Mya arenaria

Researched ByLizzie TylerData Supplied ByUniversity of Sheffield
Refereed byThis information is not refereed.
Taxonomy
Scientific nameMya arenariaCommon nameSand gaper
MCS CodeW2149Recent SynonymsNone
PhylumMolluscaSubphylum
SuperclassClassPelecypoda
SubclassOrderMyoida
SuborderMyinaFamilyMyidae
GenusMyaSpeciesarenaria
Subspecies  
Additional InformationCommon names include, the 'sand gaper', 'soft clam', 'soft-shelled clam', 'steamer clam' and the 'nannynose'. The literature on Mya arenaria is extensive and this Key Information review is based upon more detailed reviews by Clay (1966), Newell & Hidu (1986) and Strasser (1999).
Taxonomy References Fish & Fish, 1996, Howson & Picton, 1997, Campbell, 1994, Hayward et al., 1996, Tebble, 1976, Foster-Smith, 2000, Turk & Seaward, 1997, Allen, 1962, Bruce et al., 1963, Newell & Hidu, 1986, Strasser, 1999, Clay, 1966, Anonymous, 1996, Hawkins, 1994
General Biology
Growth formBivalvedFeeding methodPassive suspension feeder, Active suspension feeder
Mobility/MovementBurrowerEnvironmental positionInfaunal
Typical food typesPhytoplankton, small zooplankton, benthic diatoms, suspended particulates and dissolved organic matter.HabitBurrow dwelling
BioturbatorFlexibilityNone (< 10 degrees)
FragilityIntermediateSizeMedium(11-20 cm)
HeightInsufficient informationGrowth RateSee additional information
Adult dispersal potential100-1000mDependencyIndependent
SociabilitySolitary
Toxic/Poisonous?No
Additional InformationMya arenaria populations demonstrate pronounced patchiness, e.g. in the Dutch Wadden Sea its abundance varies from high to low. Patchiness seems to be typical in Mya arenaria and has been reported from Sweden and North America (Strasser et al.,1999; Strasser pers. comm.).

Growth rates: Mya arenaria generally grows fastest in its first years with growth rate decreasing with age, although linear rates of growth have also been reported (Strasser, 1999). Growth is rapid in favourable conditions but rates vary with location, e.g. Mya sp. grew to 51 mm in 6-7 years in Alaska, but this size was attained in 1.5 years in Connecticut (Brousseau & Baglivo, 1987). Similarly, marketable size ( 4-5 cm long) was reached within 1.5 years in Chesapeake Bay, but took 5 years in New Brunswick, Canada. Growth rates are affected by population density, sediment type, salinity, emergence time, water flow rates, disturbance, latitude and pollution (Newell & Hidu, 1986; Strasser, 1999).

Seasonal growth rates: growth is generally greatest in late spring and early summer and slowest in cold winters e.g. in New England (Newell & Hidu, 1986). Rapid growth is correlated with the phytoplankton bloom and therefore food availability but may also be affected by temperature and spawning (Stickney, 1964; Brousseau, 1979; Newell & Hidu, 1986).
Biology References Fish & Fish, 1996, Campbell, 1994, Hayward et al., 1996, Tebble, 1976, Newell & Hidu, 1986, Strasser, 1999, Brousseau & Baglivo, 1987, Brousseau, 1979, Stickney, 1964, Clay, 1966, Brousseau, 1987, Newell, 1982, Armonies, 1994, Brousseau, 1978(b), Kühl, 1981, Gibbons & Blogoslawski, 1989, Anonymous, 1996, Hawkins, 1994, Kammermans, 1994, Dow & Wallace, 1961, Beukema, 1995, McLaughlin & Faisal, 2000, Hayward & Ryland, 1990
Distribution and Habitat
Distribution in Britain & IrelandFound on all British coasts but is not recorded from the Isles of Scilly.
Global distributionFound on the European coast from the White Sea to northern Norway, in the Baltic Sea and Wadden Sea to Portugal as well as the Black Sea. Reported from Labrador to Georgia in the W. Atlantic and from North Sound, Alaska to California in the E. Pacific.
Biogeographic rangeNot researchedDepth range0 - 20 m
MigratoryNon-migratory / Resident
Distribution Additional InformationThe southern distribution of Mya arenaria may be restricted by a limit of 28 °C for both adults and larvae (Newell & Hidu, 1986; Strasser, 1999). Various authors suggested that the northern distribution was limited by critical spawning temperature of 10-12 °C and 12-15 °C required for larval development, however, Strasser (1999) noted some exceptions and concluded that this hypothesis needed further examination.

