American oyster (Crassostrea virginica)

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



Crassostrea virginica is elongate and broadly oval reaching up to 18 cm in length. The left valve is convex and sculptured with concentric ridges and lines whilst the right valve tends to be flat. There are a few irregular radiating ribs on the left valve which do not normally meet or indent the margin. The shell margin is smooth, and the beaks and umbones are not prominent. The inner surface is pearly white or bluish-white, and the outer surface is deep purple or reddish brown in colour. The adductor muscle scar is near the posterior margin.

Recorded distribution in Britain and Ireland

Introduced to the south east and south west of England and north Wales.

Global distribution

Distributed along the coast of North America from St Lawrence to the Gulf of Mexico and Panama.


This species can be found on the lower shore and shallow sublittoral. It is a prolific species in its native home and can be found on any hard surface, often becoming long and distorted when overcrowded. It is tolerant to very low salinity.

Depth range


Identifying features

  • Shell can grow up to 18 cm in length.
  • Left valve is convex and sculptured.
  • Right valve is flat.
  • Shell margin is smooth.
  • Outer shell surface is deep purple or reddish brown.

Additional information

Similar to Magallana gigas (Thunberg) but lacks the bold ribs and crenulate shell margin typical of Magallana gigas. Both Crepidula fornicata and Urosalpinx cinera were introduced with Crassostrea virginica (Yonge & Thompson, 1976). Crepidula fornicata out-competes the American oyster for space, whereas Urosalpinx cinerea is a common predator of Crassostrea virginica. However, if the shell of the oyster is over 0.4 cm thick at the point of attack then Urosalpinx cinerea will be unsuccessful (Wilbur, 1988).

Crassostrea virginica reproduces externally with both eggs and sperm being discharged through the exhalent siphon. Over 100 million eggs may be liberated from a single female. Spawning of one individual also induces spawning in the surrounding population, therefore maximizing gamete interaction. Interestingly, spawning is temperature dependent; populations in cool temperate waters only spawn at 17°C, while populations in slightly warmer waters spawn at 20°C and sub-tropical populations spawn at 25°C. When transplanted to a different habitat individuals will not spawn, which together with competition and predation pressure from Crepidula fornicata and Urosalpinx cinerea respectivily, are likely explanations for the unsuccessful establishment of Crassostrea virginica.

Listed by

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  1. Beaumont, A.R., Newman, P.B., Mills, D.K., Waldock, M.J., Miller, D. & Waite, M.E., 1989. Sandy-substrate microcosm studies on tributyl tin (TBT) toxicity to marine organisms. Scientia Marina, 53, 737-743.

  2. Bowden, J. & Heppell, D., 1966. Revised List of British Mollusca 1. Introduction; Nuculacea-Ostreacea. Journal of Conchology, 26, 99-124.

  3. Hayward, P.J. & Ryland, J.S. (ed.) 1995b. Handbook of the marine fauna of North-West Europe. Oxford: Oxford University Press.

  4. Seaward, D.R., 1990. Distribution of marine molluscs of north west Europe. Peterborough: Nature Conservancy Council.

  5. Tebble, N., 1976. British Bivalve Seashells. A Handbook for Identification, 2nd ed. Edinburgh: British Museum (Natural History), Her Majesty's Stationary Office.

  6. Wilbur, K.M., 1988. The Mollusca. Volume II: Form and Function. London: Academic Press Inc. Ltd.,

  7. Yonge, C.M. & Thompson, T.E., 1976. Living Marine Molluscs London: Collins.

  8. Yonge, C.M., 1960. Oysters. London: Collins.


  1. Conchological Society of Great Britain & Ireland, 2018. Mollusc (marine) records for Great Britain and Ireland. Occurrence dataset: accessed via on 2018-09-25.

  2. NBN (National Biodiversity Network) Atlas. Available from:

  3. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. Accessed: 2024-07-21


This review can be cited as:

Ballerstedt, S. 2008. Crassostrea virginica American oyster. 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 21-07-2024]. Available from:

Last Updated: 08/07/2008