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Gray's Reef National Marine Sanctuary

Gray's Reef National Marine Sanctuary was named in recognition of Milton "Sam" Gray, who studied the area in the 1960's as a biological collector and curator at the University of Georgia Marine Institute on Sapelo Island, GA. The near-shore hard-bottom reef off the coast of Sapelo Island was recognized by Sam Gray in 1961 in connection with his extensive biological surveys of the ocean floor off the Georgia coast. Collections made during the surveys are under the protective supervision of the University of Georgia Natural History Museum and maintained as the “Gray’s Reef Collection.” In 1974, Jesse Hunt, a graduate student working under Jim Henry was the first scientist to study the reef. He proposed the name “Gray’s Reef” for this live-bottom habitat to commemorate Sam’s valuable contribution to the understanding of offshore habitats and marine organisms, especially those of the near-shore continental shelf of Georgia. The Georgia Department of Natural Resources submitted a nomination to the Secretary of Commerce in June 1978 recommending the designation of Gray’s Reef as a marine sanctuary.

Significant Resources

Gray's Reef is a submerged hard bottom (limestone) area that, as compared to surrounding areas, contains extensive but discontinuous rock outcropping of moderate ( 6 to 10 feet) height with sandy, flat-bottomed troughs between. The series of rock ledges and sand expanses has produced a complex habitat of caves, burrows, troughs, and overhangs that provide a solid base for the abundant sessile invertebrates to attach and grow. This rocky platform with its carpet of attached organisms is known locally as a "live bottom habitat". This topography supports an unusual assemblage of temperate and tropical marine flora and fauna. Algae and invertebrates grow on the exposed rock surfaces: dominant invertebrates include sponges, barnacles, sea fans, hard coral, sea stars, crabs, lobsters, snails, and shrimp. The reef attracts numerous species of benthic and pelagic fish, including black sea bass, snapper, grouper, and mackerel. Since Gray's Reef lies in a transition area between temperate and tropical waters, reef fish population composition changes seasonally. Loggerhead sea turtles, a threatened species, use Gray's Reef year-round for foraging and resting and the reef is part of the only known winter calving ground for the highly endangered northern right whale. Fossil bivalves and gastropods , and mastodon bones located in this area indicate that the reef was once a shallow coastal environment and an exposed land form as recently as 10,000 years BP. As a terrestrial environment there may exist at Gray's Reef extant prehistoric cultural resources.

Origin Of Gray's Reef

Gray's Reef is a consolidation of marine and terrestrial sediments (sand, shell, and mud) which was laid down as loose aggregate between 6 and 2 million years ago. Some of these sediments were probably brought down by coastal rivers draining into the Atlantic and others were brought in by currents from other areas. More of these sediments accumulated until a dramatic change began to take place on Earth during the Pleistocene Epoch, between 2 million and 8,000 years ago. It was during this time that the area which is now Gray's Reef was exposed land and the shoreline was as much as 80 miles east of its present location. As a result of this exposure, the sediments there became solidified into porous limestone sandstone rock. As the glacial ice melted, the water flowed back towards the sea, filling the basins back to their original levels.

Human Use and Values

Gray's Reef is a popular recreational fishing and sport diving destinations along the Georgia coast. Sport fishing occurs year-round but at different levels of intensity. Commercial fishing is restricted, as are military, mineral extraction, and ocean dumping activities. Little commercial shipping occurs at Gray's Reef. While the site has supported a variety of studies it currently supports reef fish and invertebrate programs. A resource characterization is in progress.

Profile of Gray's Reef Habitat's

Waters above the Reef

Planktonic (drifting) and nektonic (swimming) invertebrates are found in the waters above the reef. Planktonic species include large medusae such as the sea nettle and the cannonball jelly. Squid exemplify a nektonic species that actively pursue prey in these waters.

Flat Top Ridge

Horizontal reef tops provide habitat for sessile (attached) benthic (bottom dwelling) invertebrates which rely upon ocean currents for food, gas exchange, waste removal, and egg dispersal. Examples include hard corals, soft corals, sponges, and hydroids.


Little sediment accumulates on the vertical reef surfaces known as scarps. As a result, the bare substrate supports colonies of encrusting sponges and bryozoans (mossy animals). Barnacles, tunicates, and sea anemones are also found on these exposed surfaces.

Ledges and Crevices

Both predators and prey seek out good hiding places within the reef. Diurnal (active at day) species find refuge within the reef during the night. Nocturnal (active at night) species seek to conceal themselves within the reef during the daylight hours. Lobsters, crabs, sea urchins, and octopods prefer this type of habitat.

Slopes and Sandy Areas

Shifting sands and a lack of firm substrate preclude most sessile forms from settling along slopes and in sandy areas of the reef. Burrowing clams, mobile snails, sea stars, and burrowing polycheate worms are better adapted to life in these loose sediments.

Flat Bottom Troughs

Among the rock rubble, coarse sands, and shell fragments of the flat bottom troughs are found brittle stars, fan and tube worms, burrowing crustaceans, small crabs, and snails. This habitat is also preferred by certain burrowing echinoderms such as the sea cucumber.

Invertebrates of the reef have adapted to the specific resource characteristics of habitats described above. This ability to adapt to different, specific resources helps to decrease competition for food and space among the residents of the reef, thus allowing for a greater diversity of species within the community.

Information provided by: National Marine Sanctuaries

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