Distribution: Mya arenaria is found most abundantly in intertidal and shallow subtidal areas but can reach 192 m depth in the subtidal (Strasser, 1999). The majority of clams >50 mm are found in sediment between 15 - 20 cm deep in the Wadden Sea, but may burrow up to 40 cm deep. As they grow adults live deeper in the sediment, their siphons growing accordingly and large clams establish a permanent burrow. Young clams (up to 50 mm) can burrow again if disturbed. However the foot becomes much reduced and shorter in larger specimens. With increasing size it becomes more difficult for exposed specimens to raise the shell into position and therefore. if disturbed, fewer large than small individuals manage to reburrow. For example, 62% of small clams (35-50mm), 39% of medium sized (51-65 mm) and only 21% of large clams (66-75 mm) had reburrowed within 48 hours (Pfitzenmeyer & Drobeck, 1967).

Mya arenaria grows faster in fine rather than coarse sediments and fastest in sand or sandy mud. The clam has difficulty burrowing in sediments larger than 0.5 mm (coarse sand). Areas with fast currents support highest densities and growth rates whereas excessive silt reduces growth rates (Newell & Hidu, 1986). Densities of adults vary between years and location, e.g. Clay (1966) reported adult densities between ca 5 /m² to 300 /m² in the UK and Strasser et al. (1999) reported abundances between 0-243 individuals /m² (with a mean of 11.8 individuals /m²) in the Wadden Sea. Strasser et al. (1999) concluded that the Wadden Sea population is greatest at the mid to low tidal level and resulted from larval settlement. Its patchy distribution and dominance of single year classes being due to wind direction during peaks of larval settlement, and when juvenile predation is low. Clams that survive the first year may reach several years of age but mass mortalities may occur at any time, due to indeterminate causes (Strasser et al, 1999).

Global distribution: Mya arenaria became extinct on the east coasts of the Pacific and Atlantic during the glaciations of the Pleistocene. It subsequently colonized the European coast between the 13 th and 17 th centuries, possibly introduced by the Vikings (as food or bait) (Eno et al., 1997; Eno et al., 2000; Strasser, 1999). Mya arenaria has been reported from Kamchatka to southern Japan and China, however these records may have been confused with Mya japonica (Strasser, 1999). Strasser (1999) also regarded additional records from Iceland, the Mediterranean and Florida as dubious. Mya arenaria probably invaded the Pacific east coast as a by-product of oyster transplants but was later intentionally introduced as a commercial fishery. It was probably introduced into the Black Sea around 1960 as larvae in the ballast waters of Baltic Sea tankers (Strasser, 1999) . Strasser (1999) notes that although introduction may have been effected by man its present distribution is also the result of significant natural expansion.

