Abundance of oysters in South Carolina has remained relatively stable in recent years, although populations are lower now than they were in 1900. Declines, in part, have been related to increased siltation resulting from alterations in stream flow, overharvesting, and physical distubances to the shell bed. Diseases, particularly in areas with high salinities, have also periodically killed oysters. Intertidal oysters are also found in groups known as oyster reefs. Oyster reefs are formed by oysters growing on a firm foundation of dead shells.
Successive sets occur, joining clusters together to form a continuous group.
The intricate, three-dimensional nature of oyster reefs provides extensive habitat for numerous marine species. Mud crabs, shrimps, juvenile fishes and other organisms have been observed to seek shelter in reefs from predators as the tide rises. Loose oyster shell on creek bottoms serves as hard clam habitat as well as substrate for sponges, sea fans, and whip corals which, in turn, supply habitat for small crustaceans and fishes. Stone crabs typically reside near or in oyster reefs and feed largely upon oysters. Many larger fish forage for prey hiding among the oysters.