BIOTIC Species Information for Helcion pellucidum
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Researched byDr Harvey Tyler-Walters Data supplied byMarLIN
Refereed byDr David McGrath
Taxonomy
Scientific nameHelcion pellucidum Common nameBlue-rayed limpet
MCS CodeW234 Recent SynonymsPatina pellucida, Patina laevis, Helcion laevis

PhylumMollusca Subphylum
Superclass ClassGastropoda
SubclassProsobranchia OrderPatellogastropoda
Suborder FamilyPattelidae
GenusHelcion Speciespellucidum
Subspecies   

Additional InformationSpecimens found in cavities in holdfasts develop into the laevis form (Helcion pellucidum var. laevis). The laevis form has a taller, more robust opaque shell, ledged in profile, with blue rays that alternate with reddish brown rays. The most noticeable ledge of the shell indicates the size at which the individual enters the holdfast. Weber et al. (1997) suggested that Helcion pellucidum was genetically distinct from its South African con-geners and may have arisen independently. Recent studies of morphological features (Ridgeway et al., 1998) and molecular characteristics (Koufopanou et al., 1999) suggest that Helcion pelludicum belongs to the genus Patella.
Taxonomy References Fish & Fish, 1996, Hayward & Ryland, 1995b, Weber et al., 1997, Ridgeway et al., 1998, Fretter & Graham, 1994, Koufopanou, 1999,
General Biology
Growth formConical
Feeding methodHerbivore
Mobility/MovementTemporary attachment
Crawler
Environmental positionEpifaunal
Typical food types%Laminaria hyperborea%, %Laminaria digitata%, %Alaria esculenta%, %Sacchoriza polyschides%, %Fucus serratus%, and when young %Himanthalia elongata% and %Mastocarpus stellatus%. HabitFree living
BioturbatorNot relevant FlexibilityNone (< 10 degrees)
FragilityRobust SizeSmall(1-2cm)
Height Growth Rate1-2 mm/month
Adult dispersal potentialVery limited (<1m) DependencyIndependent
SociabilitySolitary
Toxic/Poisonous?No
General Biology Additional InformationGrowth is rapid in summer, autumn and winter but slow in winter. Population studies suggest that few individuals survive to their second year (Fretter & Graham, 1976; Graham & Fretter, 1947). Vahl (1971) noted growth irregularities or 'checks' in the shell of specimens from Norway, which he suggested were caused by the interrupted growth of the mantle edge when the adult was retracted in response to severe wave action during heavy storms.

Adults can recolonize vacant fronds (McGrath, 1997), perhaps via the surface of the substratum or by mucus rafting, and if dislodged adults can right themselves and be carried to neighbouring plants by currents by secreting a mucus 'sail' (Vahl ,1983).

Kain & Svendsen (1969) provide pictures of Helcion pellucidum on blades of Laminaria hyperborea together with the cavities grazed in the fronds and in holdfasts. Kain & Svendsen (1969) noted that in Norwegian populations severe grazing by Helcion pellucidum may result in perforation of blades by autumn (before new blades develop) and in some cases grazing where the blade and stipe meet may 'cut off' the blade.
Biology References Fish & Fish, 1996, Fretter & Graham, 1976, Graham & Fretter, 1947, McGrath, 1992, McGrath, 1997, Vahl, 1983, Fretter & Graham, 1994, Kain & Svendsen, 1969, Vahl, 1971,
Distribution and Habitat
Distribution in Britain & IrelandRecorded on all coasts of Britain and Ireland, except the coast surrounding the Wash.
Global distributionOccurs in Iceland and from north Norway to south Portugal. It is found on the west coasts of Denmark, and Sweden south to Oresund. However it is absent from the Baltic sea and the east coasts of Denmark, Belgium and Holland.
Biogeographic rangeNot researched Depth rangeca +1 - 25 m
MigratoryNon-migratory / Resident   
Distribution Additional InformationStudies in south east Ireland demonstrated that the distribution of Helcion pellucidum on the shore depends on its size and age. McGrath (1992) noted that spat settled with a larval shell attached of ca 0.66 mm. Newly settled spat have a preference for lower shore Lithothamnia (encrusting coralline algae) reaching densities as high as 400 per sq. dm in February. As they grow juveniles (up to 1.8 mm) migrate to Mastocarpus stellatus. The juveniles recruit to Laminarians at about 1.8 mm but are found mainly at the tips of the fronds. Juveniles up to 3 mm may also be found on the receptacles of %Himanthalia elongata%. Dense populations may be found on Fucus serratus, Alaria esculenta, Palmaria palmata and Halidrys siliquosa (McGrath, 1992).

