Regional Overview & Fact Sheet
The Carolinian Atlantic Region, with its numerous wetlands and tidal marshes, serves as a nursery area for many marine fishes and is an important region for shellfish. It is also highly stressed by land-based activities such as factory farming. In addition, the region combines coastal development and severe hurricanes with the most disagreeable results. The region is bounded to the south by the Atlantic coast of Florida offshore of Palm Beach, where the shelf widens and the Gulf Stream begins to diverge from the coast, and to the north by the Outer Banks and Cape Hatteras. The region is defined by a broad continental shelf, which extends up to 150 km from the coast at Georgia, and by several Coastal Plain watersheds that terminate at the coastal margin. The Carolinian Atlantic Region is bounded to the east by the edge of the Florida-Hatteras slope and the Gulf Stream.
Region defined by similar sea surface temperature, faunal composition and oceanographic currents. The northern boundary represents a major biogeographic transition.
15°–22°C (winter), 28°C average (summer)
Nearshore estuarine freshwater inflow; weak southerly longshore currents.
shelf (roughly 0–200 m): 92%
slope (roughly 200–2,500/3,000 m): 8%
abyssal plain (roughly 3,000+ m): 0%
Non-resistant rock, coastal plain sands and depositional silt-clays.
Large estuaries, coastal salt marshes, coastal embayments, barrier islands, river mouths, sandy beach, soft bottom, oyster reefs, tidal channels, and seagrass beds.
Moderately high productivity ecosystem (150-300 gCm-2yr-1).
North Atlantic right whale, fin whale, West Indian manatee, green turtle, hawksbill turtle, leatherback turtle, loggerhead turtle, diamondback terrapin, shortnose sturgeon, Atlantic sturgeon, speckled hind, barndoor skate, night shark, dusky shark, sand tiger shark, and Oculina varicosa coral.
Fishing, tourism, commercial shipping, navigation and agriculture. Pig farming in the Carolinas has created highly contaminated surface runoff and eutrophic conditions in rivers and estuaries.
Physical and Oceanographic Setting
The Carolinian Atlantic Region is characterized by a wide shallow continental platform, with a 20-meter isobath extending 25 km from shore, and a shelf break at 60 m depth occurring nearly 100 km offshore. The area is fed by fresh water discharge from several coastal plain estuaries along the North and South Carolina and Georgia coasts. The most important among these rivers include the Pee Dee River feeding Winyah Bay, and the Cooper-Santee Rivers partially supplying Charleston Harbor, both in South Carolina, and the Savannah and Altamaha Rivers in Georgia. The Florida coast is noteworthy for possessing only a single major river in this region—the St. Johns River. Moderate oceanic currents tend to flow parallel to the coast, generally northward year-round in the upper half of the region, and generally southward in the lower half. Confined to the area seaward of the shelf break, the Gulf Stream flow does not influence the current structure of this region. The Carolina shelf water generally is characterized by salinities of greater than 35 PSU. Tides can be significant, ranging from 1 to 3 m, with maximum tidal amplitudes occurring along the South Carolina and Georgia coasts. Sea surface temperatures range from 15 to 22 °C in winter and average about 28°C in summer. Geologically, almost the entire coastal region is composed of non-resistant rocks, with little relief along the coastal margin. Barrier islands occur throughout the region, but notably in North Carolina at the Outer Banks, and at Cape Canaveral in Florida. Sediments are chiefly alluvial deposits of sand and silty sand.
Owing to the flat coastal plain, gentle topography, and numerous rivers flowing from the Appalachians to the west, this region is characterized by forested and non-forested wetlands and tidal marshes. The amplified tidal range and twice-daily inundation of the flat coast also contributes to the formation of the large areal extent of tidal wetlands and flats. This physical setting strongly affects the biology of the region, with high concentrations of salt marshes, numerous nursery areas for estuarine-dependent species, and many marine fishes that utilize the coastal zone of the region. Eastern oyster reefs form at the mouths of tidal creeks flushed by the strong tidal subsidy and white, brown, and pink shrimp occur in large concentrations in the Florida-Georgia Bight from the coastline to the shelf edge. Blue crab and spiny lobsters occur in non-commercial concentrations offshore. The Atlantic sturgeon uses virtually every one of the Carolinian Atlantic Region estuaries to spawn. American shad, Atlantic menhaden, bluefish, black sea bass and bigeye scad are resident or migrant species that heavily utilize this area. The striped bass have resident river populations in each of major estuaries of the Piedmont. The offshore waters are moderately productive, with short-lived plankton blooms associated with upwelling along the Gulf Stream front.
