The dwarf wedgemussel (''Alasmidonta heterodon'') is an

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...

of freshwater

mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and Freshwater bivalve, freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other ...

, an aquatic

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

in the family Unionidae, the river mussels.

Distribution and conservation status

This is a rare species found solely in

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

's Atlantic coast streams and rivers of various sizes and moderate current. The dwarf wedge mussel's current range extends from

New Hampshire New Hampshire is a U.S. state, state in the New England region of the northeastern United States. It is bordered by Massachusetts to the south, Vermont to the west, Maine and the Gulf of Maine to the east, and the Canadian province of Quebec t ...

North Carolina North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and So ...

. The dwarf wedge mussel is federally listed as endangered and state-listed as endangered in

Connecticut Connecticut () is the southernmost state in the New England region of the Northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, New York to the west, and Long Island Sound to the south. Its cap ...

Massachusetts Massachusetts (Massachusett language, Massachusett: ''Muhsachuweesut assachusett writing systems, məhswatʃəwiːsət'' English: , ), officially the Commonwealth of Massachusetts, is the most populous U.S. state, state in the New England ...

Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...

New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...

New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...

Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...

, and

Vermont Vermont () is a state in the northeast New England region of the United States. Vermont is bordered by the states of Massachusetts to the south, New Hampshire to the east, and New York to the west, and the Canadian province of Quebec to ...

. It previously lived in

New Brunswick New Brunswick (french: Nouveau-Brunswick, , locally ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. It is the only province with both English and ...

, but it is locally extirpated in Canada since 1968.COSEWIC. 2005. Canadian Species at Risk]. Committee on the Status of Endangered Wildlife in Canada. 64 pp., page 8. The Canadian Species at Risk Act listed the Dwarf Wedge Mussel in the

List of Wildlife Species at Risk The List of Wildlife Species at Risk currently has more than 800 entries for Canadian wild life species considered vulnerable; including 363 classified as endangered species, —190 threatened species, —235 special concern, and 22 extirpated ( ...

as being extirpated in

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

Biotope

This mussel may be found in small creeks to deep rivers in stable habitats with substrates ranging from mixed sand, pebble and gravel, to clay and silty sand. In the southern portion of its range, it is often found buried under logs or root mats in shallow water (USFWS 1993), where in the northern portion of its range, it may be found in firm substrates of mixed sand, gravel or cobble, or embedded in clay banks in water depths of a few inches to greater than 20 feet (Fichtel and Smith 1995; Gabriel 1995; Gabriel 1996; Nedeau and Werle 2003; Nedeau 2004a, 2004b, 2006).

Description

The Dwarf Wedgemussel is one of 24 freshwater mussel from North America that has two lateral teeth on the right valve and only one on the left side. The dwarf wedgemussel is a small mussel, whose shell size rarely exceeds 45 mm in length and 25 mm high. The trapezoidal-shaped shells are colored brown or yellowish-olive, with reddish brown or greenish rays in young or pale specimens. The

nacre Nacre ( , ), also known as mother of pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is f ...

is bluish or silvery white, and is

iridescent Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfl ...

on the posterior.

Biology and ecology

Its reproductive cycle is typical of other freshwater mussels, requiring a host fish on which its larvae ( glochidia) parasitize and metamorphose into juvenile mussels. The dwarf wedgemussel is not a long-lived species as compared to other freshwater mussels; life expectancy is estimated at 10 to 12 years (Michaelson and Neves 1995). A number of fish species have been positively identified as hosts for the dwarf wedgemussel. Michaelson and Neves (1995) confirmed the

tessellated darter The tessellated darter (''Etheostoma olmstedi'') is a species of freshwater ray-finned fish, a darter from the subfamily Etheostomatinae, part of the family Percidae, which also contains the perches, ruffes and pikeperches. It is native to Canad ...

(''

Etheostoma olmstedi The tessellated darter (''Etheostoma olmstedi'') is a species of freshwater ray-finned fish, a darter from the subfamily Etheostomatinae, part of the family Percidae, which also contains the perches, ruffes and pikeperches. It is native to Canad ...

''), Johnny darter (''

Etheostoma nigrum The johnny darter (''Etheostoma nigrum'') is a species of freshwater ray-finned fish, a darter from the subfamily Etheostomatinae, part of the family Percidae, which also contains the perches, ruffes and pikeperches. It is native to shallow wa ...

''), and

mottled sculpin The mottled sculpin (''Cottus bairdii'') is a species of freshawater ray-finned fish belonging to the family Cottidae, the typical sculpins. This species has a wide but scattered North American distribution. As the name suggests, its coloration ...

