These are some pictures of the Eastern Oyster (Crassostrea virginica) That I took off of Bohicket Creek around Seabrook Island, South Carolina. Oysters are very well known organisms because they are commonly used as a food source. These oysters have been used as a food source in North America for as far back as humans have inhabited the east coast. There are many oyster shell rings and middens that date back to 3500+ years ago dotting our coastline from Charleston, SC to Argentina (for more info on these archaeological sites go to Historic Archaeology-Shell Rings). Despite their popularity as a food source, Oysters are very important for the diverse estuary habitats like the ones we have around the Charleston, SC area.
Oysters are bivalve mollusks that have very hard shells made of calcium carbonate. They are filter feeders, which means they filter out small organisms and detritus from the water for food. This is a natural water cleaner for these ecosystems. They keep the levels of organisms like algae, bacteria, and fungi at bay. Oysters can filter up to 50 gallons of water a day (if underwater all day). Our intertidal oysters can filter approximately 20-25 gallons a day, due to them being above water half the day. In the estuaries around Charleston, SC, with healthy oyster populations, the oysters can filter through all the water in the system approximately 5-7 times a day. So not only are they cleaning the water, when the beds are healthy, they are doing it very efficiently. They are “keystone species” meaning that if the oyster population starts to struggle, so does the whole ecosystem. They are also considered “indicator species” which means the oyster population health is considered a measure of the health of the ecosystem as a whole.
This is a major factor around areas where oysters grow. A decline in a surrounding population of oysters can mean the collapse of the entire ecosystem. We have seen this in areas like the Chesapeake Bay, which is thought to only have between 1%-5% of the oyster population they had 100 years ago. This is mainly due to over harvesting. The bay there, due to the vast pollution upriver, has a problem with algae and bacteria blooms, fish kills, water pollution, etc. because they have lost their natural filter. South Carolina’s oyster population is overall very healthy, meaning we have very little algae or bacteria blooms and less of a problem with pollution. This is due to the fact that our oysters are super efficient at taking things like phytoplankton and some pollutants out of they system before they become accumulated and cause problems.
Baby oysters are reliant on structure (usually in the form of other oyster shells) to grow on, and the old oyster shells themselves can be a big source of the calcium carbonate needed for the growth of new shells. With oysters being a large food source means that more and more oysters, with their shells, are being taken farther inland to restaurants. This takes the shells out of the natural habitat and messes up a cycle. Over time we can see the oyster population slowly dwindle due to this fact. The South Carolina Department of Natural Resources have done a great job around here working to recycle oyster shells and get as many shells as they can back out into the ecosystems to help keep this natural resource healthy.