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   Mya arenaria (mollusc)
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    Taxonomic name: Mya arenaria Linnaeus, 1758
    Synonyms: Mya hemphillii
    Common names: almindelig sandmusling (Denmark), eastern soft-shell clam (USA), hietasimpukka (Finland), liela smilšgliemene (Latvia), liiva-uurikkarp (Estonia), long-necked clam (USA), nannynose, sand gaper (USA), Sandklaffmuschel (Germany), sandmusslan (Sweden), sandskel (Iceland), smelinuke (Lithuania), soft-shell clam (USA), steamer clam (USA), vanlig sandskjell (Norway, Svalbard & Jan Mayan)
    Organism type: mollusc
    Mya arenaria (soft shell clam) has a large global distribution, largely due to its adaptability to varying environments. Impacts of Mya arenaria range from habitat alteration to massive bioaccumulation.
    Mya arenaria can grow to be 10-15cm long and 8-19cm wide with a white to pale grey shell which can be variable in colour depending on the sediment stratum it burrows into. The shell is thin and fragile, rounded in the front and forms a point at the rear hinge. The exterior of the shell is rough and has uneven concentric rings. The interior right valve has a deep pit, while the interior left valve has a "shelf-like projection" (chondrophore) which is used to distinguish it from many native Pacific bivalves. Two fused brown siphons that filter water are located at the posterior end of M. arenaria (Cohen, A. N., 2005).
    Similar Species
    Cryptomya californica, Mya truncata, Platyodon cancellatus, Schizothaerus nuttalli

    Occurs in:
    coastland, estuarine habitats, marine habitats
    Habitat description
    NOBANIS (undated) states that Mya arenaria is found in brackish waters, estuaries, and marine habitats. M. arenaria burrows into the sediment and can be found 20-30cm below the surface of the soil. It prefers sandy soils with a preference for a sandy-mud mixture with some gravel. If the substrate is too coarse then it cannot adequately burrow and may damage its thin shell (Cohen, 2005). Locations with clean, fast-flowing water sustain the highest populations of M. arenaria (Tyler-Walters, 2003). It is typically found in the upper intertidal zone to the lower intertidal zone, subtidal zone, and even in deep waters, up to 190m beneath the surface of the ocean (Tyler-Walters, 2003). It can survive between -2 and 28 ° Celsius, with optimal temperatures between 6-14 ° Celsius. Optimal salinity concentrations are between 25-35 parts per thousand with a tolerance as low as 5 parts per thousand. The soft-shell clam is also very tolerant of anaerobic environments and can survive in an oxygen depleted environment for up to 8 days (Cohen, 2005).
    General impacts
    NOBANIS (undated) reports that Mya arenaria competes with other species, causes abiotic changes, and uses resources. Other ecological impacts of M. arenaria include benthic-pelagic interaction, bioaccumulation, community dominance, and habitat change. (Baltic Sea Alien Species Database, 2007).
    The soft-shell clam Mya arenaria is harvested by humans for culinary purposes, like "clam bakes" which are common in areas in New England and Canada. It is not commonly eaten in Europe or the UK (JNCC, undated) or on US west coast (Dr. James (Jeb) Byers., pers.comm., May 2008). Byers (2005) hypothesized that this was one of the reasons M. arenaria was so much bigger in Washington state than anywhere on US east coast where clam is native (with less human harvest pressure the clam got bigger).

    M. arenaria is a valuable food source for migrating shorebirds along the Pacific coast of the United States (Carlton, 1977). Fish, sandworms, crabs, rays, sharks, flounder, gulls, sea otters, raccoons, and wading birds, (Tyler-Walters, 2003). Staghorn sculpin (Leptocottus armatus) also prey upon M. arenaria. M. arenaria is important to U.S. fishery (on the US east coast), and is also an important research species (Tyler-Walters, 2003). As a suspension feeder, it plays a crucial role in filtering and cleaning water sources, and can be used as a tool in regulating and enforcing pollution standards in water quality control (UK Biodiveristy Group, 1999).

