The Marine Life Information Network

Information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles


Blue-rayed limpet (Patella pellucida)

Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help



Smooth, translucent brownish yellow - horn coloured shell, up to 2 cm in length and much smaller than the common limpet (Patella spp.). Oval in outline in the shape of a depressed cone with the apex at the anterior end. The shell is overlayed by 2-8, characteristic, broken (dashed) blue-green rays, although these are absent from the juvenile shell until they reach 1.1mm in length.

Recorded distribution in Britain and Ireland

Recorded on all coasts of Britain and Ireland, except the coast surrounding the Wash.

Global distribution

Occurs 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.


Found on the blade of laminarians or fronds of Fucus serratus, Mastocarpus stellatus or Himanthalia elongata from the lower eulittoral to a depth of ca 27 m. Newly settled juveniles found on encrusting coralline algae in wave exposed conditions in the lower eulittoral. It prefers areas of considerable water flow and is not normally found in areas of low flow, siltation or freshwater influence.

Depth range

ca +1 m - ca 25 m

Identifying features

  • Small, translucent, brownish yellow - horn coloured depressed shell.
  • Characteristic dashed blue rays radiating from apex of shell.
  • Foot and body cream but browner on head and edge of foot
  • No pallial gills on edge of mantle at front of body

Additional information

Weber et al. (1997) suggested that Patella pellucida (as Helcion pellucidum) was genetically distinct from its South African con-geners and may have arisen independently. Studies of morphological features (Ridgeway et al., 1998) and molecular characteristics (Koufopanou et al., 1999) suggested that Helcion pelludicum belonged to the genus Patella and the species name was restored to Patella pellucida (Linnaeus, 1758).

Specimens found in cavities in holdfasts develop into the laevis form (Patella pellucida 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.


Listed by

- none -

Biology review


AuthorityLinnaeus, 1758
Recent SynonymsPatina laevis Patina pellucida Linnaeus, 1758Helcion laevis Helcion pellucidum


Typical abundanceModerate density
Male size range3 - 12mm
Male size at maturity5mm
Female size range5mm
Female size at maturity
Growth form
Growth rate1-2mm/month
Body flexibilityLow (10-45 degrees)
MobilityCrawler / Walker, Creeper
Characteristic feeding methodGrazer
Diet/food sourceHerbivore
Typically feeds on%Laminaria hyperborea%, %Laminaria digitata%, %Alaria esculenta%, %Saccorhiza polyschides%, %Fucus serratus%, and when young %Himanthalia elongata% and %Mastocarpus stellatus%.
SociabilityNo information
Environmental positionEpifaunal
DependencyNot relevant.
SupportsNot relevant
Is the species harmful?No

No text entered

Biology information

Growth 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 Patella pellucida 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 Patella pellucida 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.

Habitat preferences

Physiographic preferencesOpen coast, Strait / sound, Sea loch / Sea lough, Open coast, Sea loch / Sea lough, Strait / sound
Biological zone preferencesLower eulittoral, Sublittoral fringe, Upper infralittoral, Lower eulittoral, Sublittoral fringe, Upper infralittoral
Substratum / habitat preferencesMacroalgae, Macroalgae
Tidal strength preferencesModerately Strong 1 to 3 knots (0.5-1.5 m/sec.), Moderately Strong 1 to 3 knots (0.5-1.5 m/sec.)
Wave exposure preferencesExposed, Moderately exposed, Exposed, Moderately exposed
Salinity preferencesFull (30-40 psu), Full (30-40 psu)
Depth rangeca +1 m - ca 25 m
Other preferencesOccurs at 15 psu in Norway.
Migration Pattern

Habitat Information

Studies in south-east Ireland demonstrated that the distribution of Patella pellucida on the shore depended 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.

Life history

Adult characteristics

Reproductive typeGonochoristic (dioecious)
Reproductive frequency Annual protracted
Fecundity (number of eggs)No information
Generation time<1 year
Age at maturitycirca 6 months (5mm in size)
SeasonInsufficient information
Life span1-2 years

Larval characteristics

Larval/propagule typeVeliger
Larval/juvenile development Planktotrophic
Duration of larval stage11-30 days
Larval dispersal potential 10 -100 m
Larval settlement periodInsufficient information

Life history information

Few 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 3mm 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.

