Ecosystems: Coral Reefs

Flower garden coral reef
Gray's Reef is home to a tropical/temperate reef community. Though hard and soft corals live here, the corals do not form reef substrate. Rather, Gray's Reef is a sandstone formation.

Gray's Reef National Marine Sanctuary

Location: Approximately 34.2 km east of Sapelo Island, Georgia (31o24' N, 80o56' W)

Reef Structure and Physical Features: The continental shelf in this area is wide, flat, shallow, and primarily covered with sand except for occasional areas of emergent hard bottom that form reefs supporting rich invertebrate and fish communities. These reefs are less common nearshore due to weathering by river channels and deposition. However, Gray's Reef is one of the largest nearshore sandstone reefs in the southeast United States and, in terms of relief and marine life, is characteristic of live bottom reefs found offshore. It was likely formed 20,000 to 40,000 years ago during a period of dry climate when seawater in shallow areas evaporated. The resulting heavy brines percolated through sediments changing the chemical composition and forming rock.

Located in approximately 20 m of water, the reef has extensive yet patchy and discontinuous hardbottom with relief of up to 2 m. Rocky outcrops and ledges create a complex habitat that supports an array of life. There are scattered heads of stony corals and a variety of soft corals.

Coral Species: Oculina varicosa, Astrangia danae, Phyllangia americana and Cladocora arbuscula are the most common scleractinians. Leptogorgia virgulata, L. setacea, Lophogorgia hebes, Telesto fructiculosa, Titanideum frauenfeldii and Muricea pendula are the dominant octocoral fauna.

Other fauna and flora: Gray's Reef supports a combination of temperate and tropical species. There are reports of over 55 fish species, 60 invertebrate species, and 60 species of seaweeds found in the summer. A multitude of invertebrates grow on exposed rock surfaces with bryozoans, ascidians, sponges, barnacles, and hard-tubed worms forming dense encrustations. Seastars, brittlestars, crabs, lobsters, shrimp, and molluscs are other common invertebrates. The reef area is the endangered North Atlantic right whales' winter calving ground. The loggerhead, Kemp's ridley, and green sea turtles also occur in the area.

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