Ensis ensis

Researched ByJacqueline HillData Supplied ByMarLIN
Refereed byThis information is not refereed.
Taxonomy
Scientific nameEnsis ensisCommon nameA razor shell
MCS CodeW1999Recent Synonyms
PhylumMolluscaSubphylum
SuperclassClassPelecypoda
SubclassOrderVeneroida
SuborderFamilyPharidae
GenusEnsisSpeciesensis
Subspecies  
Additional Information
Taxonomy References
General Biology
Growth formBivalvedFeeding methodActive suspension feeder
Mobility/MovementBurrowerEnvironmental positionInfaunal
Typical food typesSuspended organic detritusHabitBurrow dwelling
BioturbatorFlexibilityNone (< 10 degrees)
FragilityFragileSizeMedium(11-20 cm)
HeightInsufficient informationGrowth Rate2-4 cm/year
Adult dispersal potential10-100mDependencyIndependent
SociabilityGregarious
Toxic/Poisonous?No
Additional InformationTypical abundance
Abundance of Ensis sp. varies from high to low density. In favourable conditions - such as the lee of rocks, rocks and islands for Ensis arcuatus on the western coast, individuals are found in high densities in 'beds' which interchange individuals with the surrounding areas where they occur in a more dispersed pattern (Fahy et al. in press).

Size ranges
Size range given for Ensis ensis. Ensis siliqua males and females up to 20 cm and Ensis arcuatus males and females up to 15 cm.

Growth rates
Growth in the first winter is 2-4 cm. The three species have similar growth patterns but with different asymptotic lengths. In Ensis siliqua males grow faster than females. Growth rates are higher in the summer, when the food supply is abundant, than in the winter when the temperature and food supply are both reduced. Ensis ensis also show a neap-spring lunar growth pattern with smaller growth bands during spring tides when animals are emersed for longer (Henderson & Richardson, 1994). The growth rate given is the maximum rate in the first year or two of life. Thereafter growth falls to 2-3 cm/year (Robinson & Richardson, 1998).

Biology References
Distribution and Habitat
Distribution in Britain & IrelandCommon on all British coasts.
Global distributionFrom Norway to the Atlantic coast of Spain. Ensis ensis and Ensis siliqua found in some parts of the Mediterranean.
Biogeographic rangeNot researchedDepth rangeto a depth of 60m
MigratorySee additional information
Distribution Additional Information
  • Habitat
    Ensis spp. Occur virtually everywhere inshore but favourable conditions, such as the lee of reefs, rocks and islands make for high densities known as 'beds' which interchange individuals with the surrounding areas where they occur in a more dispersed pattern. Ensis ensis beds do occur at extreme low water of spring tides but the species is much more common in depths of about 10m (Holme, 1954). Single specimens have been collected from depths of 60m in the Plymouth area. Ensis arcuatus lives in coarser sediment than either Ensis ensis or Ensis siliqua.
  • Migration
    Henderson & Richardson (1994) observed a distribution of razor clam size classes on a shore in north Wales which may indicate that there is a gradual down-shore migration of juveniles into the adult population. They suggest that juveniles become established further up the shore because the low water mark is exposed to the strongest tidal currents.
  • Wave exposure
    In moderate wave exposure Ensis ensis may be replaced by the larger Ensis siliqua (Holme, 1954).
Substratum preferencesFine clean sand, Coarse clean sandPhysiographic preferencesOpen coast, Offshore seabed, Strait / sound, Enclosed coast / Embayment
Biological zoneLower Eulittoral, Sublittoral Fringe, Upper Infralittoral, Lower Infralittoral, Upper Circalittoral, Lower CircalittoralWave exposureSheltered, Very Sheltered, Extremely Sheltered, Ultra Sheltered
Tidal stream strength/Water flowModerately Strong (1-3 kn), Weak (<1 kn)SalinityFull (30-40 psu)
Habitat Additional InformationHabitat
Ensis spp. occur virtually everywhere inshore but favourable conditions, such as the lee of reefs, rocks and islands make for high densities known as 'beds' which interchange individuals with the surrounding areas where they occur in a more dispersed pattern. Ensis ensis beds do occur at extreme low water of spring tides but the species is much more common in depths of about 10 m (Holme, 1954). Single specimens have been collected from depths of 60 m in the Plymouth area. Ensis arcuatus lives in coarser sediment than either Ensis ensis or Ensis siliqua.

Migration
Henderson & Richardson (1994) observed a distribution of razor clam size classes on a shore in north Wales which may indicate that there is a gradual down-shore migration of juveniles into the adult population. They suggest that juveniles become established further up the shore because the low water mark is exposed to the strongest tidal currents.

Wave exposure
In moderate wave exposure Ensis ensis may be replaced by the larger Ensis siliqua (Holme, 1954).
AMBI Group (Borja et al., 2000)I 
Distribution References
Reproduction/Life History
Reproductive typeGonochoristic Developmental mechanismPlanktotrophic
Reproductive SeasonSummerReproductive LocationInsufficient information
Reproductive frequencyAnnual episodic Regeneration potentialNo
Life span11-20 yearsAge at reproductive maturity3-5 years
Generation timeInsufficient informationFecundityInsufficient information
Egg/propagule sizeInsufficient informationFertilization typeInsufficient information
Larvae/Juveniles
Larval/Juvenile dispersal potentialInsufficient informationLarval settlement periodInsufficient information
Duration of larval stage1-2 months  
Additional InformationLife span
The life span of Ensis ensis is likely to be in excess of 10 years. The other two British species Ensis siliqua and Ensis arcuatus are also very long-lived, with a life-span up to 18 years (E. Fahy pers. comm.).

Reproduction
Razor shells in Britain do not appear to breed before they are three years old (Henderson & Richardson, 1994). Breeding occurs during the summer but larval settlement is not successful every year, and recruitment of juveniles is irregular (Hayward et al., 1996). Breeding probably occurs during spring and the veliger larvae has a pelagic life of about a month (Fish & Fish, 1996). Studies on razor shells from North Wales showed that individuals of Ensis ensis were mature in July but were spent in August, indicating that spawning had occurred by the middle of the summer (Henderson & Richardson, 1994).
Reproduction References