BIOTIC Species Information for Electra pilosa
Researched byDr Harvey Tyler-Walters Data supplied byMarLIN
Refereed byDr Peter J. Hayward
Scientific nameElectra pilosa Common nameA sea mat
MCS CodeY178 Recent SynonymsNone

PhylumBryozoa Subphylum
Superclass ClassGymnolaemata
Subclass OrderCheilostomatida
SuborderMalacostegina FamilyElectridae
GenusElectra Speciespilosa

Additional InformationColonies of Electra pilosa growing on erect substrata (e.g. a hydroid) may continue to grow lengthways once they have used up the available substratum, forming narrow, bilaminar fronds of zooids side by side, once described as Electra verticillata. Colonies growing on small pieces of substratum (e.g. a shell) occasionally enclose the substratum forming an unattached spherical colony, 3-7cm in diameter (Hayward & Ryland, 1998).
Taxonomy References Howson & Picton, 1997, Hayward & Ryland, 1995b, Hayward & Ryland, 1998, Ryland, 1967, Ryland, 1976, Ryland, 1970,
General Biology
Growth formCrustose hard
Feeding methodActive suspension feeder
Mobility/MovementPermanent attachment
Environmental positionEpifaunal
Typical food typesPhytoplankton, algal spores. HabitAttached
BioturbatorNot relevant FlexibilityNone (< 10 degrees)
FragilityFragile SizeSmall-medium(3-10cm)
Height Growth RateSpecific growth rate 0.08 / day
Adult dispersal potential10-100m DependencyIndependent
General Biology Additional InformationGrowth form
Electra pilosa displays a variety of growth forms, such as, stellate patches on flat substrata, cylindrical growths around algae to narrow tufts, and narrow bilaminar fronds or occasionally as spherical masses around small substrata, described earlier (see Ryland, 1967, 1976; and Silén, 1987 for reviews).
The median proximal spine may become greatly elongated in response to overgrowth by colonies of other bryozoans (Stebbing, 1973; Ryland, 1976) or in response to wave related abrasion by algae (Bayer et al., 1997). The extended spine may protect the feeding polypide from physical or mechanical disturbance (Bayer et al., 1997).

Growth rates
Growth rates in bryozoans have been shown to be vary with environmental conditions, especially water flow, food supply, temperature, competition for food and space, and genotype. For example:
  • Best & Thorpe (1986) reported that feeding rate increased with increasing food concentration;
  • Bayer et al. (1994) noted that variation in growth rates between colonies due to genotype was greater than that due to food ration;
  • Okamura (1988) reported that in epiphytic communities, feeding rate increased with increasing flow (from 0.01-0.02 m/sec to 0.1-0.12m/s) but was reduced by competing bryozoan communities (Alcyonidium sp. or Flustrellidra hispida) in slow flow but enhanced by them in fast flow conditions; and
  • bryozoans studied (inc. Electra pilosa) in natural currents in the Menai Strait, fed adequately and maintained growth even in very high current flows (Hermansen, et al., 2001).
  • Although growth rates increased with temperature, zooid size decreased, which may be due to increased metabolic costs at higher temperature (Menon, 1972; Ryland, 1976; Hunter & Hughes, 1994). In the Menai Straits larger zooids are produced in spring at times of peak phytoplankton primary productivity but mean zooid size decreased as temperatures increased in summer (Okamura, 1987 cited in Hunter & Hughes, 1994).
Growth rates of 0.1-0.12 µ /day were reported, irrespective of flow regime, and genotype, while natural population were reported to grow at ca 0.08 µ/ day (Hermansen et al., 2001).

The structure and function of the bryozoan lophophore was reviewed by Ryland (1976), Winston, (1977) and Hayward & Ryland (1998). Best & Thorpe (1994) suggested that intertidal Bryozoa would probably be able to feed on small flagellates, bacteria, algal spores and small pieces of abraded macroalgae.

Allergenic response
Electra pilosa and other bryozoans have been reported to cause dermatitis and occupational eczema in fishermen (Ryland, 1967; Jeanmougin et al., 1987 summary only).
Biology References Hayward & Ryland, 1995b, Hayward & Ryland, 1998, Ryland, 1967, Jeanmougin et al, 1987, Stebbing, 1973, Ryland, 1976, Bayer et al., 1997, Best & Thorpe, 1986, Bayer et al., 1994, Silén, 1987, Hermansen et al., 2001, Okamura, 1988, Ryland, 1977, Menon, 1972, Hunter & Hughes, 1994, Ryland, 1970, Best & Thorpe, 1994, Winston, 1977,
Distribution and Habitat
Distribution in Britain & IrelandCommon on all coasts of the British Isles, although under recorded on parts of the east coast.
Global distributionCommon in all temperate seas.
Biogeographic rangeNot researched Depth rangeIntertidal to at least 50m
MigratoryNon-migratory / Resident   
Distribution Additional InformationElectra pilosa may be found on most substrata, and is part of the epiphytic fauna of macroalgae such as %Fucus serratus% in the intertidal and the stipes or holdfasts of laminarians in the subtidal. Electra pilosa may also be found encrusting the shells of shellfish such as mussels. It is also a common member of the fouling community (Ryland, 1967). The abundance of bryozoans is positively correlated with supply of hard substrata and hence with current strength (Eggleston, 1972b; Ryland, 1976). Similarly, the abundance of Electra pilosa increased with increasing fucoid density and surface area (O'Connor et al., 1979).

