauquier (51061), Floyd (51063)*, Fluvanna (51065), Frederick (51069)*, Giles (51071)*, Goochland (51075), Grayson (51077), Halifax (51083), Hanover (51085)*, Henry (51089), King William (51101)*, Loudoun (51107), Louisa (51109)*, Lunenburg (51111), Lynchburg (City) (51680)*, Madison (51113), Mecklenburg (51117), Montgomery (51121)*, Nelson (51125), Nottoway (51135), Orange (51137), Patrick (51141), Petersburg (City) (51730)*, Powhatan (51145), Prince Edward (51147)*, Pulaski (51155)*, Rappahannock (51157), Rockbridge (51163)*, Shenandoah (51171), Spotsylvania (51177)*, Warren (51187)*, Wythe (51197)*
WV Fayette (54019), Hampshire (54027), Pocahontas (54075), Raleigh (54081)*, Summers (54089)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
02 Mohawk (02020004)*, Middle Hudson (02020006)*, Lower Hudson (02030101)*, Hackensack-Passaic (02030103)+*, Sandy Hook-Staten Island (02030104)+*, Raritan (02030105)+, Middle Delaware-Mongaup-Brodhead (02040104)+*, Middle Delaware-Musconetcong (02040105)+*, Crosswicks-Neshaminy (02040201)+*, Schuylkill (02040203)+*, Upper Susquehanna (02050101)+, Chenango (02050102)+, Owego-Wappasening (02050103)+, Tioga (02050104)+, Chemung (02050105)+, Upper Susquehanna-Tunkhannock (02050106)+, Upper Susquehanna-Lackawanna (02050107)+, Upper West Branch Susquehanna (02050201)+, Sinnemahoning (02050202)+, Bald Eagle (02050204)+, Pine (02050205)+, Lower Susquehanna-Penns (02050301)+, Upper Juniata (02050302)+*, Raystown (02050303)+*, Lower Juniata (02050304)+, Lower Susquehanna-Swatara (02050305)+, Lower Susquehanna (02050306)+, South Branch Potomac (02070001), North Branch Potomac (02070002), Cacapon-Town (02070003)+, Conococheague-Opequon (02070004)+, North Fork Shenandoah (02070006)+, Shenandoah (02070007)+, Middle Potomac-Catoctin (02070008)+, Monocacy (02070009)+, Middle Potomac-Anacostia-Occoquan (02070010), Rapidan-Upper Rappahannock (02080103)+, Lower Rappahannock (02080104), Pamunkey (02080106)+, Upper James (02080201)+, Maury (02080202)+*, Middle James-Buffalo (02080203)+, Rivanna (02080204)+, Middle James-Willis (02080205)+, Appomattox (02080207)+, Oxon Creek (02140204)+*, Anacostia River (02140205)+*
03 Middle Roanoke (03010102)+, Upper Dan (03010103)+, Lower Dan (03010104)+, Lower Roanoke (03010107)+, Nottoway (03010201)+, Meheriin (03010204)+, Upper Tar (03020101)+, Lower Tar (03020103)+, Upper Neuse (03020201)+, Contentnea (03020203)*, Upper Cape Fear (03030004)*, Lower Yadkin (03040103)+, Upper Pee Dee (03040104)+, Upper Chattahoochee (03130001)*, Middle Chattahoochee-Lake Harding (03130002)*, Middle Chattahoochee-Walter F. George Reservoir (03130003)*, Upper Flint (03130005)+*
04 Upper Genesee (04130002)+, Lower Genesee (04130003)+, Irondequoit-Ninemile (04140101)*, Seneca (04140201)+, Oneida (04140202)*
05 Upper New (05050001)+, Middle New (05050002)+, Greenbrier (05050003)+, Lower New (05050004)+, Upper Kanawha (05050006)+, Little Scioto-Tygarts (05090103)*
06 Watauga (06010103)+
+ 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: Freshwater mussel
General Description: Shell subovate to ovate, narrower in front and higher behind. Shell unsculptured. Anterior margin rounded. Ventral margin slightly convex to centrally flattened. Posterior margin sharply rounded, subacute, or somewhat biangulate below and obliquely flattened above, and dorsal margin broadly sinuate to gently convex throughout. Dorsal margin sometimes forms a winglike angle with posterior margin. Beaks, located in the anterior third of the shell, project little above hinge line (Clarke, 1985). Posterior ridge rounded, sometimes obscurely double and subangular (Clarke, 1985). Shell not compressed nor inflated. Periostracum pale yellowish or brownish with numerous narrow or wide green and blackish rays. Rays are particularly conspicuous in juveniles (Clarke, 1985). Shell is smooth, with slightly raised, darkened annulli. Teeth well-developed but small and delicate. Possesses lammellar or serrate pseudocardinal teeth oriented nearly parallel to hinge line. Left valve has 2 pseudocardinals and right valve has one. Lateral teeth narrow, sharp and of moderate length. Two lateral teeth in the left valve and one in the right valve; sometimes the lateral teeth are incomplete or indistinct (Clarke, 1985). A rudimentary interdental projection, often obscure, exists in the left valve. Shell moderately thin, with nacre white anteriorly, and posteriorly iridescent and bluish or greenish white. Nacre with blotches of dull greenish or yellowish color. From Clarke (1985):" Mantle yellowish white at the marginal muscle band, near the adductor muscles and over the diaphragm; translucent centrally and above the diaphragm. Foot orange, visceral mass yellowish white, and adductor muscles pale yellowish brown. ... Mantle with a narrow band of dark brown pigment along the margin only near the incurrent and anal openings... Outer demibranch pale orange... Inner demibranch also pale orange...". Ortmann (1912) described the species as being hermaphroditic with female gill structure occurring in the outer demibranchs of all specimens. An extensive description and illustrations of the species are available in Clarke (1985).
