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Epioblasma torulosa

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA MOLLUSCA BIVALVIA UNIONOIDA UNIONIDAE

Scientific Name: Epioblasma torulosa
Species Authority: (Rafinesque, 1820)
Infra-specific Taxa Assessed:
Common Name(s):
English Tubercled Blossom, Green-blossom Pearly Mussel, Green-blossom Naiad, Green Riffle Shell, Green-blossom
Synonym(s):
Dysnomia torulosa (Rafinesque, 1820)
Dysnomia torulosa subspecies gubernaculum Reeve, 1865
Plagiola torulosa (Rafinesque, 1820)
Taxonomic Notes: This species is comprised of several recognized forms (torulosa, gubernaculum, rangiana, and cincinnatiensis), but it is not clear whether these forms represent ecophenotypic variation, true subspecies, or a species complex. The entire species group exhibits considerable ecophenotypic variation. Epioblasma was formerly placed in the genera Unio, Truncilla, and Dysnomia (Johnson 1978).

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: Critically Endangered A2ace ver 3.1
Year Published: 2012
Date Assessed: 2012-06-07
Assessor(s): Cummings, K. & Cordeiro, J.
Reviewer(s): Bohm, M., Seddon, M. & Collen, B.
Contributor(s): Richman, N., Dyer, E., Soulsby, A.-M., Whitton, F., Kasthala, G., McGuinness, S., Milligan, HT, De Silva, R., Herdson, R., Thorley, J., McMillan, K., Collins, A., Duncan, C. & Offord, S.
Justification:
Epioblasma torulosa has been assessed as Critically Endangered under criterion A2ace, as the species has experienced a greater than 95% range reduction which is likely to equate to a population decline of at least 80%. All subspecies are thought to be extirpated except for Epioblasma torulosa rangiana which is extant in short stretches of eight to ten rivers, with locations being largely disjunct, small, and peripheral.

Geographic Range [top]

Range Description: This species was historically found throughout the Tennessee River system (USFWS 1985). It was probably rare in the Cumberland River, and was also reported from the Ohio, Wabash, Kentucky, Scioto (Ohio) and Kanawha (West Virginia) Rivers (USFWS 1985). It was probably widespread in the larger rivers of the eastern United States and southern Ontario, Canada (USFWS 1985). Currently extant populations of this species (Epioblasma torulosa rangiana) exist within the Allegheny River, Western Pennsylvania, and Southern Ontario, Canada (K. Cummings pers. comm. 2010).
Its extent of occurrence is estimated as around 60,000 km2, although this does encompass large areas where the presence of the species is uncertain. NatureServe (2009) estimates the range extent of this species closer to 1,000-5,000 km2. Its area of occupancy is probably much smaller than this, and anywhere between 100 to 2,000 km2, thus falling within the threshold for threatened categories under criterion B.
Countries:
Native:
Canada (Ontario); United States (Ohio - Regionally Extinct, Pennsylvania, West Virginia - Regionally Extinct)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Epioblasma torulosa gubernaculum:
This subspecies is probably extinct with the last population known from the upper Clinch River above the backwater impoundment of Norris Reservoir and the last live specimens collected in 1983 and 1984 in Scott Co., Virginia (USFWS 1984).

