By Tom Baird
If you like oysters, this is a great time of year. Many people say that oysters are at their most delicious in cool weather months and when harvested from cold water. We are all familiar with oysters, those tasty, ugly mollusks whose harvest supports a significant portion of the livelihood and economy of our neighbors in Franklin County. We are all familiar with the water wars between Alabama, Georgia and Florida and the effect of the diminished natural flow of the Chattahoochee- Flint–Apalachicola river system on the ecology of Apalachicola Bay. We condemn the lack of water conservation efforts of metropolitan Atlanta, the bureaucracy of the Corps of Engineers, the massive loss of water to evaporation behind multiple dams on the rivers, and sympathize with hardworking oystermen and their families for the loss of productivity of Apalachicola Bay. (Historically, Franklin County harvests more than 90 percent of Florida’s oysters and 10 percent of the nationwide supply). Yet as we enjoy a plate of chilled raw oysters, or a platter of delectable fried oysters, do we ever consider the importance of the oyster to the economy of the sea?
Oysters (Crassostrea virginica) create a mollusk reef or oyster reef. These oyster bars or “beds” become a haven for other sea life and retain nutrients on which the whole system depends. Oysters are filter feeders. Once attached to a suitable object, they consume material and planktonic organisms suspended in the water column and are nonselective. The most important foods to oysters are microscopic algae cells, bacteria and detritus - decomposing organic matter. For this reason, oysters are easily contaminated by pollutants in the water because they concentrate them as they feed.
In Florida, a marketable oyster is generally two to three years old, however, under good conditions, an Apalachicola Bay oyster can be of marketable size in less than two years. To grow best, oysters need a good water flow, proper salinity and temperature and, of course, a suitable place of attachment. Good circulation not only aids in dispersing their larvae to new locations, but assures wastes are carried away and plenty of nutrients brought to their door.
Oysters tolerate a wide range of salinities, but permanent communities do best in a range of 10 – 20 parts per thousand. (Open Gulf salinity is about 35 – 36 parts per thousand.) Since St. Joseph Bay is highly saline (there is little freshwater input), we don’t have oyster reefs in the bay. Live oysters can be found in St. Joseph Bay however, usually attached to an old wooden piling and mainly in the southeast corner of the bay where there is occasional freshwater input. Apalachicola Bay is ideal with freshwater input from Florida’s largest river. Oysters also have wide temperature tolerances, but best growth occurs between 77-79 degrees Fahrenheit.
Oysters spawn during warm months in Florida, generally from April through October and individuals may spawn several times during a season. The advent of warm water temperatures will stimulate a few oysters to spawn. This in turn triggers spawning in the rest, maximizing the number of egg and sperm in the water and the likelihood of fertilization. The fertilized egg develops into a larva that drifts in the current for two to three weeks. Settling and attachment occurs when mature larvae contact a suitable hard object, like a seawall, old boat hull, piling, or another oyster. The larvae, called spat, will readily attach to other oyster shells and soon an oyster clump grows into an oyster reef or oyster bar. Oyster bars grow perpendicular to the direction of the current. The resulting dam enables oysters to filter food from the flowing water more efficiently.
The oyster reef becomes a habitat for other sea life and as more larval oysters attach and grow, the oyster reef becomes an oasis of solid substrate in the middle of a muddy plain that would be otherwise unsuitable for other species that also require a solid base for attachment. Some examples of other organisms that inhabit an oyster bar include the stone crab (Menippe mercenaria), barnacles (Balanus spp.), the Atlantic slipper shell (Crepidula fornicata), anemones, serpulid worms, and the hooked mussel (Brachidontes reourus). Doubtless as you dined on a platter of raw oysters, you have noticed a tiny mussel or two still attached to an oyster shell. All this life on the oyster reef attracts fish that come to pick off a tasty crab or worm, and bigger fish to feed on the smaller fish. In this way, an oyster bar increases the richness and diversity of life in a bay.
The oyster reefs also alter the flushing rates and sediment transport out of the marshes and estuaries. Without the oysters to impede the flow, currents pull valuable nutrients away. In studies at the University of Georgia’s Marine Institute on Sapelo Island, it was found that more than eight tons of sediment can be dropped by an acre of oysters in just 11 days. The nutrients that the oysters concentrate are returned to the bays by the animals that seek refuge and feed on the detritus around the oyster bars.
Whether you love the unique taste of oysters in your Thanksgiving dressing or never touch the animal, there are oyster bars that are important to you. They are the oyster bars in the neighboring bays and they are an important part of the whole system that brings seafood to your table and clean water to your beaches.Although our oysters of the Atlantic and Gulf coasts do not produce pearls like the Pacific oyster, the importance of oysters to the health of the sea is more valuable than pearls are to queens.
Tom Baird has been a fisheries biologist, high school and community college teacher (oceanography and microbiology), director of a science and environmental center, teacher of science and principal in Pinellas County as well as an educational consultant. He retired from the Florida Department of Education and he and his wife divide their time between Tallahassee and Cape San Blas.