Date of introduction and origin
Petricola pholadiformis was introduced not later than
1890 (Naylor 1957) and found in the River Crouch, Essex
(International Council for the Exploration of the Sea; 1972, Tebble
1976). The species is native to the USA and was introduced from
Method of introduction
It was an associated unintentional introduction with the
American oysterCrassostrea virginica (Rosenthal
Reasons for success
Rate of spread and methods involved
Rosenthal (1980) indicates that this species has colonised
several northern European countries by means of it pelagic larvae.
It also possibly spread in drift wood.
It is established along south and east coasts of England from
Lyme Regis, Dorset, to the Humber, Humberside (Duval 1963; J. Light
& I. Killeen pers. comm.), where it is found living in clay,
peat or soft rock shores. It is most common off Essex and the
Thames estuary e.g. the River Medway (see Bamber 1985). European
populations occur from southern Norway to the Mediterranean and
Black Seas (Tebble 1976).
Factors likely to influence spread and distribution
Its spread is influenced by ocean currents as it disperses
through larval transport.
Effects on the environment
In Belgium and The Netherlands it has almost completely
replaced the native species Barnea candida (International
Council for the Exploration of the Sea; 1972). In Britain, however,
there is no documentary evidence for its having displaced native
piddocks (J. Light & I. Killeen pers. comm.).
Effects on commercial interests
Control methods used and effectiveness
Petricola is remarkably similar to Barnea
candida (an indigenous British species).
Bamber, R.N. 1985. Coarse substrate benthos of Kingsnorth
outfall lagoon, with observations on Petricola
pholadiformis Lamarck. Central Electricity Research
Laboratories Report TPRD/L 2759/N84.
Duval, D.M. 1963. The biology of Petricola
pholadiformis Lamarck (Lamellibranchiata: Petricolidae).
Proceedings of the Malacological Society. 35:
Hayward, P.J., & Ryland, J.S. eds. 1990. The
marine fauna of the British Isles and north-west Europe. 2
vols. Oxford, Clarendon Press.
International Council for the Exploration of the Sea. 1972.
Report of the working group on the introduction of
non-indigenous marine organisms. International Council for the
Exploration of the Sea.
Naylor, E. 1957. Immigrant marine animals in Great Britain.
New Scientist, 2: 21-53.
Rosenthal, H. 1980. Implications of transplantations to
aquaculture and ecosystems. Marine Fisheries Review,
Tebble, N. 1976. British bivalve seashells. A handbook for
identification. 2nd ed. Edinburgh, HMSO, for Royal Scottish