Substratum preferencesMuddy gravel, Coarse clean sand, Fine clean sand, Muddy sand, Mud, Mixed, Sandy mudPhysiographic preferencesStrait / sound, Sealoch, Ria / Voe, Estuary, Enclosed coast / Embayment
Biological zoneMid Eulittoral, Lower Eulittoral, Sublittoral Fringe, Upper Infralittoral, Lower Infralittoral, Upper Circalittoral, Lower CircalittoralWave exposureExposed, Moderately Exposed, Sheltered, Very Sheltered
Tidal stream strength/Water flowModerately Strong (1-3 kn), Weak (<1 kn)SalinityFull (30-40 psu), Low (<18 psu), Reduced (18-30 psu), Variable (18-40 psu)
Habitat Additional Information
AMBI Group (Borja et al., 2000)II 
Distribution References Fish & Fish, 1996, Campbell, 1994, Hayward et al., 1996, Tebble, 1976, Foster-Smith, 2000, Turk & Seaward, 1997, Crothers, 1966, Allen, 1962, Seaward, 1982, Seaward, 1990, Bruce et al., 1963, Newell & Hidu, 1986, Strasser, 1999, Eno et al., 1997, Clay, 1966, Newell, 1982, Armonies, 1994, Kühl, 1981, Anonymous, 1996, Strasser et al., 1999, Hawkins, 1994, Dow & Wallace, 1961, Pfitzenmeyer & Drobeck, 1967, Hayward & Ryland, 1990
Reproduction/Life History
Reproductive typeGonochoristic Developmental mechanismPlanktotrophic
Reproductive SeasonSee additional informationReproductive LocationWater column
Reproductive frequencyAnnual protracted Regeneration potentialNo
Life span11-20 yearsAge at reproductive maturity3-5 years
Generation time3-5 yearsFecundity100000- 5000000
Egg/propagule size66 µm diameterFertilization typeExternal
Larvae/Juveniles
Larval/Juvenile dispersal potential>10kmLarval settlement periodInsufficient information
Duration of larval stage11-30 days  
Additional InformationA life span of 10-12 years was considered normal, although a maximum of 28 years was recorded in the Bay of Fundy (Strasser, 1999). Commito (1982) suggested that Mya sp. delayed reproduction until its fourth year, preferring rapid growth to reach a depth refuge. Strasser (1999) reported that first reproduction usually occurred at a size of about 20 -50 mm, which corresponds to an age of about 1-4 years depending on growth conditions.
Spawning: Spawning occurs once or twice annually, usually starting in spring and can occur between March and November depending on locality. In European waters larvae are usually found in May and June but sometimes as late as October. Annual spawning was reported in the Wadden Sea, on the west coast of Sweden, the east coast of Denmark and the Black Sea whereas biannual spawning was reported in Oslofjord and the south coast of England (Warwick & Price, 1976; Strasser, 1999; and see Brousseau,1987 and Clay, 1966 for reviews).
Both temperature and food availability affect gametogenesis and spawning. Critical spawning temperatures of 10-12 °C were suggested by Nelson (1928) however, peak spawning occurs in Massachusetts at 4-6 °C (Brousseau, 1978a). Peaks of larvae have been observed at 20°C and second spawnings once temperature had dropped below 25 °C (Newell & Hidu, 1986). Optimum larval growth has been reported between 17 -23 °C in the laboratory (Stickney, 1964) and slow growth between 12-15 °C (Loonsanoff & Davis, 1963). Strasser (1999) suggested that further study was required.
Fecundity: Males usually spawn first, releasing a pheromone which stimulates females to spawn (Newell & Hidu, 1986). Fecundity varies with location and size e.g. 120,000 eggs from a 60 mm clam, 3 million from a 63 mm clam and 1-5 million eggs in an individual have been reported (Strasser, 1999).
Fertilization: fertilization is external. Eggs are 66µm in diameter and can be carried many miles by the current (Newell & Hidu, 1986).
Larval stages: larval life lasts about 2-3 weeks, but can be extended, in the laboratory to up to 35 days in unfavourable conditions, most not metamorphosing until 200µm in length (Loosanoff & Davis, 1963; Strasser, 1999).
Recruitment: recruitment in bivalve molluscs is influenced by larval and post-settlement mortality. Mya arenaria demonstrates high fecundity, increasing with female size, with long life and hence high reproductive potential. The high potential population increase is offset by high larval and juvenile mortality. Juvenile mortality reduces rapidly with age (Brousseau, 1978b; Strasser, 1999). Larval mortality results from predation during its pelagic stages, predation from suspension feeding macrofauna (including conspecific adults) during settlement and deposition in unsuitable habitats. Mortality of the juveniles of marine benthic invertebrates can exceed 30% in the first day, and several studies report 90% mortality (Gosselin & Qian, 1997). Larval supply and settlement is often dependant on currents and timing of the phytoplankton bloom and may be sporadic in bivalves (see Cerastoderma edule reproduction) and differs consistently between sites. Recruitment is affected by adult population density, settlement intensity (in some but not all cases), post-settlement and juvenile predation, active and passive transport, and bedload transport or sediment erosion (Olafsson et al., 1994). For example:
  • in New Hampshire densities of spat ranged from 21 -8,200 /m² from 1975-1980 depending on the year (Newel & Hidu, 1986);
  • adults (up to 25 mm and occasionally 40 mm) and large numbers of juveniles were subject to bedload sediment transport (up to 790 individuals /m /day in sheltered sites and 2,600 individuals /m /day in exposed) in Nova Scotia;
  • in the above population bedload transport in exposed conditions accounted for 10 fold increase in clam density in September followed by a significant decrease by November and complete removal of newly settled spat (Emerson & Grant, 1991);
  • Brousseau (1978b) estimated that 0.1% of egg production survived to successful settlement;
  • Newell & Hidu (1986) suggested that <1% of settled spat must mature and reproduce in order to sustain the population;
  • high larval and juvenile mortality decreases with age and size levelling off towards age of first reproduction, with estimates of 88% mortality at 2-4.9 mm falling to <10% at >30 mm, and is highest in summer when predators are most abundant (Brousseau, 1978b; Strasser, 1999);
  • high densities of settling spat on a shallow exposed shore in southern Sweden in summer were swept away by storms in autumn and early winter (Olafsson et al.,1994);
  • predation was blamed for a reduction in newly settled spat from 6000/m² to zero in the subtidal in Virginia (Lucy, 1976 cited by Newell & Hidu, 1986);
  • Strasser et al., (1999) noted that sites of high adult densities do not deter settling spat or prevent successful recruitment, but the presence of Arenicola marina may prevent development to adulthood due to bioturbation.
Reproduction References Newell & Hidu, 1986, Strasser, 1999, Brousseau & Baglivo, 1987, Brousseau, 1979, Stickney, 1964, Clay, 1966, Brousseau, 1987, Warwick & Price, 1975, Brousseau, 1978(a), Loosanoff et al., 1966, Loosanoff & Davis, 1963, Lutz et al., 1982, Emerson & Grant, 1991, Gosselin & Qian, 1997, Brousseau, 1978(b), Kühl, 1981, Anonymous, 1996, Strasser et al., 1999, Hawkins, 1994, Dow & Wallace, 1961, Nelson, 1928, Olafsson et al., 1994., Commito, 1982, Eckert, 2003, Brousseau, 1978(b), Strasser, 1999