Epioblasma torulosa rangiana
:
Epioblasma torulosa rangiana, the only remaining extant subspecies, was formerly widespread in the Ohio River basin (including Ohio River system in Ohio River at Cincinnati, Little Miami, Scioto, Muskingham, and Olentangy Rivers, and Big Darby Creek- a tributary of the Scioto River; Beaver River in Ohio and Pennsylvania; Lake Erie drainage in Fish Creek, and Kanawha River, West Virginia; Wabash River and tributaries-Tippecanoe River and the Eel, Blue, and White Rivers) (Parmalee and Bogan 1998) as well as having been collected historically from the Allegheny River drainage in Pennsylvania above Pittsburgh and from the West Fork River (Ortmann 1913), a tributary of the Monongahela River, Harrison Co., West Virginia (Parmalee and Bogan 1998, USFWS 1994). This subspecies now exists in eight to ten isolated populations, most of which are small and peripheral and with little signs of reproduction. It is known from the Kentucky, Licking, and Green River drainages in Kentucky (Johnson 1978), but is likely only still extant in the Upper Green. In the Maumee River drainage, it was last seen in Fish Creek (St. Joseph drainage) in Ohio and Indiana, where live individuals were very rare (Watters 1995, Grabarkiewicz and Crail 2008). It was recently found in Conewango Creek near Warren, Warren Co., Pennsylvania, where it was previously thought to be extirpated (Evans and Smith 2005). It also occurs in the Allegheny River, Pennsylvania (Jones 2004). The subspecies occurs in Muddy Creek (French Creek drainage) in the Erie NWR in Crawford Co., Pennsylvania (Mohler et al. 2006) and elsewhere in the French Creek drainage. Weathered shells are reported from the Tippecanoe River (shell only- Cummings and Berlocher 1990) and Sugar Creek (east fork White River drainage) in central Indiana (Harmon 1992) as well as throughout most central Indiana drainages. However, no living specimens are known recently (USFWS 1994) and Fisher (2006) lists it as extirpated from the Wabash drainage. As such, it is probably extirpated from the rest of Indiana except possibly the Tippecanoe drainage where it might still be hanging on (USFWS 1994). Specimens from the Black River (St. Clair drainage), Michigan, were relocated to the Detroit River in 1992 (Trdan and Hoeh 1993). It is historically known from the Clinton River drainage in Michigan (Strayer 1980). In Canada, it historically occurred in the Cedar River and currently occurs in the Sydenham River in the Northern Lake Erie drainage (Metcalfe-Smith et al. 2003) and also the Ausable River in the Eastern Lake Huron drainage (Staton et al. 2000).

Epioblasma torulosa torulosa:
This species is now globally extinct. This form inhabited the Tennessee River from Knox Co., Tennessee, to Muscle Shoals in northern Alabama, and downstream probably to the Ohio River and was also found in the Elk and Paint Rock Rivers in northern Alabama (Parmalee and Bogan 1998). However, it has not been reported since the Tennessee River was impounded (Mirarchi 2004). One specimen was collected in 1969 from the Kanawha River in West Virginia, but subsequent surveys revealed no other evidence of a population and no prior records are known from that river (USFWS 1985).

The only populations of the northern riffleshell, Epioblasma torulosa rangiana (the only extant subspecies), with evidence of recruitment are two populations in Pennsylvania and the Sydenham River population in Ontario (Staton et al. 2000). However, due to problems obtaining a unbiased and complete sample, abundance in mussels is always difficult to estimate, and no estimates of population size or abundance have been made for this species. Epioblasma torulosa rangiana has experienced more than a 95% range reduction (USFWS 1993, 1994, Staton et al. 2000). The other two subspecies, Epioblasma torulosa gubernaculum and Epioblasma torulosa torulosa have declined to extinction (USFWS 1984, 1993, 1994).

The northern riffleshell was listed as a federally endangered species in February of 1993. It was also considered to be Endangered by the freshwater mussel subcommittee of the endangered species committee of the American Fisheries Society (Williams et al. 1993). In the Midwest, the northern riffleshell was widely distributed and relatively common in some of the headwater streams in the Wabash and Ohio river drainages. It is Endangered in Indiana, Michigan, and Ohio, and Extirpated in Illinois. See Staton et al. (2000) for trend information.
Overall, the species is thought to have undergone range declines of around 95% (NatureServe 2009).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Although this species has been collected from water to about six feet, there is little doubt that it is primarily a riffle species of sand/gravel (Ortmann 1919, Parmalee 1967, Johnson 1978, Bogan and Parmalee 1983). Like most members of the genus, it appears to require swiftly moving water, perhaps linked to high oxygen concentrations, in order to survive. This is a species of riffle areas of large rivers which have been all but eliminated by impoundment and dredging for barge canals (Stansbery 1970, 1971).
Although Haag and Rypel (2010) only report a maximum age of nine years for this species, it is suspected to live for at least up to 50 years (USFWS 2012). Conservatively assuming a first age of maturity of between 2-9 years (Haag and Staton 2003), generation length (estimated as the average age of a parent in the population) is estimated as around 28 years, with three generations spanning around 84 years. Because of the long lifespan and resulting generation length of this species, it is highly likely that the majority of the observed declines have taken place within the past three generations.
Systems: Freshwater

