Biodiversity & Conservation

American oyster - Crassostrea virginica

American oyster

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Distribution map

Crassostrea virginica recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

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Crassostrea virginica is not listed under any importance categories.

Taxonomy icon Taxonomy Taxon English term
Phylum Mollusca Snails, slugs, mussels, cockles, clams & squid
Class Bivalvia Clams, cockles, mussels, oysters, and scallops
Authority (Gmelin, 1791)
Recent synonyms None
Map icon Recorded Distribution in Britain and Ireland Introduced to the south east and south west of England and north Wales.
Habitat information icon Habitat information 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.
Text page icon Description 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.
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 icon Additional information Similar to Crassostrea gigas (Thunberg) but lacks the bold ribs and crenulate shell margin typical of Crassostrea 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.

This review can be cited as follows:

Susie Ballerstedt 2008. Crassostrea virginica. American oyster. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 09/02/2010]. Available from: <http://www.marlin.ac.uk/speciesinformation.php?speciesID=3082>