Bivalve mollusk with two asymmetric shells attached at hinge. Shell weight and shape vary greatly depending on age, location and growing conditions. Shell color usually gray-brown. Left shell, attached to substrate, is usually more deeply cupped. Muscle scar purple in color and found inside the shells where adductor muscle attaches.

Oysters are filter feeders and capture phytoplankton, dissolved organic material and other appropriately sized particles from the water column as food. Adults accumulate glycogen reserves (fatten) during the winter months and develop ripe gonads during early-late spring. Rising coastal water temperatures stimulate external spawning of eggs and sperm by adults generally in the late spring/early summer. Planktonic, swimming life stages include trochophore larvae, which develop within the first 24 hrs after fertilization, then into shelled, veliger stages (D-hinge, umbo, late umbo and pediveligers). Tides and currents carry the larvae throughout the estuary for 12-21 days until pediveligers settle and crawl to find suitable hard substrate to attach and undergo metamorphosis into sedentary stage (spatfall). Spat (<1 inch) grow to seed (>1) and adult sizes (>2) with increasing shell size. Adults form vast reef communities providing critical estuarine habitat.

Oysters are euryhaline and can survive in nearly freshwater, but salinities <10ppt inhibit gonadal development. Spatfall increases with increasing salinity, but predation and disease stymie recruitment to seed and adult sizes above 15ppt, depending on location within the estuary.