Chemosynthetic communities are not found on the continental shelf although they do appear in the fossil record in water shallower than 200 m (656 ft). One theory explaining this is that predation pressure has varied substantially over the time period involved (Callender and Powell 1999). More than 50 communities are now known to exist in 43 Outer Continental Shelf (OCS) blocks. Although a systematic survey has not been done to identify all chemosynthetic communities in the Gulf of Mexico, there is evidence indicating that many more such communities may exist. The