1.The Eastern Oyster
The eastern oyster，Crassostrea virginica, ranges naturally from the Gulf of Saint Lawrence in Canada to the Gulf of Mexico, the Caribbean, and the coasts of Brazil and Argentina. The eastern oyster is one of the few oyster species that can construct extensive reefs that, like corals, are primarily dead shell with a veneer of live animals.
Oysters are also unique because they are a harvestable resource and provide critical habitat. Many commercially important oyster reefs are sustained through cultch plantings and stocking seed oysters onto reefs. Early efforts at cultivation involved little more than transplanting small oyster from one area to another where they could grow faster and survive better. During the 1950s,hatchery techniques were adequately refined for commercially farmed oyster.
2.ECOLOGY
The eastern oyster may be found on subtidal or intertidal reefs and provides important ecological functions in estuaries throughout its geographic range. These functions are related to both the reef structure formed by oysters and the reefs support over 300 species of marine organisms that are part of the food web leading to economically important species. Oysters are capable of filtering four gallons of water per hour densities and improving water quality. As a result, oyster reefs are critical to maintaining species diversity and the natural production of estuaries where oyster reefs have had a dominant historical presence.
3.Life Cycle
Trochopheore 5-12 hours after fertilization, a motile trochophore develops from the egg.
Fertilized egg Eggs are fertilized by sperm in the water.
Unfertilized egg Each adult female oyster may produce anywhere from 25-150 million eggs, depending on the size of the oyster.
Adult Oysters Male and female oysters release eggs and sperm into the water.
Spat Settting occurs when the larva cements itself to a hard substrate and metamorphoses into a tiny oysters called a spat. Spat may refer to any small oyster. At that point it can never reattach or move again.
Pediveliger 12-20 days post-fertilization, the oyster larva develops “eye-spots ” and a “foot”, and is referren to as a pediveliger. The pediveliger settles to the bottom and seeks out suitable substrate for setting.
Veliger Within 12-24 hours, a veliger develops with the characteristic strait hinged, D-shape of bivalves. At this stage, the veliger larvae are capable of feeding on microscopic algae.
4.COMMERCIAL IMPORTANCE
With the decline of historically important areas such as Chesapeake Bay, the Gulf of Mexico supplies about 72% of the national production. The state of Louisiana is the biggest producer of oysters. Gulf oysters are harvested manually (by hand and with tongs, also known as rakes ) and mechanically ( with towed scrape dredges) from public waters or private leases in areas that are approved for harvesting by state health authorities. Harvested oysters are quickly transported to processors where they are cleaned, stored ,chilled and processed. Shell recycling for cultch is an important by-product from the processing industry.
Oysters are delicious, as well as nutritious. About 20 million Americans annually enjoy eating raw oysters with few problems. However, some individuals are susceptible to bacteria which occur naturally in seawater and in raw oysters. These bacteria are harmless to healthy consumers but can prove deadly to those persons with certain medical conditions. These conditions include liver disease, hemochromatosis, diabetes, stomach problems, cancer, immune disorders, including reduced immune response from cancer treatments, and long-term steroid use. If you are, or think you may be, in any of these risk categories you should not eat raw oysters. However, fully cooked oysters can be safely consumed.
Photos courtesy of Loren Coen, South Carolina Department of Marine Resources; Edward Hernaon, Design Lab Marketing; Bradley Randall and Scott Gordon,Mississippi Department of Marine Resources; Scott Rikard, Auburn University Shellfish Laboratory; LoDon Swann, Mississippi-Aalbama Sea Grant Consorium; and Tom Ulrich.
Produced by: Sea Grant Mississippi-Alabama
Supported by: marin resources division conservation and natural resources
Mobile Bay National Estuary Program
Department ot marine resources Mississippi
Tonger boat Dredge boat
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