Eastern Pearlshell AMNH

Eastern Pearlshell
AMNH

Class
Bivalvia (Bivalves)
Family
Margaritiferidae (Pearl Mussels)
State Protection
Not Listed
Not listed or protected by New York State.
Federal Protection
Not Listed
State Conservation Status Rank
S2
Imperiled in New York - Very vulnerable to disappearing from New York due to rarity or other factors; typically 6 to 20 populations or locations in New York, very few individuals, very restricted range, few remaining acres (or miles of stream), and/or steep declines.
Global Conservation Status Rank
G4
Apparently Secure globally - Uncommon in the world but not rare; usually widespread, but may be rare in some parts of its range; possibly some cause for long-term concern due to declines or other factors.

Summary

Did you know?

Margaritifera means "pearl-bearer." The city of Pearl River, NY was probably named for pearls taken from this species in nearby Muddy Brook (Strayer and Jirka 1997).

State Ranking Justification

Most populations are scattered and contain very few individuals. At present there are healthy populations from the Salmon River near Plattsburg, the Grass River and its tributaries, and Fish Creek. The species is subject to a number of threats statewide and the healthy populations are restricted in range in the state.

Short-term Trends

There are larger populations in the Salmon River, Grass River and its tributaries, and Fish Creek documented since in the late 1990s. Additional rivers in central NY and Saratoga county have smaller populations (New York Natural Heritage Program 2019). Other undiscovered populations may occur throughout eastern New York in nutrient poor, softwater trout streams (Strayer and Jirka 1997).

Long-term Trends

A population in a tributary of the Hudson River in southern New York illustrates the general decline of this species. It had been known to occupy the Hackensack River basin in Rockland County since the mid 1800s and appeared to be thriving as recently as the 1950s. However by the early 1990s only 3 individuals were found and it was soon expected to become extirpated from this locale, probably as a result of the intense urbanization of the watershed (Strayer 1994; Strayer and Jirka 1997).

Conservation and Management

Threats

The single most important cause of the decline of freshwater mussels during the last century is the destruction of their habitat by siltation, dredging, channelization, impoundments, and pollution. A healthy fish assemblage is critical to viable mussel populations and dams have resulted in heavy losses of mussels, mainly due to elimination of host fish species. Erosion due to deforestation, poor agricultural practices, and the destruction of riparian zones causes an increase in siltation and shifting substrates that can smother mussels. Domestic sewage, acid mine runoff, heavy metals, pesticides, and effluents from paper mills, tanneries, chemical industries and steel mills have all been implicated in the destruction of native mussel fauna. Since the Eastern Pearlshell inhabits coldwater trout streams, eutrophication has been a significant cause of its decline worldwide. In particular, mortality of adults increased with higher concentrations of nitrates in the water and lowered survival and poor establishment of juveniles was related to the amount of phosphates and calcium (Bauer 1988).

Conservation Strategies and Management Practices

When feasible, the removal of impoundments in order to restore rivers to their natural flow would be beneficial since these structures negatively effect required fish host species as well as the mussels themselves. Since this species appears to be sensitive to eutrophication, actions which reduce run-off into high quality trout streams could be beneficial.

Research Needs

There is still much to learn about this species, especially determination of its distribution with respect to its Salmonid host fish species. Details about habitat requirements (current speed, water depth, substrate grain size, substrate stability, water temperature, and water quality factors) also need investigation. However, Strayer et al. (1994) found that the distribution of Unionoids was not related to these typical physical habitat qualities, but instead was related to long term stability of the substrate (i.e., flow refuges) and other large-scale habitat variables such as riparian zone vegetation (i.e., grassy vs. forested). Both large and small-scale forces promoting the patchy occurrence of Unionoid mussel beds is an active area of research (Strayer et al. 2004).

Habitat

Habitat

Generally this species lives buried in clean, mixed substrates in fast-flowing unpolluted trout streams and smaller rivers. Since Salmonids are the host species, it is confined to coldwater, nutrient-poor habitats, where it is often the only Unionoid species. Boulder-stabilized refugia containing enough sand for burrowing are ideal microhabitats for juveniles since they cannot tolerate silty conditions (Hastie et al. 2004).

Associated Ecological Communities

  • Confined river* (guide)
    The aquatic community of relatively large, fast flowing sections of streams with a moderate to gentle gradient. * probable association but not confirmed.

Associated Species

  • Eastern Elliptio (Elliptio complanata)

Range

New York State Distribution

New York forms the southwestern extent of this species' range. Within the state, its distribution is poorly known, but it seems rather widespread along the margins of the Adirondacks. At present, scattered populations are known from the Grass River and its tributaries, Fish Creek, the Boquet and Salmon Rivers south of Plattsburgh, a few rivers in central NY, the Upper Delaware River, and the Hackensack River (Strayer and Jirka 1997).

Global Distribution

The Eastern Pearlshell has a Holarctic distribution, occurring in northern Europe, eastern North America, and Eurasia. In North America it is distributed from Newfoundland and Labrador south to Pennsylvania. It is also known from Idaho and Wyoming. The Eastern Pearlshell is widespread in New England and the Canadian Maritime Provinces (Clarke 1981). Strayer (1987) hypothesized that the distribution of this species may be explained by its movement between drainages, and even continents, by anadromous ocean-going Salmonids, although it not known whether glochidia could survive such conditions.