Sensitivity reviewHow is sensitivity assessed?

Physical pressures

High Very high Low Moderate
Loss of the substratum, this species food plants, will involve removal of the adults themselves. Adults may be lost with plants during storms or swept off the fronds. However, McGrath (1997) demonstrated that Patella pellucida can rapidly recolonize available plants with as little as three days from adjacent plants. It is likely that recolonization from adjacent populations would be fairly rapid.
Intermediate Very high Low Low
Smothering by 5 cm of material is unlikely to affect adults on the fronds of kelps. The laevis form in holdfasts may be more intolerant. Similarly, the typical food species have a low intolerance to smothering. Smothering is likely to interfere with the settlement of larvae which, if lost, may significantly reduce the population of this near annual species.
Intermediate Very high Low Low
Patella pellucida is not found in areas of low water flow and siltation. Increased levels of suspended sediment are likely to interfere with feeding. However, its typical food species has a low intolerance to siltation. Larvae may be more intolerant at settlement which, if lost, may significantly reduce the population of this near annual species.
No information
Intermediate Very high Low Low
Subtidal adults are unlikely to be affected except at extreme low tides. Increased desiccation is likely to affect the juvenile stages found in the lower eulittoral and adults on Fucus serratus. These are likely to be intolerant of an increased desiccation equivalent to moving from the lower to mid eulittoral for a year. Although the limpet can close tightly to macroalgae and creates pits and scars like its littoral co-familial Patella spp. the typical food plants (its substratum) are likely to be intolerant of increased desiccation and increased competition from other algal species more tolerant of desiccation. However, it is likely that recolonization from neighbouring populations would be rapid once the original conditions returned.
Low Immediate Not sensitive Low
Decreased emergence is likely to increase the distribution of kelps up the shore and therefore Patella pellucida. Increasing emergence may reduce the upper extent of the kelp species, however, Patella pellucida could move to alternative food species such as Fucus serratus.
No information
Intermediate Very high Low Moderate
The distribution of Patella pellucida is dependent on water flow rate. Studies in Lough Ine rapids (Ebling et al. 1948) found that Patella pellucida was very scarce on Saccorhiza polyschides in weak currents, plentiful in moderately strong currents (0.6-1.5 m/s) and scarce in strong currents (>1.5 m/s). Warburton (1976) demonstrated that large individuals could resist currents up to 0.9-1.3 m/s and smaller individuals resisted stronger currents before being swept off the fronds of kelp. Adults aligned themselves with the current flow above 0.5m/s and currents above 1.0- 1.4 m/s interfered with feeding and normal behaviour. Larger individuals are found in higher abundance in deeper water although Fretter & Graham (1994) suggested that larger individuals migrate to holdfasts. Therefore, it is likely that this species would be intolerant of either a decrease or increase in the water flow rate, equivalent to the benchmark, outside its habitat preferences.
No information
Intermediate Very high Low
The wide distribution of this species suggests that it is tolerant of a wide range of temperatures. However, no information on the temperature tolerance of this species was found. It is likely that its food species are intolerant of increases in temperature consistent with the benchmark, so an intermediate intolerance has been recorded.
No information
Intermediate Very high Low
Turbidity resulting from suspended sediment may interfere with feeding as above. Reduced light penetration will reduce the extent of the food species (kelps).
No information
Low Immediate Not sensitive
This species prefers exposed to moderately exposed shores and it is likely to be intolerant of a change in wave exposure. The available food kelp species will change with exposure and increasing exposure may result in loss of older plants , especially those whose holdfasts had been weakened by Patella pellucida feeding, and adults of this species.
No information
Tolerant Not relevant Not sensitive Moderate
There is no known effect of noise on this species or its prey species.
Tolerant Not relevant Not sensitive Moderate
Although this species probably displays phototaxis there is no evidence of disturbance due to visual stimuli.
Intermediate Very high Low Low
The shell in this species is relatively thin when compared with other limpets. Abrasion at the benchmark level is likely to knock some individuals off its food plant and crush or fracture the shell of others. A passing scallop dredge is likely to remove its substratum, i.e. kelps resulting in substratum loss as above. Therefore, a single scallop dredge will remove or damage a proportion of the kelp canopy and hence a proportion of Patella pellucida. Therefore, intolerance has been assessed as intermediate.
Tolerant Not relevant Not sensitive Moderate
It is presumed that individuals of this species are periodically swept off their food plant. Although some individuals may be lost to deep water, Patella pellucida can re-orientate itself (as it will land upside down, foot upper most) and move to other plants using a mucus 'sail', secreted by the glands of the foot (Vahl 1983). McGrath (1997) demonstrated that plants cleared of Patella pellucida are rapidly recolonized by adults.

