BIOTIC Species Information for Idotea pelagica
Researched byAndrew Hosie Data supplied byMarLIN
Refereed byThis information is not refereed.
Scientific nameIdotea pelagica Common nameAn isopod
MCS CodeS942 Recent Synonyms

PhylumArthropoda SubphylumCrustacea
Superclass ClassMalacostraca
SubclassEumalacostraca OrderIsopoda
Suborder FamilyIdoteidae
GenusIdotea Speciespelagica

Additional Information
Taxonomy References Naylor, 1972, Hayward & Ryland, 1995b, Picton & Howson, 1997,
General Biology
Growth form Feeding methodOmnivore
Environmental positionEpifaunal
Typical food typesOmnivorous; fucoid algae, associated epiphytes, barnacle cirri. HabitFree living
BioturbatorNot relevant FlexibilityLow (10-45 degrees)
FragilityIntermediate SizeSmall(1-2cm)
HeightNot researched Growth RateNot researched
Adult dispersal potentialInsufficient information DependencyIndependent
SociabilitySolitary Host forParasitised by Clypeoniscus hanseni (Isopoda, Cryptoniscoidea).
General Biology Additional Information
Biology References Naylor, 1972, Naylor, 1955, Leifsson, 1999, Kroer, 1986, Healy & O'Neill, 1984, Sheader, 1977,
Distribution and Habitat
Distribution in Britain & IrelandFound on all British and Irish coasts.
Global distributionFound from Iceland, Norway south to Spanish coast of the Bay of Biscay, not found in the Baltic.
Biogeographic rangeArctic-boreal to temperate. Depth range0-10 m
MigratoryNon-migratory / Resident   
Distribution Additional Information

Substratum preferencesAlgae
Physiographic preferencesOpen coast
Biological zoneUpper Eulittoral
Mid Eulittoral
Lower Eulittoral
Sublittoral Fringe
Upper Infralittoral
Lower Infralittoral
Upper Circalittoral
Wave exposureVery Exposed
Tidal stream strength/Water flowInsufficient information
SalinityFull (30-40 psu)
Habitat Preferences Additional InformationThere are a total of 8 members of Idotea in British waters which can be distinguished using the keys provided in Naylor (1972) and Hayward & Ryland (1995b). The various species are not typically sympatric, but are ecologically segregated. For example, Idotea pelagica is found in the lower intertidal and shallow subtidal on exposed rocky reefs and is replaced in less exposed areas by I. granulosa which in turn is replaced by I. chelipes on sheltered, estuarine shores (Naylor, 1955).
Distribution References Naylor, 1972, Hayward & Ryland, 1995b, Bruce et al., 1963, MBA, 1957, Picton & Howson, 1997, NBN, 2002, Naylor, 1955, Leifsson, 1999, Kroer, 1986, Healy & O'Neill, 1984, Sheader, 1977,
Reproduction/Life History
Reproductive typeGonochoristic
Developmental mechanismDirect Development
Reproductive SeasonSee additional information Reproductive LocationSediment surface
Reproductive frequencyAnnual protracted Regeneration potential Yes
Life span1-2 years Age at reproductive maturity<1 year
Generation time<1 year Fecundity10-100
Egg/propagule sizeInsufficient information Fertilization typeInternal
Larval/Juvenile dispersal potentialInsufficient information Larval settlement periodSee additional information
Duration of larval stageSee additional information   
Reproduction Preferences Additional Information
  • Reproductive season
  • The reproductive season of Idotea pelagica is closely linked to temperature (Leifsson, 1999). Reproductive effort is at its greatest during periods when the sea water temperature is between 5 and 12 °C (Sheader, 1977; Healy & O’Neill, 1984; Leifsson, 1999). While ovigerous females are found all year round in southern Irish coasts, the highest proportion of ovigerous females are found between December and August (Healy & O’Neill, 1984), while on the Northeast coast of England ovigerous females were found only between April and August (Sheader, 1977). Icelandic populations have their reproductive period further reduced to May to July (Leifsson, 1999). In the more southern extent of its range, the reproductive season of Idotea pelagica would be expected to shift further towards winter.
  • Fecundity
  • Females brood up to 80 eggs for 6-8 weeks (Leifsson, 1999), as with most isopods there is no larval stage and the juveniles appear as the adults, but with 6 pairs of pereopods not 7. Once the eggs hatch, females may then moult and produce a second brood (Healy & O'Neill, 1984).
    Reproduction References Leifsson, 1999, Healy & O'Neill, 1984, Sheader, 1977,
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