BIOTIC Species Information for Clavelina lepadiformis
Researched byKaren Riley Data supplied byMarLIN
Refereed byDr Xavier Turon
Scientific nameClavelina lepadiformis Common nameLight bulb sea squirt
MCS CodeZD6 Recent SynonymsNone

PhylumChordata SubphylumTunicata
Superclass ClassAscidiacea
Subclass OrderEnterogona
SuborderAplousobranchiata FamilyClavelinidae
GenusClavelina Specieslepadiformis

Additional InformationThe light bulb sea squirt attaches itself to rocks, stones and seaweed in the sublittoral, down to a depth of about 50 m. Individual zooids are small in spring growing to full size by about the end of May in Britain.
Taxonomy References Howson & Picton, 1997, Knight-Jones & Ryland, 1995, Fish & Fish, 1996, Picton & Costello, 1998,
General Biology
Growth formCylindrical
Feeding methodActive suspension feeder
Mobility/MovementPermanent attachment
Environmental positionEpibenthic
Typical food typesSuspended detritus and plankton HabitAttached
BioturbatorNot relevant FlexibilityLow (10-45 degrees)
FragilityFragile SizeSmall(1-2cm)
HeightUp to 2 cm. Growth RateInsufficient information
Adult dispersal potentialNone DependencyIndependent
General Biology Additional Information
  • The light bulb sea squirt grows to a maximum height of 20 mm (Fish & Fish, 1996; Picton, 1997).
  • Colonies grow rapidly in spring and are full size after about two months (K. Hiscock, pers. comm.).
  • The growth rate for settled specimens of Clavelina lepadiformis was found to be high (Tursi et al., 1977), although measures of growth rate were not found.
  • Clavelina lepadiformis is an active suspension feeder, feeding on suspended detritus and plankton present in water passing through the branchial basket (Fish & Fish, 1996). It actively pumps water and can therefore thrive in very still conditions. The structure of the branchial sac for Clavelina lepadiformis is in its simplest form; the gill sheet is formed by a single screen with slits (Fiala-Medioni, 1978). Fiala-Medioni (1974) showed that filtration efficiency decreased with an increase in simplicity of this structure.
  • The zooids of Clavelina lepadiformis are seldom fouled, other than at the base, either because of possible chemical defences or because of the delicate texture of its tunic (Teo & Ryland, 1994).
  • Predators include bottom-feeding fish, carnivorous gastropods and starfish (Millar, 1970). Flatworms are also predators, Prostheceraeus moseleyi being a significant predator of Clavelina lepadiformis is the Mediterranean (X. Turon, pers. comm.).
A study by de Caralt et al. (2002) revealed significant differences in certain aspects of the biology of Clavelina lepadiformis between harbour and open rocky littoral populations in the Mediterranean. Although no morphological differences were found, the abundance in the harbour populations were an order of magnitude higher than at the open littoral population. Furthermore, the harbour population did not experience aestivation (a period of inactivity and reduced metabolic activity), unlike the rocky littoral population, and reproduction also varied greatly. The littoral population only produced larvae for 2-3 months over winter and only had one gonadal cycle per year. By contrast, larvae were present in the harbour population from November to June with several gonadal cycles within this time. They concluded that there was marked ecotypic variation between populations of both habitat types and that the harbour population showed more opportunistic traits (Caralt et al., 2002).
Biology References Fish & Fish, 1996, Millar, 1970, Teo & Ryland, 1995, Teo & Ryland, 1994, Steffan, 1991, Fiala-Medioni, 1978, Tursi et al., 1977, Picton & Costello, 1998, De Caralt et al., 2002, Tarjuelo et al., 2002,
Distribution and Habitat
Distribution in Britain & IrelandClavelina lepadiformis occurs around most coasts of Britain and Ireland.
Global distributionIts distribution extends from southern Norway to the Mediterranean.
Biogeographic rangeNot researched Depth rangeSublittoral to 50 m
MigratoryNon-migratory / Resident   
Distribution Additional Information
  • The species is absent in the Bristol Channel, between Morecambe Bay and Colwyn Bay on the west coast of England, between the Firth of Forth and Newcastle upon Tyne, and the Humber Estuary and Dover on the east coast of Britain. It also has a variable abundance in Ireland.
  • Clavelina lepadiformis is a very common shallow water sea squirt that is usually found on vertical rock faces and on the sides of boulders, to about 50 m depth down (Picton, 1997; Berrill, 1950). It is also found on shells, stones and seaweeds (Picton, 1997), is a typical species of harbour areas, commonly found growing on artificial surfaces.
  • Naranjo et al. (1996) found that the light bulb sea squirt preferred light, shallow environments and was tolerant of salinities as low as 14 psu (Fish & Fish, 1996). It occurs in a wide range of exposure, but is most abundant in moderately exposed sites in the infralittoral zone (Picton, 1997).
  • Naranjo et al. (1996) found that the species was dominant in a low rate of water renewal, excess silting and high suspended solid concentrations, although the species also occurred in other more wave exposed sites.
  • In a study comparing Mediterranean and Atlantic populations of Clavelina lepadiformis in interior (harbours, marinas and fjords) and exterior (open rocky littoral) areas, Turon et al. (2003) found strong evidence that the interior Mediterranean clade (group of organisms sharing the same common ancestry) originated from the Atlantic clade. The Atlantic forms were not found to be divided between interior and exterior clades (Turon et al., 2003).