Chemical pressures

Intermediate Very high Low Low
Gastropod molluscs are known to be sensitive to endocrine disruption from synthetic chemicals such as tri-butyl tin. However no information on the specific effects of tri-butyl tin on Patella pellucida was found. Hoare & Hiscock (1974) reported that Patella pellucida was excluded form Amlwch Bay, Anglesey by the presence of acidified, halogenated effluent; only eight specimens being found in Amlwch harbour where the silt levels probably reduced the toxicity of chlorine. Patella pellucida probably has an intermediate intolerance to, at least, this form of pollution.
Heavy metal contamination
No information No information No information Not relevant
Bryan (1984) suggested that gastropods are rather tolerant of heavy metals. Crompton (1997) states that the following concentrations of heavy metals have caused mortalities in gastropods after 4-14days (short term); Cu (0.01-0.1 mg/l), Pb (0.1-1mg/l) , Zn (1-10mg/l), Cr and Ni (10-100mg/l). However, no data for this species was found.
Hydrocarbon contamination
No information No information No information Not relevant
Radionuclide contamination
No information No information No information Not relevant
Changes in nutrient levels
Intermediate Very high Low
Increased nutrients are likely to increase epiphyte and food plant growth, potentially increasing the availability of food for Patella pellucida. However, significant increases in nutrient levels (eutrophication), resulting in excessive growth of epiphytes and phytoplankton may have a detrimental effect on this species food plants and, therefore the population of Patella pellucida.
Intermediate Very high Low Low
Patella pellucida is found in full salinity but not in areas of freshwater influence. Juveniles settle on the lower eulittoral and are likely to be subject to freshwater runoff and rainfall at low tide. However, adults are primarily subtidal and likely to be intolerant of long term reduction in salinity outlined in the benchmark.
No information
Intermediate Very high Low
Oxygen concentrations at the level of the benchmark thought to likely to cause effects on marine organisms. In areas of exposure and moderately strong current flow it is unlikely to experience low oxygen levels. Therefore, it is likely to be intolerant of any spillage or activity that reduced the dissolved oxygen concentration to the level of the benchmark

Biological pressures

No information No information No information Not relevant
No microbial pathogens were reported in the literature.
Not relevant Not relevant Not relevant Not relevant
No known alien or non-native species compete with Patella pellucida.
Not relevant Not relevant Not relevant Not relevant
This species is not subject to extraction.
High Very high Low Moderate
Kelp species are harvested in Scotland, Isle of Man and Ireland. Extraction of kelp is equivalent to removal of substratum (see above) in Patella pellucida.

Additional information

Importance review


- no data -



Importance information

Patella pellucida is an important and characteristic herbivore on Laminarians (kelps). It forms distinct pits in the surface of the blade or stipe. The laevis form feeds within the holdfast creating distinct cavities. Photographic images of Patella pellucida on Laminaria hyperborea are shown in Kain & Svendsen (1969). Its feeding, especially in the holdfast weakens the plant and is associated with the loss of adult plants from the kelp forest due to wave or storm action.


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This review can be cited as:

Tyler-Walters, H. 2008. Patella pellucida Blue-rayed limpet. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 28-03-2023]. Available from:

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Last Updated: 08/05/2008