Use and Trade [top]

Use and Trade: This species is not utilized.

Threats [top]

Major Threat(s): Members of this genus seem to be particularly sensitive to impoundments; most species are riffle/run inhabitants and cannot tolerate other habitats. Impoundment by the Norris Reservoir of the Clinch River in Tennessee has resulted in the extirpation of the majority of species below the dam (Ahlstedt 1984). The construction of the Wilson Dam on the Tennessee River has eliminated 20 of the original 22 Cumberlandian naiad species (Stansbery 1971). Plans to impound the Duck River in Tennessee where Athearn found Epioblasma torulosa torulosa (Bogan and Parmalee 1983) have been halted (Eddlemon and Tolbert 1983). The existing populations are predominately in mountainous areas with minimal agriculture bounding the rivers. These areas are impacted by quarry washings and fly ash runoff. USFWS (1994) lists the following reasons for decline: siltation, impoundment, instream sand and gravel mining, pollutants, and invasive species.

Epioblasma torulosa gubernaculum:
The recovery plan (USFWS, 1984) listed the following reasons for the decline of this subspecies: impoundment (for flood control, navigation, hydroelectric power, recreation), siltation (from strip mining, coal washing, dredging, farming, logging, road construction), and pollution (municipal, agricultural, industrial).

This subspecies was extremely sensitive to water quality and disturbance.

Epioblasma torulosa rangiana:
Members of the genus Epioblasma seem to be particularly sensitive to impoundment; most species are riffle/run inhabitants and cannot tolerate other habitats. Impoundment of the Clinch River in Tennessee by the Norris Reservoir has resulted in the extirpation of the majority of species below the dam (Ahlstedt 1984). The construction of the Wilson Dam on the Tennessee River has eliminated 20 of the original 22 Cumberlandian naiad species (Stansbery 1971). Smith (1971) ranked the causes of extirpation or declines in fish species as follows: siltation, drainage of bottomland lakes, swamps, and prairie marshes, desiccation during drought, species introductions, pollution, impoundments, and increased water temperatures. All of these factors render habitats unsuitable, cause extirpations, and lead to the isolation of populations thereby increasing their vulnerability to extirpation for many aquatic species (including mussels) throughout North America. Zebra mussels Dreissena polymorpha have destroyed mussel populations in the Great Lakes and significantly reduced mussels in many of the large rivers of eastern North America and has the potential to severely threaten and other populations especially if it makes its way into smaller streams. Pollution through point (industrial and residential discharge) and non-point (siltation, herbicide and fertilizer run-off) sources is perhaps the greatest on-going threat to this species and most freshwater mussels. Lowered dissolved oxygen content and elevated ammonia levels (frequently associated with agricultural runoff and sewage discharge) have been shown to be lethal to some species of freshwater naiads (Horne and McIntosh 1979). Residential, mineral and industrial development also pose a significant threat. Destruction of habitat through stream channelization and maintenance and the construction of dams although slowed in recent years is still a threat in some areas. Impoundments reduce currents that are necessary for the most basic physiological activities such as feeding, waste removal and reproduction. In addition, reduced water flow typically results in a reduction in water oxygen levels and a settling out of suspended solids (silt, etc.), both of which are detrimental. Dredging of streams has an immediate effect on existing populations by physically removing and destroying individuals. Dredging also affects the long-term recolonization abilities by destroying much of the potential habitat, making the substrates and flow rates uniform throughout the system. Rotenone, a toxin used to kill fish in bodies of water for increased sport fishery quality, has been shown to be lethal to mussels as well (Heard 1979). Natural predators include raccoons, otter, mink, muskrats, turtles and some birds, which feed heavily upon freshwater mussels (Simpson 1899, Boepple and Coker 1912, Evermann and Clark 1918, Coker et al. 1921, Parmalee 1967, Snyder and Snyder 1969). Domestic animals such as hogs can root mussel beds to pieces (Meek and Clark 1912). Fishes, particularly catfish, Ictalurus spp. and Amierus spp. and freshwater drum, Aplodinotus grunniens also consume large numbers of unionids. USFWS (1994) lists the following reasons for decline: siltation, impoundment, instream sand and gravel mining, pollutants, and invasive species.