(''Cottus bairdi'') as host fish for dwarf wedgemussels in the southern part of its range. Wicklow (''in'' New Hampshire Wildlife Action Plan 2005) confirmed the slimy sculpin (. congatus'') and juvenile and parr of the

Atlantic salmon The Atlantic salmon (''Salmo salar'') is a species of ray-finned fish in the family Salmonidae. It is the third largest of the Salmonidae, behind Siberian taimen and Pacific Chinook salmon, growing up to a meter in length. Atlantic salmon are ...

(''Salmo salar'') as host fish for dwarf wedgemussels in New Hampshire. The dwarf wedgemussel is considered to be a long-term brooder. In general, dwarf wedgemussel glochidia may be released between March and June, with peak release times varying from south to north. Michaelson and Neves (1995) documented the reproductive cycle of the dwarf wedgemussel from North Carolina and observed that this species spawns in late summer, becomes gravid in September, and releases glochidia in April. Wicklow (''in'' New Hampshire Wildlife Action Plan 2005) observed glochidia release beginning in March and continuing through June in the

Ashuelot River The Ashuelot River is a tributary of the Connecticut River, approximately long, in southwestern New Hampshire in the United States. It drains a mountainous area of , including much of the area known as the Monadnock Region. It is the longest tri ...

in New Hampshire. In a study of dwarf wedgemussel reproduction in the Mill River, Massachusetts, McLain and Ross (2005) observed that most glochidia were released in April and May. Reproductive output appears to be correlated with local population abundance. McLain and Ross (2005) documented that sites with the highest abundance of adult dwarf wedgemussels also demonstrated the highest proportion of gravid females, glochidial density, host infection, and density of juvenile mussels.

Populations

At one time, this species was recorded from 70 localities in 15 major drainages ranging from North Carolina to

, Canada. Since the species was first listed as endangered by the U.S. Fish and Wildlife Service in 1990 (55 FR 9447 9451), a number of new locations have been discovered and a number of known locations are possibly no longer extant. Based on preliminary information, the dwarf wedgemussel is currently found in 15 major drainages, comprising approximately 70 “sites” (one site may have multiple occurrences). At least 45 of these sites are based on less than five individuals or solely on spent shells. The only known occurrence in New Brunswick, Canada (Petticodiac River) appears to be historic; no live mussels or spent shells were found during a 1997 survey (Hanson 1998). The mainstem of the

Connecticut River The Connecticut River is the longest river in the New England region of the United States, flowing roughly southward for through four states. It rises 300 yards (270 m) south of the U.S. border with Quebec, Canada, and discharges at Long Island ...

in New Hampshire and

is considered to have the largest remaining dwarf wedgemussel population, consisting of three distinct stretches of sporadically occupied habitat segmented by hydroelectric dams. It is estimated that there are hundreds of thousands of dwarf wedgemussels scattered within an approximate 75-mile stretch of the Connecticut River. The Ashuelot River in New Hampshire, the Farmington River in Connecticut, and the

Neversink River The Neversink River (also called Neversink Creek in its upper course) is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed April 1, 2011 tributary of the Delaware River in southeastern Ne ...

harbor large populations, but these number in the thousands only. The remaining populations from

south to North Carolina are estimated at a few individuals to a few hundred individuals. Strayer et al. (1996) speculated that many dwarf wedgemussel populations, particularly in the southern portion of the range, may be threatened by low densities, small ranges. and linear structure (i.e., an entire population in one stream with no possibility of refuge from catastrophes or stochastic events). Low-density populations may lead to a loss of productivity due to reproductive impediments (e.g., the distance between mussels being too great) or loss of genetic variability. The Mill River in Hatfield and Whately, Massachusetts is an example of a river with a dwarf wedgemussel population patchily distributed over an approximate 16-mile stretch. The most reproductively robust patch is limited to a small stretch (< 1 mile) making it extremely vulnerable to a catastrophic event. The remainder dwarf wedgemussels are sparsely scattered and may demonstrate a reduced capability to reproduce as indicated by McLain and Ross (2005). Agricultural run-off has been identified as a significant threat to dwarf wedgemussel populations in Massachusetts,

, and North Carolina. In 2001, more than 25 dwarf wedgemussels and hundreds of other mussels (including state-listed species) were killed in the Mill River, Massachusetts, by waste run-off from a small farm. Recently, severe flooding in the Baltimore and Neversink Rivers in

and

, respectively, resulted in the destruction of occupied habitat and loss of dwarf wedgemussels. Surveys conducted at two sites on the Neversink River below a dam in Cuddebackville, New York, derived abundance estimates ranging from 60 to 500 dwarf wedgemussels per site (Cole et al. 2004) prior to 2005. Severe flooding in the spring of 2005 scoured the river channel and deposited cobble in at least one of the sites previously surveyed. Resurveys in 2005 of the two sites conducted after the flood event detected one fresh dead dwarf wedgemussel and no live mussels (Cole and White 2006). Surveys in 2006 indicated that the dwarf wedgemussel population in the Neversink River was adversely affected by flood events, although some live mussels were detected. Little riverine habitat adjacent to extant populations is protected other than by state shoreline protection regulations or local land use regulations. Development of adjacent uplands continues to be a significant and pervasive threat to southern populations. In summary, it appears that the populations in North Carolina, Virginia, and Maryland are declining as evidenced by low densities, lack of reproduction, or inability to relocate any dwarf wedgemussels in follow-up surveys. Populations in New Hampshire, Massachusetts, and Connecticut appear to be stable, while the status of populations in the

