Gray's Reef Live Bottom Local fishermen have been visiting Gray's Reef National Marine Sanctuary since colonial times, drawn by the consistent congregation of fish to the area. This local fishing hole, referred to historically by anglers as the "Sapelo Live bottom" is considered by some to be one of the best offshore fishing sites along the Georgia Coast. The outcroppings and ledges which make up Gray's Reef, provide the basic geologic relief on which bottom dwelling plants and animals can grow, creating what is commonly called a live bottom habitat or reef. A live bottom reef acts as a wildlife corridor, providing a maze of troughs and overhangs in which an animal can find protection from predation, food resources, and shelter against the shifting sands of the barren sea floor. Gray's Reef draws fishermen like it draws fish-congregating living organisms to one spot in the vast ocean. Live Bottom Reef Ecology Considered to be the largest near-shore, live bottom reef on the South Atlantic U.S. coast, Gray's Reef National Marine Sanctuary is located 17 nautical miles east of Sapelo Island, under 60 to 70 feet of water. The U.S. Southeast Continental Shelf, commonly referred to as the South Atlantic Bight (SAB) is a wide, gently sloping continental shelf made up of three regions: an inner shelf (0-20 meters offshore), middle shelf (20-60 meters offshore), and outer shelf (60-100 meters offshore). Past the outer shelf flows the Gulf Stream Current. As the Gulf Stream moves northward, eddies form and break off-flowing onto the SAB-bringing the warm, nutrient rich Gulf Stream water to the outer and middle continental shelf. Inner shelf areas, on the other hand, receive seasonal imput of nearshore water containing sediment, nutrients, and general river outflow. Gray's Reef is one of many live bottom reefs scattered across the SAB. The live bottom areas found on the middle and outer shelf zones are commonly inhabited by organisms intolerant to temperature changes-animals requireing warm water to maintain their body heat-reflecting the area's regular exposure to tropical Gulf Stream water. Inner shelf live bottom habitats, on the other hand, are exposed to seasonally cooler, temperate waters, resulting in a very different live bottom community structure. The live bottom of Gray's Reef NMS is located at the boundary between the inner and middle shelf zones and therefore experiences a wide variety of nearshore and offshore conditions, including changes in temperature (ranging from 14 to 28 degrees C) and salinity values. Organisms which live year-round at Gray's Reef must be tolerant species, able to adapt to the highly variable environment or they must be transitional species, able to migrate in and out of the sanctuary with changing conditions. "Gray's Reef is a transition zone for tropic and temporal species." Warm water temperatures in summer attract beautiful, tropical fish such as angels, butterfly fish, cardinals, and damsels, which migrate to the sanctuary with the aid of Gulf Stream eddies. For some species, their stay at Gray's Reef represents a reach in their extreme northern geographical range. During their time in the sanctuary they share the reef with year-round, temperate fish species including the black sea bass, gag, grouper, snapper, sheepshead, spade fish, porgy cobia, and barracuda. Geology of Live bottom reefs To understand live bottom reefs completely their geological story must be told. The reef formed when sand, shell, mud, and clay were deposited between 2-3 million years ago (pliocene age) on the sea floor. During glaciation the sea level dropped, exposing the sea floor to air which consolidated the sedimented material into limestone and sandstone. Subsequently, freshwater rivers and rain weathered the exposed limestone and sandstone, leaching minerals and metals from the hardened sediments, turning them soft and porous. When sea level began to rise with glacier melting, the porous sand and limestone was slowly eroded by centuries of waves, forming the ridges, slopes, and troughs that are present in the reef today. Through geologic time and changes in sea level, sedimentation reoccurred between 18,000 to 2 million years ago (pleistocene age) followed by recent sedimentation during the last 18,000 years (holocene age), together creating the present land formations called Barrier islands. Gray's Reef and many of the existing live bottom areas found on the South Atlantic Bight were once coastal land forms, establishing them as islands both above water historically and below water as present day isolated habitats on a sandy sea floor. top