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EE
S T U A R Y C H E S A P E A K E
All About Oysters
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Oysters
Family:
Ostreidae
Species:
Crassostrea virginica
Class:
Bivalvia
Physical:
Small, fleshy gray marine
animal without bones that lives in a four-to-eight inch
shell. Its shell is rough and irregularly shaped and
is closed by one main axis.
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Range:
Found all along the United States
coast wherever tidewaters measure 10% salinity or more. In
Georgia it is found throughout coastal tidewaters.
Habitat:
Gravelly colonies between tide lines
in marsh creeks, flats, dock pilins and rock jetties.
Enemies:
Starfish, oyster drills,
oystercatchers and drum.
Feeding:
Each day, oysters pump seven gallons
of brine, decayed plants, and floating animals across special sieves
that pass along food it its mouth and stomach.
The Oyster in
Detail
The American oyster
is a small, fleshy gray marine animal without bones that lives in a
four-to-eight inch knobby white shell. Its shell is divided
into two halve called valves and these valves are held together by a
hinge. The strong adductor muscle connects the oyster to its
shell so it can come apart one-half of an inch to feed, or squeeze
shut for safety. In most oysters, the upper shell is larger
and hollowed to contain the oyster's body and the lower shell is
usually flat.
During the summer, an
oyster lays about 500 million eggs in the water to be fertilized by
the male's sperm. Soon after that a pinhead sized larva swim
around and hatch in about ten hours. In two days, shells begin
to form and two weeks later pea-sized "spat" sink to the
bottom. Living on its hollowed out shell, the oyster grows one
inch a year. Adults can live to be ten years old and reproduce
billions of times. With so many predators of the oyster, only
about one in a million will survive.
Oysters live wherever
there is firm footing to support their weight. An oyster bed
can be found in colonies between tide lines in marsh creeks, flats,
and dock pilings. Oyster beds develop in waters of about 60 to
78 degrees farhenheit. These colonies of oyster shells combine
to form one of the marshland's richest animal communities, called a
bed or rake. A tidal flow full of plankton and detritus decay
supplies food and oxygen to the oysters. Each day oysters pump
seven gallons of brine, decay, plants, and floating animals across
special sieves that pass along food to its mouth and stomach.
The pileup of dead shells makes hard banks where spat oysters settle
and grow.
The oyster has many
predators, including humans. Oyster drills are small snails
that drill holes in oyster shells and suck out the mollusk inside.
Drills take up to three weeks to eat one oyster. Starfish prey
upon an oyster by pulling apart the shells, and can eat as many as
six oysters per day. Rays crush shells with their strong jaws
while the oystercatcher bird pries them apart with its bill.
The oyster is also a
major contributor to the gem market. The pearl is produced as
an abnormal growth within the shells of some mollusks. All
oysters have an inner layer of shell made of a lustrous material
called nacre, or mother of pearl. It is composed of the
mineral aragonite and an organic substance called conchiolin.
When a bit of foreign matter enters the shell - a grain of sand, a
parasite, or an undeveloped egg - the oyster isolates it by
gradually coating it with layers of nacre. The process is slow
and it may take three years or more for a mature oyster to produce a
pearl large enough to be valuable. Pearl color varies form
white to pale shades of rose, yellow, blue, and green to the dark
gray that is the color of the black pearl. Pearl shape is
rarely perfectly round, and irregular shapes call baroque are worth
less because they are found more often. Of the thousands of
oysters gathered by pearl divers, only a small fraction have pearls.
An even smaller fraction have pearls that are gem quality.
Oysters have lived in
the seas for millions of years. Some oyster beds have been
dated as far back in time as the Cretaceous period, which was more
then 65 million years ago. The oyster is an important part of
human life, and should be around for many years to come.
The
Internal Anatomy of an Oyster
All
About Oysters Questions and Answers
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