Ensis

A Vulnerable genera from the “Molluscs” group, mostly found in Gravelly Sand

Gravelly Sand

Vulnerable

Molluscs

Genera Characteristics Recorded Traits Possible Values
Size in cm
  • 11-20 cm
  • <1 cm
  • 1-10 cm
  • 11-20 cm
  • >20 cm
Genera Characteristics Recorded Traits Possible Values
Motility (Adult)
  • Short Range Mobility
  • Adult
  • Short Range Mobility
  • Sedentary

“Short Range Mobility”

Motility (Larval)
  • Long Term Planktonic
  • Long Term Planktonic
  • Short Term Planktonic
  • Brooded or Laid Eggs

“Long Term Planktonic”

Lifespan
  • >10 years
  • >10 years
  • 3-10 years
  • 1-2 years
  • <1 year
Maturity
  • 1-2 years
  • >4 years
  • 3-4 years
  • 1-2 years
  • <1 year
Fecundity
  • 100 - 1000 (Estimated)
  • 1000 - 10000 (Estimated)
  • 1 - 10
  • 10 - 100
  • 100 - 1000
  • 1000 - 10000
  • 10000 - 1 million
  • > 1 million

estimated

estimated

Image: Ensis © MES

Vulnerability

Ensis is a genus of bivalve belonging to the Family Pharidae (Razor shells) & lives by filtering plankton from the overlying water column. The adult shell size is 11-20cm & the bivalve burrows to a considerable depth in sand & shell gravel. It has a restricted mobility but is able to re-burrow following disturbance. It occurs in relatively high densities in shallow waters extending into the intertidal zone, but has also been recorded as isolated specimens down to depths of 60m. This shellfish is vulnerable to disturbance by dredging, but is probably able to migrate vertically through sediments mobilised by the dredging process.

 

Recoverability

Ensis is a long-lived genus with a life-span of up to 10-20yrs. The age at maturity is 1 year and breeding takes place between February & April. The eggs are approximately 70mm in diameter & are fertilised externally after which the 0.25mm planktotrophic larvae spend up to 30 days in the water column. There is little information on fecundity & larval dispersal potential but in Chile Ensis is known to produce 14-19 million eggs in a lifetime so fecundity may be high. Based on the relatively long time before adult razor shells breed, their slow growth rate & long life-span, Ensis has a low potential for recovery.

 

References

  • Biology

    • Armonies & Reise, 1999
    • Fish & Fish, 1996
    • Hayward & Ryland, 1990
    • Hayward et al., 1996
    • Henderson & Richardson, 1994
    • Robinson & Richardson, 1998
  • Taxonomy

    • Fish & Fish, 1996
    • Hayward et al., 1996
    • Howlett, 1990
    • JNCC, 1999
  • Distribution

    • Armonies & Reise, 1999
    • Fish & Fish, 1996
    • Hayward & Ryland, 1990
    • Hayward et al., 1996
    • Henderson & Richardson, 1994
    • Holme, 1954
  • Reproduction

    • Armonies & Reise, 1999
    • Avellanal et al., 2002
    • Fahy & Gaffney, 2001
    • Fish & Fish, 1996
    • Gaspar & Monteiro, 1998
    • Hayward et al., 1996
    • Henderson & Richardson, 1994
    • Newell & Newell, 1977
    • Palmer, 2004