Eastern Oyster
Crassostrea virginica
(A.K.A. American oyster)

• Eastern Oysters have two shells (hence the oyster is a bivalve) which are generally grey in color. 
• The shells are often much darker in spots due to algae and other encrusting organisms. 
• The shells fit tightly together, forming a water tight seal when fully closed. 
• As it grows the shell forms many bumps, ridges and striations. 
• How each oyster will look is based greatly on where it has set and what the environmental conditions are. 

• Adults can grow to about 8”, but 4” to 5” is more typical of the Chesapeake Bay.

• The range of the oyster native to the Chesapeake Bay—the American or eastern oyster—extends well beyond the Chesapeake Bay, encompassing the east coast of North America from the Gulf of St. Lawrence in Canada to Key Biscayne, Florida, and south through the Caribbean to the Yucatan Peninsula of Mexico and to Venezuela.

• Oysters are found on the bottom throughout the Chesapeake Bay.

• Oysters feed on the algae in the Chesapeake Bay.
• As they eat they act like a filter on a fish tank.
• Oysters filter out algae and tiny particles that cloud the water.

• Oysters reproduce by spawning into the water column. This generally takes place between June and September. Male and female oysters cast their gametes into the water, where fertilization occurs by chance.
• Six to eight hours after fertilization the new larvae has formed the first part of its shell. Cilia have also developed which allow it to swim.
• The larvae swim for two to three weeks before heading to the bottom to find a place to set.
• At this stage the oyster has a foot which is uses to find a suitable place to set.
• When it goes to set, a gland in its foot secretes a drop of liquid cement, which attaches the oyster to the bottom. At this point it is now called Spat.
• Oysters prefer to set on the shells of other oysters but other hard, clean substrates are also used.
• Oysters will grow to about three inches in three years, unless the water is of low salinity. Then it may take 4 to 5 years to reach three inches.
• Oysters under a year old are about 90% male. As they grow many will change sex, and older oysters are about 80% female.
• Oysters prefer salty water with an optimum salinity range of 10ppt (parts per thousand) to 28 ppt.
• Extended periods under 5ppt salinity can cause significant mortality.

Oystering Tips:

• Commercial Regulations: http://www.dnr.state.md.us/fisheries/regulations/commregs.html
• Recreational Regulations: http://www.dnr.state.md.us/fisheries/regulations/recregchrt.html
 

Fun Facts:

• Oysters have been around for 15 million years and in some places their shell deposits are 50 feet thick.
• Many people like to eat oysters. For that reason, they are a very important seafood resource for the Chesapeake Bay.
• Oyster beds or reefs form a suitable habitat for other living creatures.
• Oysters at one time were very plentiful. However, over the years oyster diseases, MSX and Dermo have killed many of them.
• In the mid to late 1800’s conflicts between oystermen who used different gear types and between those in Maryland and Virginia, escalated to deadly levels in a time known as the Oyster Wars.
• In 1868, Maryland formed the Oyster Navy to police the waters of the State to try and enforce oystering regulations and help deter the violence.
• The city of Crisfield is built on a foundation of oyster shells.

In Focus: Oyster Restoration in the Chesapeake Bay

For more information on eastern oysters and their management, please contact Chris Judy or Eric Campbell.