around. They remain in this planktonic state for around two
to three weeks; towards the end of this period, the oyster
larvae develop into “eyed larvae,” each having an umbo (the
highest part of each valve, or side, of the shell), an eyespot,
and a foot. Now is when the larvae begin searching for a
permanent “home base”—a hard substrate at the bottom of
the water column on which to attach. The ideal base would be
an adult oyster shell, but rocks, dock pilings, and sunken ships
work just as well. Upon being stimulated to settle, the larva
cements its left valve to the substrate and metamorphoses
into an adult, by discarding its velum, reabsorbing its foot,
and enlarging its gills. The adult oyster is now referred to as
a “spat.” Most spat begin adult life as a male. Once they reach
sexual maturity, which is within four months in southern
waters, some males will transform into females after the first
or second spawning. Some of those females may then return
to their original male state.
Oysters are not hunters, but filter feeders, which means
that the food they eat comes from the surrounding water.
Each oyster has an adductor muscle at the base of the shell,
which opens and closes the valves. When submerged in water,
the adductor muscle is open. Particulate matter (oyster food)
in the water is drawn in by the motion of the cilia—the small,
fringe-like whips located on the oyster’s gills. Once inside
the shell of the oyster, the cilia move in a wave-like fashion,
conducting the food particles to the mouth, and then on to
the stomach. Silt and other random intruders are rejected by
the oyster, by being collected on the mucous lining of the cilia
and then discharged from the shell. This ability to separate
food bits from silt allows the oyster to survive in waters with
high turbidity, as in most estuaries like the Kiawah River. This
filter feeding cleanses the water of various pollutants, as a
single oyster can filter up to fifty gallons of water in a twentyfour hour period.
On top of all that cool stuff, the eastern oyster is what
is known as a “keystone species.” This organism not only
provides shelter and important habitat areas for many other
ocean dwellers, but also improves the water quality of its
environment, and reduces erosion.
Sadly, the only thing that these oysters don’t typically do
is produce pearls. It does occasionally happen when home
invaders (dirt, microscopic parasites, etc.) get into the shell,
and the irritated oyster builds a