Best Places to See

  • Salmon River

Identification Comments

General Description

The Eastern Pearlshell has a thick subelliptical, elongate shell which is arched and is up to 150 mm long. The beak sculpture is coarse and concentric. The periostracum is dark brown to black, without rays. The pseudocardinals are strong, but laterals nearly to entirely absent. The nacre is pearly white, sometimes with pink to purplish coloration (Strayer and Jirka 1997).

Identifying Characteristics

The Eastern Pearlshell is the only member of the family Margaritiferidae in the state, and its biology and distribution are unique among Unionoids in New York.

Characters Most Useful for Identification

The shell has a blackish, rayless periostracum and conspicuous pores on the shell interior (Strayer and Jirka 1997).

Best Life Stage for Proper Identification

Adult.

Behavior

Adults of this species are sessile, with only limited movement in the substrate. Passive downstream movement may occur when they are displaced from the substrate during floods. More major dispersal occurs while glochidia are encysted on their Salmonid hosts. Being ectothermic, mussels presumably have reduced activity levels during colder months of the year. The Eastern pearlshell is thought to be the longest-lived invertebrate animal; the maximum lifespan was observed to be 132 years and the mean age of sexual maturity is 20 years (Bauer 1992). This species has a very high fecundity (upward of 17 million glochidia produced annually) and the smallest glochidia (Bauer 1987).

Diet

Adult mussels are filter feeders. Algae, detritus, and bacteria are all important food sources. Mussels in turn are eaten by muskrats, raccoons, fish, and birds. Several different Salmonid fishes including Brook and Brown Trout serve as glochidial (larval) hosts (Strayer and Jirka 1997).

Best Time to See

Little is known about the activity periods of Unionoid mussels but they are presumed to be greatly reduced during cold times of the year. Freshwater mussels are most often easiest to locate during late summer when water levels are lowest.

  • Present
  • Reproducing

The time of year you would expect to find Eastern Pearlshell present and reproducing in New York.

Similar Species

  • Eastern Elliptio (Elliptio complanata)
    The shell of E. complanata is not arched, has a mostly brownish periostracum, with well developed lateral teeth and fine color rays.

Eastern Pearlshell Images

Taxonomy

Eastern Pearlshell
Margaritifera margaritifera (Linnaeus, 1758)

  • Kingdom Animalia
    • Phylum Mollusca (Mollusks)
      • Class Bivalvia (Bivalves)
        • Order Unionoida (Freshwater Mussels)
          • Family Margaritiferidae (Pearl Mussels)

Additional Resources

References

Bauer, G. 1987. Reproductive strategy of the freshwater pearl mussel Margaritifera margaritifera. Journal of Animal Ecology 56:691-704.

Bauer, G. 1988. Threats to the freshwater pearl mussel Margaritifera margaritifera. Biological Conservation 45:239-253.

Burch, J.B. 1975. Freshwater unionacean clams (mollusca: pelecypoda) of North America. Malcological Publications. Hamburg, Michigan. 204 pp.

Clarke, A.H. 1981a. The freshwater mollusks of Canada. National Museum of Natural Sciences, National Museums of Canada, D. W. Friesen and Sons, Ltd.: Ottawa, Canada. 446 pp.

Clarke, A.H. and C.O. Berg. 1959. The freshwater mussels of central New York. Cornell University Agricultural Experiment Station Memoir 367.

Hastie, L.C., P.J. Boon, and M.R. Young. 2000. Physical microhabitat requirements of freshwater pearl mussels, Margaritifera margaritifera. Hydrobiologie 429:59-71.

New York Natural Heritage Program. 2019. New York Natural Heritage Program Databases. Albany, NY.

Strayer, David L. 1987. Ecology and zoogeography of the freshwater mollusks of the Hudson River basin. Malacological Review 20:1-68.

Strayer, David L. 1994. Current status of unionacean clam populations in the Upper Passaic River basin, New York. Report to the New York Natural Heritage Program.

Strayer, David L. and K.J. Jirka. 1997. The Pearly Mussels (Bivalva: Unionoidea) of New York State. New York State Museum Memoir 26. The New York State Education Department.

Strayer, David L., D.C. Hunter, L.C. Smith, and C.K. Borg. 1994. Distribution, abundance, and roles of freshwater clams (Bivalva, Unionidae) in the freshwater tidal Hudson River. Freshwater Biology 31:239-248.

Strayer, David L., J.A. Dowling, W.R. Haag, T.L. King, J.B. Layzer, T.J. Newton and S.J. Nichols. 2004. Changing perspectives on Pearly Mussels, North America's most Imperiled Animals. BioScience 54:429-439.

Links

About This Guide

This guide was authored by: Jeffrey D. Corser

Information for this guide was last updated on: May 21, 2019

Please cite this page as:
New York Natural Heritage Program. 2019. Online Conservation Guide for Margaritifera margaritifera. Available from: https://guides.nynhp.org/eastern-pearlshell/. Accessed July 21, 2019.

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