Delaware River The Delaware River is a major river in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. From the meeting of its branches in Hancock (village), New York, Hancock, New York, the river flows for along the borders of N ...

watershed affected by the recent floods of 2005 is uncertain at this time.

References

Footnotes

Bibliography

Dwarf Wedgemussel Recovery Plan: US Fish and Wildlife Service
(PDF document)
NatureServe Explorer report

* Cole, J. C., B. S. White and C. Apse. 2004. A quantitative assessment of freshwater mussels (Bivalvia:Unionidae) in the Neversink River prior to the Cuddebackville Dam removal. Report to The Nature Conservancy, Cuddebackville, New York. 16 pp. * Cole, J. and B. S. White. 2006. An assessment of freshwater mussels in the Neversink River following removal of the dam at Cuddebackville, NY and a severe spring flood event. Report to The Nature Conservancy, Cuddebackville, NY. 12 pp. * Fichtel, C. and D. G. Smith. 1995. The Freshwater Mussels of Vermont. Nongame and Natural Heritage Program, Vermont Fish and Wildlife Department. Technical Report 18. 53 pp. * Gabriel, M. 1995. Freshwater mussel distribution in the rivers and streams of Cheshire, Hillsborough, Merrimack and Rockingham, Counties, New Hampshire. Report submitted to U.S. Fish and Wildlife Service, New England Field Office and New Hampshire Fish and Game Department. 60 pp. * Gabriel, M. 1996. 1996 Monitoring of the dwarf wedgemussel (Alasmidonta heterodon) in the Ashuelot and Connecticut Rivers, New Hampshire. Report submitted to The Nature Conservancy, Eastern Regional Office, Boston, Massachusetts. 27 pp. * Hanson, M. J. 1998. March 24. Re: status of dwarf wedgemussel ersonal email Accessed March 24, 1998. * McLain, D. and M. R. Ross. 2005. Reproduction based on local patch size of Alasmidonta heterodon and dispersal by its darter host in the Mill River, Massachusetts, USA. Jour. N. Am. Benthol. Soc., 24(1):139-147. * Michaelson, D. L. and R. J. Neves. 1995. Life History and habitat of the endangered dwarf wedgemussel Alasmidonta heterodon (Bivalvia:Unionidae). Jour. N. Am. Benthol. Soc. 14:324-340. * Nedeau, E. J. 2004a. A Fourth Investigation of the Survival of Dwarf Wedgemussels (Alasmidonta heterodon) for the Relocation Project on the Connecticut River, Route 2 Stabilization Project, Lunenburg, Vermont. Unpublished report submitted to the U.S. Fish and Wildlife Service, Concord, New Hampshire. 7 pp. * Nedeau, E. J. 2004b. Quantitative survey of dwarf wedgemussel (Alasmidonta heterodon) populations downstream of the Surry Mountain Flood Control Dam on the Ashuelot River. . Unpublished report submitted to the U.S. Fish and Wildlife Service, Concord, New Hampshire. 12 pp. * Nedeau, E. 2006. Characterizing the Range and Habitat of Dwarf Wedgemussels in the “Middle Macrosite” of the Upper Connecticut River. Unpublished report submitted to the U.S. Fish and Wildlife Service, Concord, New Hampshire. 6 pp. * Nedeau, E. J. and S. Werle. 2003. Freshwater Mussels of the Ashuelot River: Keene to Hinsdale. Unpublished report submitted to the U.S. Fish and Wildlife Service, Concord, New Hampshire. 50 pp. * Strayer, D. L., S. J. Sprague and S. Claypool. 1996. A range-wide assessment of populations of the dwarf wedgemussel Alasmidonta heterodon. J. N. Am. Benthol. Soc. 15(3):308-317. * U.S. Fish and Wildlife Service. 1993. Dwarf Wedge Mussel Alasmidonta heterodon Recovery Plan. Hadley, Massachusetts. 52 pp. * Wicklow, B. 2005. in New Hampshire Wildlife Action Plan. New Hampshire Fish and Game Department, 11 Hazen Dr., Concord, NH, 03301. pp. A26-A35. {{Authority control Alasmidonta IUCN Red List vulnerable species Bivalves described in 1830 ESA endangered species Taxa named by Isaac Lea