Diagnostic Characteristics: Yellow-to-green-to-brown periostracum, green rays, orange foot and gills, fine and complete dentition, rudimentary interdental projection, and lammellar pseudocardinals parallel to hinge identify this species. This character set is not shared by any other similarly appearing species. Kitchel (1991) states ALASMIDONTA HETERODON may be confused with this species, except A. HETERODON has a more truncate posterior margin and reversed hinge teeth. L. DECORATA may be confused with L. SUBVIRIDIS in southern North Carolina and South Carolina portion of range. Reports of L. SUBVIRIDIS in the Atlantic drainages south of the Cape Fear basin are few and likely represent L. DECORATA (Kerfel, 1990). L. DECORATA is a larger and heavier-shelled species found only south of the Cape Fear Basin; however, refer to Clarke (1985) for how to differentiate these species.
Reproduction Comments: Ortmann (1919) reported that it broods eggs/glochidia from August to June and it is therefore a long term brooder. There is recent evidence that juveniles of this species can metamorphose without a host within the marsupia of the adult female (Barfield and Watters, 1998; Lellis and King, 1998). In a survey of the New River Drainage in Virginia, Pinder et al. (2002) found this species to be gravid in August 1998.
Ecology Comments: No definitive studies. Mussel literature consists primarily of taxonomy, systematics, distribution, and life history of the taxa. No ecological studies of this species exist. It appears to be a species negatively affected by eutrophication and siltation.
Habitat Type: Freshwater
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: N
Mobility and Migration Comments: Adults are essentially sessile. Passive movement downstream may occur. Dispersal via glochidia encysted in fish.
Riverine Habitat(s): CREEK, Low gradient, MEDIUM RIVER, Moderate gradient, Pool
Special Habitat Factors: Benthic
Habitat Comments: This is considered to be a species of quiet waters, Ortmann (1919) stated, "it avoids the larger rivers and prefers smaller streams... it is averse to very strong current, and prefers the quiet parts, pools and eddies with gravelly and sandy bottoms". Clarke (1985) concurred with this description of its habitat preference. often found in small creeks and large rivers and sometimes canals. This species is intolerant of strong currents and occurs in pools and other calm water areas (Strayer and Jirka, 1997). Preferred substrate is gravel and sand in water depths of one to four feet. This species is more likely to be found in hydrologically stable streams, not those prone to flooding and drying. Good water quality is also important.
Adult Food Habits: Detritivore
Immature Food Habits: Parasitic
Food Comments: Glochidia (larval form) of freshwater mussels typically parasitic on fish. Host specificity varies among species; host(s) unidentified for LASMIGONA SUBVIRIDIS. Adult mussels are filter feeders. General literature has assumed that plankton constitute majority of food. Recent studies indicate that detritus is the primary energy source (James, 1987).
Phenology Comments: See GREPROCOM. Little has been reported regarding phenology for mussels except for period of brooding of eggs/glochidia.
Length: 4.5 centimeters
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: Determine population status and trends of local occurrences. Element occurrences that are A rank or represent best known occurrences in a given state should be monitored biannually as resources allow. Fish host(s) need to be determined. Documentation of differences between extirpated and extant element occurrences should be performed as possible to determine causes of extirpation.
Restoration Potential: Previously this species was known to occur in canals (Ortmann, 1919), therefore there appears to be some ecological tolerance for impacted or artificial environments and some ability to colonize. The alteration of water quality and the benthic microhabitats may be the overriding factors in determining its decline and or absence. Greater knowledge of tolerance in impacted environments and of competitive interactions with introduced bivalves is needed before active restoration is undertaken.
Preserve Selection & Design Considerations: Elimination of impacts to water quality is the main consideration. This includes the provision for sufficient buffers to prevent siltation, eutrophication, and toxic runoff into waters in which there is an element occurrence. For a relatively large watershed, this is possibly unfeasible; however, local protection can be significant. Protection from take could be a significant benefit of a preserve. A significant consideration is the ability to protect the site from colonization by zebra mussel, DREISSENA POLYMORPHA.
Management Requirements: Maintenance of water quality, including the reduction of siltation, pollution, and eutrophication. The host fish species must be maintained within the element occurrence for successful reproduction, unless L. SUBVIRIDIS is identified as facultatively not requiring a host. Transplantation can be done successfully for adults; however, the long term fate of such transplanted populations is uncertain. See the General Freshwater Mussel ESA, Fuller (1974), or Havlik and Marking (1987) for additional information on pollutants requiring control. Note a disconuity exists in the genetic population structure between populations inhabiting the Susquehanna and Potomac Rivers and more southern populations (also reproductive isolation) (King et al., 1999).

