Oysters reproduce by releasing sperm and eggs into the water. Within six hours, fertilized eggs develop into larvae, which become fully shelled within 12 to 24 hours and are ready to attach themselves to a solid substrate within three weeks.
Some species of oysters have separate sexes, but their reproductive organs contain both sperm and eggs. They are able to change sex from year to year. Some oysters are hermaphrodites and theoretically can fertilize their own eggs. When food is abundant, females are prevalent, but when food is scarce, there are more males. Spawning is temperature-dependent, and occurs at 68 degrees Fahrenheit. Females release millions of eggs at a time.
When an oyster larva is ready to settle, it grows a foot and finds a place to establish itself. Usually this is an adult oyster shell that is part of an oyster bed, but it might also be broken oyster or clam shells. The young oyster, known as a spat, cements itself to the new surface and slowly metamorphoses into an adult oyster. Oyster beds sometimes form reefs that create complex ecologies, stabilizing bottom sediment, creating breakwaters for shorelines, filtering and cleaning water and creating habitats for a great variety of marine wildlife, including barnacles, sea anemones, worms, crabs and an abundance of fish.