Due to slow growth and relative immobility, establishment of sustainable, viable populations requires decades of immigration and recruitment, even where suitable habitat exists (Neves 1993). Mussel recruitment is typically low and sporadic, with population stability and viability maintained by numerous slow-growing cohorts and occasional good year classes (Neves and Widlak 1987).
The decline in the overall range of this species suggests that it is not tolerant of poor water quality. Individuals are sensitive to pollution, siltation, habitat perturbation, inundation, and loss of glochidial hosts.

Epioblasma torulosa torulosa:

This subspecies was formerly known, with few exceptions, from riffles and shoals of the largest rivers. Possibly the single greatest factor that contributed to its demise is the alteration and destruction of stream habitat due to impounements for flood control, navigation, hydroelectric power production, and recreation. Siltation is another factor that has affected these mussels. Increased silt transport was caused by strip mining, coal washing, dredging, farming, logging, and road construction. Large river species of Epioblasma tend to be particularly sensitive to siltation, requiring clean, flowing water over stable, silt-free rubble, gravel, and sand shoals. Pollution has also impacted these mussel populations. A combination of toxic wastes, gravel dredging, and increased fertilizer and pesticide use is implicated (USFWS 1985).

The decline in the overall range of this species suggests that it is not tolerant of poor water quality. Sensitive to pollution, siltation, habitat perturbation, inundation, and loss of glochidial hosts. Large river species of Epioblasma tend to be particularly sensitive to siltation, requiring clean, flowing water over stable, silt-free rubble, gravel, and sand shoals.

Conservation Actions [top]

Conservation Actions: A portion of the population in Big Darby Creek is on property owned by the Nature Conservancy. Other populations are on property that has a watershed management plan (Fish Creek in Indiana, Michigan, and Ohio) or is the subject of local conservation groups (Big Darby Creek system, Ohio; portions of the Tippecanoe River, Indiana; French Creek, Pennsylvania). Epioblasma torulosa rangiana occurs in Muddy Creek (French Creek drainage) in the Erie NWR in Crawford Co., Pennsylvania (Mohler et al. 2006).  
Epioblasma torulosa gubernaculum:
This subspecies was listed as federally endangered in the U.S. in 1976 and a recovery plan created (USFWS 1984).

Epioblasma torulosa rangiana
:
This subspecies was listed as federally endangered in the U.S. in 1993 and a recovery plan created (USFWS 1994).

Epioblasma torulosa torulosa:
This subspecies was listed as federally endangered in the U.S. In 1976 and a recovery plan created (USFWS 1985).

Williams et al. (2010) lists this species as endangered according to the American Fisheries Society (AFS) assessment. Additional research benefitting our knowledge and ability to safeguard this species has been suggested (especially, population monitoring and population and ecology research).

Citation: Cummings, K. & Cordeiro, J. 2012. Epioblasma torulosa. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 28 July 2014.
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