Monitoring Requirements: Monitoring requires determination of the density or relative density of individuals and the presence of young cohorts. For accurately determining the presence of mussels, waterscoping is required and snorkeling is recommended. Populations should be monitored either with density measures such as quadrat sampling or by recording the number of individuals found along a transect or within a specific time interval. Sampling effort to find rare mussels is frequently difficult to quantify; however, Kovalak et. al.(1986) provides a useful review of the topic and guidance on the issue. In general, it will be best to concentrate effort on the known habitats of this species. Monitoring is best accomplished during periods of low flow, typically in summer. Unusual drought or water level drops should be taken advantage of to reach areas typically not accessible. Also, a mussel population may have a significant portion of the population in a temporarily endobenthic (buried) state not visible from the surface (Amyot and Downing, 1991).

To avoid excessive disturbance from annual monitoring, monitoring programs may require only biannual visits. It is extremely important that live mussels handled during monitoring are appropriately replaced in the substrate. Failing to replace mussels into the substrate or placing them in an improper orientation can be fatal. Proper orientation requires that the anterior end be in the substrate. It is typically best to avoid handling mussels when they are at the end of the gravid period and ready to discharge glochidia. When fish host(s) are reported, monitoring should include these fish(es) in some manner.

Management Research Needs: Research into the impacts of siltation, pollution, and eutrophication are required. Habitat requirements and interaction with host habitat requirements are needed. Effects of exotic bivalves on native mussels needs research as does control measures for the exotics.

Glochidial host should be identified; however, the broad range indicates a common host species or a number of hosts are used.

Ongoing research into the ecology of the DREISSENA POLYMORPHA should be examined as this species has been predicted to exhibit thermal tolerance; it can potentially invade the entirety of the range of LASMIGONA SUBVIRIDIS (Strayer, 1990). DREISSENA POLYMORPHA appears to be excluded from streams under 10 meters in width (Strayer, 1990).

Biological Research Needs: Fish host unidentified. Taxonomic analysis of West Virginia populations off Atlantic Slope.
Additional topics: Hermaphrodism may or may not have an immediate bearing on stewardship. Future research is justified into the nature of hermaphrodism, such as whether it is simultaneous or sequential, both within and between years, and whether self-fertilization is possible.
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: 23Dec2011
NatureServe Conservation Status Factors Author: Cordeiro, J. (2011); Stevenson, P. [1992 edition]; Motivans, K. (1998)
Management Information Edition Date: 23Mar1992
Management Information Edition Author: Stevenson, Phil
Element Ecology & Life History Edition Date: 23Dec2011
Element Ecology & Life History Author(s): Cordeiro, J. (2011); STEVENSON, P. (1994)

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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