Substratum preferencesBedrock
Large to very large boulders
Small boulders
Other species (see additional information)
Artificial (e.g. metal/wood/concrete)
Under boulders
Physiographic preferencesOpen coast
Strait / sound
Ria / Voe
Enclosed coast / Embayment
Biological zoneMid Eulittoral
Lower Eulittoral
Sublittoral Fringe
Upper Infralittoral
Lower Infralittoral
Wave exposureModerately Exposed
Tidal stream strength/Water flowStrong (3-6 kn)
Moderately Strong (1-3 kn)
Weak (<1 kn)
SalinityFull (30-40 psu)
Habitat Preferences Additional Information
Distribution References Hayward & Ryland, 1995b, Hayward & Ryland, 1998, Bruce et al., 1963, Ryland, 1967, Ryland, 1976, Ryland, 1977, Moore, 1973c, Ryland, 1970, O'Connor et al., 1979, Gontar & Denisenko, 1989,
Reproduction/Life History
Reproductive typeBudding
Permanent hermaphrodite
Developmental mechanismPlanktotrophic
Reproductive SeasonAugust to September Reproductive LocationWater column
Reproductive frequencyAnnual episodic Regeneration potential No
Life spanInsufficient information Age at reproductive maturityInsufficient information
Generation time<1 year FecundityUp to ca 30 oocytes
Egg/propagule size121-145 µm Fertilization typeInternal
Larval/Juvenile dispersal potential>10km Larval settlement period
Duration of larval stageSee additional information   
Reproduction Preferences Additional InformationReproduction
Bryozoan colonies are hermaphrodite, however, zooids may be monoecious, dioecious, protandrous or protogynous, depending on species (Hayward & Ryland, 1998). Sperm are shed from pores in the polypide tentacles of male zooids (Hayward & Ryland, 1998). In Electra pilosa maternal lophophores may actively collect sperm (Temkin, 1996). The ovaries produce up to 31 oocytes of 121-145 µm in diameter, which are released into the coelomic cavity. Temkin (1996) has shown recently that fertilization is internal, rather than external as thought previously (see Reed, 1991). Eggs come into contact with sperm (either as aggregates or singly) in the coelomic cavity, fertilization occurring at or near ovulation (Temkin, 1996). Embryos are shed into the water column and develop into planktonic cyphonautes larvae (Ryland, 1976; Reed, 1991; Hayward & Ryland, 1998). Entrainment of released sperm by the tentacles of feeding polypides in bryozoans, may reduce dispersal, resulting in self-fertilization (Temkin, 1996).
Individual zooids may produce up to 31 eggs and potentially the same number of embryos (with a fertilization efficiency of 83-100%) (Temkin, 1994), although Hyman (1959) reported a maximum of 17 eggs being released. However, while each individual zooid is not prolific, the fecundity of the colony is probably directly proportional to the number of functional zooids (Bayer et al., 1994).

Reproductive season
Colonies containing eggs and sperm are present in August and September and cyphonautes larvae are present in the plankton throughout the year (Hayward & Ryland, 1998). Electra pilosa was reported to settle between April and the end of November, with peaks in May/June and July to August (Ryland, 1967).
Bayer et al. (1994) reported that colonies of Electra pilosa maintained in the laboratory died from the inside out, i.e. after several months the central part of the colony generally began to die. They noted that longevity data for Electra pilosa colonies was not available. However, although Electra pilosa colonies could probably survive for several years, it is probably adapted to ephemeral habitats, capable of rapid growth and reproduction of numerous offspring (r-selected).

Bryozoan larvae are probably sensitive to surface contour, chemistry and the proximity of conspecific colonies. However, Hayward & Ryland (1998) suggested that larval behaviour at settlement is only of prime importance to species occupying ephemeral habitats. For example, Electra pilosa larvae tend to orientate themselves with water flow along Fucus serratus fronds (the trend increasing with wave action) (Ryland, 1977), prefer to settle at the distal ends of the fronds and on the concave surfaces of the seaweed (Seed, 1985). (Eggleston, 1972b) demonstrated that the number and abundance of species of bryozoan increased with increased current strength, primarily due to a resultant increase in the availability of stable, hard substrata (Eggleston, 1972b; Ryland, 1976). Ryland (1976) reported that significant settlement in bryozoans was only found near a reservoir of breeding colonies. Ryland (1977) suggested that marine bryozoan larvae tend to settle on the underside of submerged structures or in shaded habitats, possibly due to avoidance of accumulated sediment or competition from algae. However, Electra pilosa larvae have an extended planktonic life and this species is a common member of fouling communities, and occurs on buoys where many other species of bryozoa are unable to colonize (Ryland, 1967). Therefore, Electra pilosa probably exhibits good dispersal and potentially very rapid recruitment.
Reproduction References Hayward & Ryland, 1998, Ryland, 1967, Ryland, 1976, Bayer et al., 1994, Ryland, 1977, Nielsen, 1990, Reed, 1991, Seed, 1985, Ryland, 1970,
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