    Geographical range
    Native range: Mya arenaria is native to the North American east coast from Labrador, Canada to Cape Hatteras, NC (Dr. James (Jeb) Byers., pers.comm., May 2008).
    Known introduced range: M. arenaria is reported in many parts of Europe: Baltic Sea (Baltic Sea Alien Species Database, 2007); Denmark, Estonia, Finland, Germany, Iceland, Latvia, Lithuania, Norway, Poland Svalbard and Jan Mayen and Sweden (NOBANIS, undated); UK, Spain (Cohen 2005). M. arenaria is introduced to many places along the Pacific coast of North America from Alaska on down to California (Dr. James (Jeb) Byers., pers.comm., May 2008).
    Introduction pathways to new locations
    Ship ballast water: The eggs and larval stages can be transported in the ballasts of ships. Mya arenaria was introduced to the west coast of U.S. via ship ballast water (Carlton, 1977).
    Ship/boat hull fouling: NOBANIS (undated) states that Mya arenaria was introduced to Estonia by hull fouling considered a primary vector for transporting species.
    Stocking: It is widely believed that some stock of Mya arenaria was unintentionally introduced when transporting stock of American oyster (Crassostrea virginica) to the West coast of the United States . (Stearns, 1881).

    Local dispersal methods
    Natural dispersal (local): In Britain, Mya arenaria spread by the natural dispersal of larvae (JNCC, undated).
    Management information
    Preventative measures: A two year study undertaken for the Department of Environment and Heritage, Australia by CSIRO (Commonwealth Scientific and Industrial Research Organisation) Marine Research, was designed to identify and rank introduced marine species found within Australian waters (potential domestic target species) and those that are not found within Australian waters (potential international target species). Potential domestic target species, in this context are defined as ship-vectored, established, non-native (or cryptogenic) species that have demonstrated significant impact on human health, economic interests or environmental values in the Australian marine environment. Potential international target species are similarly defined as ship vectored, non-native (or cryptogenic) species that have demonstrated significant impacts outside of Australia. All of the non-native potential target species identified in the independent report published are ranked as high, medium and low priority, based on their invasion potential and impact potential.
    The potential international target species are prioritised by their location in the invasion potential/impact potential space. Mya arenaria has been categorised as 'Low priority'. (Hayes et al. 2005).

    Human use in fisheries for harvest as a food source has made this species well established in its non-native range, making eradication infeasible (Hoagland & Jin, 2006).

    Physical: Management reccomendations include remediation of over-harvested and polluted sites to reestablish an increase in species biodiversity, thereby maintaining predation interaction (UK Biodiveristy Group, 1999).

    The soft-shell clam is an active suspension feeder, filtering organic particles and microinvertabrates, like plankton, filamentous algae, diatoms, jellyfish and fish larvae, and flagellates. It feeds using two fused siphon tubes that draw in water to be strained with micro-cilia. The water is then forced back out through the siphon. An adult soft-shell clam can filer up to 50 liters of water per day (Tyler-Walters, H., 2003). Excessive siltation reduces feeding efficiency by clogging the gills of M. arenaria (Palacioset al, 2000).
    Separate male and female sexes occur in the species, with fertilization occurring externally in the environment. Female soft shell clams can release from 1-5 million eggs in its lifetime and typically one to two spawnings happen a year, one in early spring and the other in late summer, depending on locality and monthly tidal cycles (Abraham & Dillon, 1986). Temperature is the crucial factor in reproduction with optimal temperatures between 10-15° Celsius (Cohen, 2005). Fecundity also increases with size and age, particularly with females (Tyler-Walters, 2003).
    Lifecycle stages
    Approximately 12 hours after fertilization, the larval forms of Mya arenaria hatch from the eggs (Cohen, 2005). High juvenile and larval mortality are common due to high egg production (Tyler-Walters, 2003). The larvae spend 2-5 weeks free-floating with plankton and other organic particles before metamorphosizing and settling to the bottom of the sea floor. The clams then spend another 2-5 weeks moving along the sea floor or temporarily attaching itself to the surface of objects. M. arenaria then begins to burrow into the sediment and stays burrowed for the rest of its life (Cohen, 2005). Young soft-shell clams can reborrow if disturbed, but aduls cannot because of their large shell size (Tyler-Walters, 2003). M. arenaria reaches maturity in 1-4 years, depending on the length of each growing season. The typical lifespan is between 10-12 years, but cases have been recorded of some soft-shell clams reaching 28 years of age (Cohen, 2005).
    Reviewed by: Dr. James (Jeb) Byers, Assistant Professor, Dept. of Zoology, Department of Zoology University of New Hampshire. USA
    Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Tuesday, 31 July 2007

ISSG Landcare Research NBII IUCN University of Auckland