Substratum preferencesArtificial (e.g. metal/wood/concrete)
Large to very large boulders
Small boulders
Physiographic preferencesOpen coast
Offshore seabed
Strait / sound
Enclosed coast / Embayment
Biological zoneSublittoral Fringe
Upper Infralittoral
Lower Infralittoral
Wave exposureVery Exposed
Moderately Exposed
Very Sheltered
Extremely Sheltered
Tidal stream strength/Water flowSee additional information
Insufficient information
SalinityFull (30-40 psu)
Variable (18-40 psu)
Habitat Preferences Additional Information
Distribution References Fish & Fish, 1996, Berril, 1950, Naranjo et al., 1996, Picton & Costello, 1998, De Caralt et al., 2002, Turon et al., 2003,
Reproduction/Life History
Reproductive typePermanent hermaphrodite
Developmental mechanismOvoviviparous
Reproductive SeasonJune to September Reproductive LocationAs adult
Reproductive frequencyAnnual protracted Regeneration potential No
Life span1-2 years Age at reproductive maturity<1 year
Generation time<1 year Fecundityca 50-60 embryos
Egg/propagule size Fertilization typeInternal
Larval/Juvenile dispersal potential100-1000m Larval settlement periodLate summer
Duration of larval stage2-10 days   
Reproduction Preferences Additional InformationSea squirts are permanent hermaphrodites that undergo both sexual and asexual reproduction.

Sexual Reproduction:
  • Fish & Fish (1996) state that it is not easy to determine the age of ascidians, particularly that of colonial forms but that the lifetime is probably around one or two years. Each zooid reproduces sexually once, with the production of eggs possibly going on for weeks or months (Berrill, 1975). Breeding tends occur during June to September in temperate and cold seas (Picton, 1997; Millar, 1970), but in tropical waters it may continue throughout the year (Millar, 1970). In the Mediterranean, the breeding season is winter/spring (X. Turon, pers. comm.).
  • Fertilisation takes place internally, in the atrium, where development into the tadpole larvae stage also takes place (Fish & Fish, 1996; Berrill, 1950). This process is most likely to occur by cross-fertilization. Brunetti (1987) recorded up to about 50 embryos present in the atrium at one time whereas Tarjuelo & Turon (2004) gave an estimate of 66 embryos.
  • Clavelina lepadiformis brood a large number of small undifferentiated larvae (Tarjuelo & Turon, 2004).
  • After release, the larvae are free-swimming for about three hours (Fish & Fish, 1996; Brunetti, 1987). After this time the larvae settle on suitable substratum and metamorphosis into an adult sea squirt takes place. Development of the oozoid takes up to 3 days, and after 2-3 months of post-developmental growth they become sexually mature (Berrill, 1950).
Asexual reproduction:
  • Clavelina lepadiformis undergoes stolonic asexual budding. At the end of the sexual breeding season, towards the end of the summer, zooids disappear or are resorbed. Over the winter period the colony survives as 'winter buds' from which new zooids develop in spring (Berrill, 1950; Fish & Fish, 1996; Picton, 1997). In the winter months, when the zooids undergo de-differentiation, the resulting cylindrical bodies of many species of Clavelinidae are often found on rocky shores (Millar, 1970). In the Mediterranean the species reproduces in winter/spring and aestivates (aestivation is a period of inactivity / reduced metabolic activity) in summer (X. Turon, pers. comm.).
Reproduction References Fish & Fish, 1996, Millar, 1970, Berril, 1975, Berril, 1950, Brunetti, 1987, Picton & Costello, 1998, Tarjuelo & Turon, 2004,
About MarLIN | Contact, Enquiries & Feedback | Terms & Conditions | Funding | Glossary | Accessibility | Privacy | Sponsorship

Creative Commons License BIOTIC (Biological Traits Information Catalogue) by MarLIN (Marine Life Information Network) is licensed under a Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales License. Permissions beyond the scope of this license are available at Note that images and other media featured on this page are each governed by their own terms and conditions and they may or may not be available for reuse. Based on a work at