The Gray’s Reef National Marine Sanctuary is located just off the coast of Georgia in about 18 m of water. This area contains the largest sandstone reefs in the southeastern United States, consisting of sandstone ledges up to about 3 m high, with sandy flat-bottom troughs between them. The region is extremely diverse, biologically, and attracts sportfishing and diving. Near the continental shelf break, off the Florida coast, are the world’s only known Ivory tree coral (Oculina) banks spanning this region and the adjacent Gulf Stream Region.
Human Activities and Impacts
The Carolinean Atlantic Region supports important urban areas, busy shipping ports, and important commercial and recreational fisheries resources. The coastal population has increased in the region by 160 percent between 1960 and 2000. Development along the coast has introduced a number of anthropogenic stresses to the region—including to both its nearshore and offshore ecology. Examples include elevated nutrient loads associated with urban waste and agricultural activities, pesticide inputs, and development of infrastructure on barrier island systems. In the Carolinas, particularly in North Carolina, the recent consolidation of small pig farms into large factory farms of 2,000 hogs or more has led to environmental problems in the coastal zone (Shaw 2000). The 10 million hogs in North Carolina are concentrated in the eastern part of the state near sensitive wetlands and watersheds. The high density of hogs requires the storage of hog waste in large pits that are prone to seepage and overflow into waterways, especially when heavy storms strike. High nitrogen and phosphorus content readily fertilizes the ocean waters, promoting phytoplankton growth, harmful algal blooms (HABs), reduced water clarity and shifts to undesirable species compositions. Fish lesions become common during and after storms and high flow events. There is some evidence that eutrophic conditions are promoting blooms of the toxic form of a dinoflagellate called Pfiesteria piscicida, which has been responsible for fish disease events, fish kills and sickness in humans. The destruction of wetlands on the shores has magnified these effects. Overall, the ecological condition of estuaries in the region is fair to good (EPA 2005). Forty percent of the estuarine area fully supports human and aquatic life uses, 37 percent is threatened for human and aquatic life use, and 23 percent is impaired for these uses (EPA 2005). Four out of 21 major fish stocks are overfished and seven are of unknown status (NMFS 2007).
The region is subjected to catastrophic natural events such as severe hurricanes. Housing and road development in the barrier dune systems have resulted in beach and barrier island degradation, making the region more susceptible to washout from hurricanes and habitat loss. Development in flood plains and wetland areas can disrupt sediment nourishment of marshes and lead to wetland loss. The result is conversion of coastal marshes to open water and loss of the nursery function provided by marsh habitat. Hurricanes and strong storms can rip large areas of deteriorating marsh from the land, creating coastal zones devoid of important marshes. Hurricanes also exacerbate the overflow of manure lagoons and the runoff of farm fertilizers into waterways. Hurricane Floyd struck North Carolina in September 1999 and caused massive overflows into the Neuse River. Due to the extensive presence of barrier islands along the coasts in the region, riverine outflow and the accompanying contaminants are effectively trapped in the back-island lagoons between the islands and the mainland, held close to shore, where flushing by ocean circulation is slowed.
Channelization, dredging, and dumping also take their toll on the region. Owing to the fluvial and highly sedimentary nature of the coast around navigation routes, dredging is an ongoing activity, which impacts natural communities. Dredged material is disposed in dozens of sites close to shore throughout the region. Offshore, ocean dumpsites are found throughout the region, as well as large munitions and explosives deposits on the slope off the Georgia-South Carolina coasts that have resulted from the numerous military bases and installations in the coastal zone.