Adults show a seasonal migration on Laminaria hyperborea, migrating down to the stipe before the old blade tissue is discarded in spring to early summer. Larger individuals prefer the lower wave exposure of deeper water (Warburton 1976).

Approximately one third of the population examined by Graham & Fretter (1947) were the laevis form. However, Kain & Svendsen (1969) did not find any specimens in Laminarian holdfasts in Norwegian populations and the laevis form may be absent in Norway.

Substratum preferencesAlgae
Physiographic preferencesOpen coast
Strait / sound
Sealoch
Biological zoneLower Eulittoral
Sublittoral Fringe
Upper Infralittoral
Wave exposureExposed
Moderately Exposed
Tidal stream strength/Water flowModerately Strong (1-3 kn)
SalinityFull (30-40 psu)
Habitat Preferences Additional InformationNone
Distribution References Hayward & Ryland, 1995b, Fretter & Graham, 1976, Graham & Fretter, 1947, McGrath, 1992, Warburton, 1976, Ebling et al., 1948, Seaward, 1990, Seaward, 1982, Kain & Svendsen, 1969, Vahl, 1971, MBA, 1957,
Reproduction/Life History
Reproductive typeGonochoristic
Developmental mechanismPlanktotrophic
Reproductive SeasonAll year with a peak in spring Reproductive LocationAs adult
Reproductive frequencyAnnual protracted Regeneration potential No
Life span1-2 years Age at reproductive maturity<1 year
Generation time<1 year FecundityInsufficient information
Egg/propagule sizeCa 0.16 mm diameter Fertilization typeExternal
Larvae/Juveniles
Larval/Juvenile dispersal potential10-100m Larval settlement periodInsufficient information
Duration of larval stage11-30 days   
Reproduction Preferences Additional InformationFew individuals survive into their second years. Most specimens >1 year old are found in holdfasts as the laevis form. Breeding occurs throughout the year with a peak in spring. Fertilization is external and eggs are shed singly. The eggs are greenish, ca 0.16 mm across and covered with a gelatinous coat giving an overall diameter of ca 0.32 mm (Fretter & Graham, 1976; Lebour, 1937). Eggs hatch into a 200 micrometer tall trochophore that develops into a 160-180 micrometer veliger larva (Lebour, 1937). Fretter & Graham (1947) state that planktonic life is 'a few weeks'. There is little information on dispersal range, however, 10-100m is assumed given the depth of adult distribution and its settlement on lower shore at least. McGrath (1992) examined recruitment in south east Ireland and reported that newly settled spat have a preference for lower shore Lithothamnia (encrusting corallines). As they grow juveniles (up to 1.8 mm) migrate to Mastocarpus stellatus. The juveniles recruit to Laminarians at about 1.8 mm but are found mainly at the tips of the fronds. Juveniles up to 3 mm may also be found on the receptacles of Himanthalia elongata. McGrath (1992) suggested that larvae settle on Lithothamina and migrate to Mastocarpus stellatus as they grow and finally to Laminaria sp. via Himanthalia elongata.
Reproduction References Fish & Fish, 1996, Fretter & Graham, 1976, Graham & Fretter, 1947, McGrath, 1992, Fretter & Graham, 1994, Lebour, 1937,
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