CUMBERLAND ISLAND An Ecological Survey of the Coastal Region of Georgia NPS Scientific Monograph No. 3

The Georgia mainland is bounded on the east by a functional system of barrier islands, marshes, and coastal waters. The system is influenced by the movement of materials into and through it, especially from the mainland rivers and from coastal areas to the north via the southward-flowing littoral currents. The region is further influenced by animals migrating into and through it from other areas.

The chain of barrier islands extends the length of the Georgia coast. The islands were formed during the last 10,000 years probably as a result of dune ridges; they formed at low stands of the sea and were inundated when sea levels rose again. Barrier beaches form on the islands from littoral sands. Wind-blown sand from the beaches is trapped by vegetation to form dune ridges which ultimately become stabilized by salt-tolerant vegetation. The dunes protect the island from sea winds, salt spray, and storm tides and allow the establishment of forest vegetation. The major habitats of the island interior are live oak forests, pine forests, fields, and sloughs.

The islands absorb much of the energy from tides and waves and allow sediments from the continental shelf and mainland rivers to be deposited in the sheltered lagoons behind the islands. The lagoons become filled with sediments to form marshes. Deposition on the marsh continues as the waters spill onto the marsh at high tide, but increases in marsh elevation due to deposition are just about offset by rising sea levels. Few plant species can withstand the stress imposed by high salinity and daily inundation by tidal waters, and marsh vegetation is monotonously uniform. The tidal marsh is predominantly smooth cordgrass, although there is a zonation of species related to gradients in salinity and elevation.

The marshes are very productive and export nutrients to the estuaries and waters of the continental shelf. Smooth cordgrass accounts for most primary production in the marsh. Mud algae and phytoplankton, though less important than cordgrass, also contribute substantially to primary production. A relatively small proportion of the total energy flow is through the grazer food chain. Most energy and nutrients pass from the marshes into the estuaries in the form of detritus particles which form the base of an aquatic detritus food chain that supports economically important estuarine organisms. Nutrients exported by the marshes are trapped in the estuaries, which are more fertile than either the rivers that drain into them or the adjacent offshore waters.

All of the major elements of the island-marsh-estuary system are intimately interrelated. Sand beaches and dunes protect the islands from erosion and inundation by the sea. The islands protect the marshes from the force of the sea, and the marshes trap sediments discharged from mainland rivers, protecting the aesthetic and recreational qualities of the island beaches. The marshes contribute much of the primary production for aquatic food webs which support the fisheries resources of the open waters. The open waters remove waste materials from the marshes, circulate nutrients, and transport certain types of organisms.

Certain elements in this functional web are particularly sensitive to the disrupting influences of human activities. Seemingly insignificant actions affecting some sensitive areas ultimately may have far-reaching effects on other elements of the system. Man has exerted his influence on the region for centuries and, especially in recent years with increasing industrialization on the mainland and recreational development on the islands, often has placed severe stresses on the natural system.

The ecological characteristics of the coastal region make it peculiarly sensitive to pollution. The processes that concentrate nutrients in the estuaries to form a "nutrient trap" also concentrate pollutants such as heavy metals and chlorinated hydrocarbon pesticides. Many estuarine organisms harvested by man (especially oysters, clams, and other mollusks) concentrate pollutants (e.g., radionuclides, chlorinated hydrocarbons) in their tissues at levels potentially dangerous to the health of the consumer. Arthropods such as shrimp and crabs are sensitive to even small quantities of chlorinated hydrocarbons. The concentration of many of these pollutants already has reached disturbing levels. Concentrations of heavy metals are high in some organisms on the Georgia coast and some areas have been closed to harvesting because of this.

Because of low oxygen content, estuarine waters are also quite sensitive to oxygen-demanding pollutants such as domestic sewage. Sewage also contaminates clam and oyster beds causing them to be unusable as a food source.

For planning purposes, the coastal zone logically may be classified into four basic management units: the mainland, the islands, the marshes, and the coastal waters. These in turn may be classified into management subunits: the specific habitat types (e.g., beach-dune complex, live oak forest, low tidal marsh, etc.).

Future residential and industrial development should be restricted to the mainland. Pollution standards should be strictly enforced and a continuous monitoring program should be established. Industries that would place great demands on an already overtaxed ground water supply probably should not be encouraged to locate on the coast. Existing industries should be required to make greater use of surface water and develop and implement technology for recycling.

The insularity of the islands should be preserved; there should be no additional bridges or causeways to the islands. The islands should be maintained as nearly natural as possible. Vulnerable components of the island ecosystem that should receive special protection include dune vegetation, sea turtle rookeries, sloughs, wading bird rookeries, mature live oak forests, and endangered and unique wildlife (e.g., pocket gophers, bald eagles, alligators).

Marshes and estuaries generally should be preserved in a relatively natural state for public use and enjoyment. Marsh alteration for aquaculture and waterfowl, while desirable and acceptable forms of marsh management, should be regulated.