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.