Gray's Reef National Marine Sanctuary comprises one of the largest nearshore sandstone reefs in the southeastern United States. Named in recognition of Milton B. Gray, a biological collector and curator at the University of Georgia Marine Institute, who studied the area during the 1960s, it's located 32 kilometers (17.5 nautical miles) off Sapelo Island, Georgia. Sanctuary boundaries protect 17 square miles of open ocean. Sandstone outcroppings and ledges up to ten feet in height separate the sandy, flat-bottomed troughs in a reef that combines temperate and tropical qualities. The rocky platform, some 60 to 70 feet below the Atlantic Ocean's surface, is wreathed in a carpet of attached organisms and is known locally as a live bottom habitat. This flourishing ecosystem provides not only vertical relief, but also a solid base for the abundant invertebrates to attach to and grow upon. Grouper, black sea bass, mackerel, and angelfish and a host of other fish are attracted by the reef. Following close behind the schools of fish are the many sport fishing and diving enthusiasts who have made Gray's Reef one of the most popular recreation areas along the Georgia coast.