Ascidia

A Intermediate genera from the “Other: Chordata” group, mostly found in Cobbles

Cobbles

Intermediate

Other: Chordata

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

“Sedentary”

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

“Short Term Planktonic”

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

Image: Ascidia © John Ryland

Vulnerability

Ascidia is a genus of solitary sessile sea squirts (Ascidiacea) of about 3-15cm height. In common with other ascidians, the genus feeds by filtering fine particulate material from the water column through a complex gill filtration system. This is vulnerable to clogging by excessive quantities of suspended material & the organism is also unable to reattach itself if the substrate is disturbed. It is likely to be vulnerable to disturbance by dredging & to deposition of sediment mobilised during the dredging process.
 

Recoverability

Ascidia has a life-span of 1-2yrs & produces relatively few yolk-filled eggs (typically 6-8 per adult) at annual breeding times that reach peaks in mid-summer. Fertilisation is external & after a short phase of 2-10 days in the plankton, the tadpole larvae select a suitable substratum for settlement & metamorphosis. Metamorphosis can be delayed during this site-selection phase until a suitable substratum is located, but rarely exceeds 10 days during which time the larvae can be dispersed by seabed currents for up to 10km. The relatively long life-span of 1-2yrs & the small number of larvae produced by this genus suggest that its recoverability is low, although the relatively widespread dispersion allows colonisation from outside the area of disturbance. This genus should probably be regarded as of intermediate recoverability.
 

References

  • Biology

    • Havenhand & Svane, 1989
    • Millar, 1970
  • Distribution

    • Havenhand & Svane, 1989
    • Havenhand, 1991
  • Reproduction

    • Havenhand & Svane, 1989
    • Havenhand, 1991
    • Millar, 1970
    • Svane & Lundalv, 1981
    • Svane & Young, 1989
    • Tarjuelo & Turon, 2004