Animal Diversity Web

Geographic Range

Gulf of St. Lawrence to the Gulf of Mexico and the West Indies. It was introduced to San Francisco Bay but did not survive.

• Biogeographic Regions
• nearctic
  • native
• neotropical
  • native
• atlantic ocean
  • native

Habitat

Although water temperature affects growth rate, it appears to be irrelevant in site selection. Oysters inhabit areas of fairly constant turbidity and salinity. The oyster is eurytherma,l or able to withstand a wide range of temperatures including freezing temperatures.

• Aquatic Biomes
• reef
• coastal

Physical Description

The Eastern oyster is relatively large, growing up to 10 cm. in length. It is normally somewhat pear-shaped in outline, but members of this species vary greatly in size and shape. The shell is dirty gray externally and white internally, except for the muscle scar, which is deep purple.

• Other Physical Features
• ectothermic
• bilateral symmetry

Reproduction

Reproductive organs can be readily observed only during the breeding season. There is no reproductive activity during the winter. Sexual maturity is a function of size rather than age. The first spawning usually occurs when the oyster is 2 years of age. Fertilization occurs when huge numbers of sperm sperm and eggs are expelled from the male or female and meet in the water.

Behavior

Oysters usually colonize in beds. Competition for space is a most important source of mortality. Uncrowded, oysters can live to be 20 years old. The beds are a permanent social structure unless they are separated physically and forcefully. Otherwise, the oysters will re-congregate if they are capable.

Food Habits

After spawning in early spring, the oyster loses a great deal of weight. This event usually coincides with the spring bloom of phytoplankton, their primary food source. Feeding is dependent upon water temperature; more food is consumed at higher temperatures than at lower.

Economic Importance for Humans: Positive

Oyster cultch or oyster spat is fairly valuable to jewelry trade, though it is rather abundant, due to the large numbers of existing oysters and their relatively high rate of reproductive success. Certain lime or cement coatings are enhaced by use of the cultch. Some Eastern oysters produce pearls as well. Oyster meat is also smoked and canned as a food.

Economic Importance for Humans: Negative

A major problem caused by the oyster is fouling, or attachment, often to boats.

Conservation Status

Oyster health is highly contingent upon water quality. Chemical contamination is widespread and detrimental. Extensive efforts are being made in British Columbia to purify water to benefit all aquatic organisms. Toxicity in shellfish can be passed on to consumers, resulting in a condition termed PSP in humans, which is potentially fatal.

• IUCN Red List [Link]

  Not Evaluated

Other Comments

Although it is only distantly related to the true pearl oyster (which, in fact, is not an oyster), it can and occasionally does produce pearls. The Eastern oyster can exist in water of extreme variations in turbidity and salinity.

Contributors

Paula Osborne (author), University of Michigan-Ann Arbor.

References

Pacific Oyster Culture in British Columbia by D. B. Quayle <BR>

Production of Aquatic Animals by C. E. Nash

Abbot, R. T. 1954. American Seashells. D. Van Nostrand Co., Inc.