Atrina fragilis

Researched ByDr Harvey Tyler-WaltersData Supplied ByMarLIN
Refereed byDr Dan Minchin
Taxonomy
Scientific nameAtrina fragilisCommon nameFan mussel
MCS CodeW1733Recent SynonymsPinna fragilis, Pinna pectinata.
PhylumMolluscaSubphylum
SuperclassClassPelecypoda
SubclassOrderPteroidea
SuborderFamilyPinnacea
GenusAtrinaSpeciesfragilis
Subspecies  
Additional InformationNo text entered
Taxonomy References Howson & Picton, 1997, Tebble, 1976, Woodward, 1985
General Biology
Growth formBivalvedFeeding methodActive suspension feeder
Mobility/MovementTemporary attachment, BurrowerEnvironmental positionInfaunal
Typical food typesNo text enteredHabitAttached
BioturbatorFlexibilityNone (< 10 degrees)
FragilityIntermediateSizeMedium-large(21-50cm)
HeightInsufficient informationGrowth Rateca 3-4 cm/year
Adult dispersal potentialVery limited (<1m)DependencyIndependent
SociabilitySolitary
Toxic/Poisonous?No
Additional InformationAnon (1999c) suggested that growth is relatively slow (c. 3 -4 cm/year), based on annular growth rings in specimens from Valentia Bay, Ireland. Bulter et al. (1993) note that the growth of Pinna bicolor is indeterminate, rapid when small and slow after 2 years of age. Shell margin is easily damaged to produce sharp edges. These edges may cut the feet of bathers (Anon 1999c). Fan mussels rapidly repair the shell (Yonge, 1953). Fan mussel communities have been poorly studied in the UK and information is only available from the Mediterranean, South Australia and the USA. Pseudofaeces results in biodeposits that reduce the variability of nematode meiofauna in Atrina zealandica beds (Warwick et al. 1997). Pinna bicolor hosts a species rich epifauna (Kay & Keough, 1981; Ward & Young 1984). In St Joseph Bay, Florida shells of dead Atrina rigida, predated by the horse conch, provide shelter for crabs, fish and octopus and were used as 'nests' by blennies, clingfish and toadfish (Kuhmann 1997)
Biology References Tebble, 1976, Anonymous, 1999(c), Yonge, 1953, Butler et al., 1993, Ward & Young, 1983, Warwick et al., 1997, Kay & Keough, 1981, Kuhlmann, 1997
Distribution and Habitat
Distribution in Britain & IrelandPredominantly southern and western shores of the UK from North Scotland to the Iberian Peninsula, including the Channel Isles (see additional information below). Recorded at Milford Haven.
Global distributionNorthern UK to Iberian Peninsula and the Adriatic Sea.
Biogeographic rangeNot researchedDepth rangeLWS to 400m
MigratoryNon-migratory / Resident
Distribution Additional InformationDistribution
Specimens occur as solitary individuals or localized patches of small groups of individuals. Records for Ireland were supplied by Julia Nunn and the Centre for Environmental Data and Recording (CEDaR). Records of fan mussel shells, and records before 1950, are more widespread than shown in the above map, which only shows live records after 1950.

Atrina fragilis was recorded in Zostera sp. beds in the Isles of Scilly, however specimens have not been found since the Zostera sp. beds were lost (Turk 1982; Turk & Seaward 1997). This species was more common in scallop areas in the early 1900s. Presumably trawling and dredging of theses formerly populated regions is the reason for the decline of this species (Minchin pers. comm.). Dredging of a Pecten maximus bed off Glengad Head, Ireland, after 1975, removed many live specimens of Atrina fragilis in scallop dredges and the population of fan mussels is thought to have been destroyed by subsequent dredging (Anon 1999c).

The species is known from weak to moderately strong currents, for example in Knightstown, Valentia Island the population is exposed to >2 knots on spring tides (Dan Minchin pers. comm.). Although usually found at full salinities it may be exposed to reduced or variable salinities for brief periods (Dan Minchin pers. comm.).
Substratum preferencesGravel / shingle, Mixed, Muddy gravel, Muddy sand, Mud, Fine clean sand, Sandy mud, Coarse clean sandPhysiographic preferencesOffshore seabed, Ria / Voe, Enclosed coast / Embayment
Biological zoneSublittoral Fringe, Upper Infralittoral, Lower Infralittoral, Upper Circalittoral, Lower CircalittoralWave exposureSheltered, Very Sheltered
Tidal stream strength/Water flowModerately Strong (1-3 kn), Weak (<1 kn)SalinityFull (30-40 psu)
Habitat Additional Information
Distribution References Tebble, 1976, Woodward, 1985, Anonymous, 1999(c), Seaward, 1990, Seaward, 1982, Turk, 1982, Turk & Seaward, 1997, Moore, 2002, Simunovic et al., 2001
Reproduction/Life History
Reproductive typeGonochoristic Developmental mechanismPlanktotrophic
Reproductive SeasonInsufficient informationReproductive LocationInsufficient information
Reproductive frequencyInsufficient information Regeneration potentialNo
Life span11-20 yearsAge at reproductive maturityInsufficient information
Generation timeInsufficient informationFecundityInsufficient information
Egg/propagule sizeInsufficient informationFertilization typeInsufficient information
Larvae/Juveniles
Larval/Juvenile dispersal potential10-100mLarval settlement periodInsufficient information
Duration of larval stageInsufficient information  
Additional InformationAtrina fragilis is assumed to be long lived due to its large size and longevity is expected to be in excess of 10 years (D. Minchin, pers. comm.). Butler et al. (1993) report that the related Mediterranean genus Pinna nobilis may live up to 18 yr. Dispersion is assumed to be possible over large distances due to the pelagic life history. However, Butler et al. (1993) mention evidence for genetic population sub-division in Pinna bicolor within the Gulf of St Vincent in South Australia, which suggests that effective dispersal is lower than expected.
Reproduction References Butler et al., 1993, Butler, 1987, Booth, 1979.