THE CONTINENTAL SHELF/NEARSHORE:

The continental shelf off the coastline is shallow and about 70-75 miles wide. The inner boundary of the Gulf Stream coincides approximately with the outer edge of the shelf. This major oceanic current flows northeast, contrasting with the coastal water flow, which is generally to the south. Because of the wide shelf and the containing influence of the Gulf Stream, the shelf water is discretely different from that of the open ocean. It is influenced by input from the Savannah and the Altamaha rivers, together with that of several minor rivers, which discharge into the coastal water via the saltmarsh distributary systems. The water is mixed via the combined agencies of tides, wind and waves.

The inshore water near Sapelo Island is therefore less salt than true seawater and turbid because of the suspension of clays, phytoplankton (microscopic plant life), and fine particles of organic matter. This turbidity prevents the light penetration necessary for photosynthesis. Consequently, there are few plants growing on the nearshore bottom. However, it appears that the phytoplankton suspended in the water has adapted to low light levels and that the turbulence created by wave action exposes these organisms to some light at sufficiently frequent intervals for them to be very productive. Much of the activity here is unseen. Within the bottom sand, bacteria grow on an accumulation of organic matter. They, in turn, become part of the food supply of larger organisms and also produce nutrients which may be used by phytoplankton.

Just offshore there is a system of shoals, which can be seen as a line of breakers, or occasionally exposed as sandbars at low tide. These shoals influence the pattern of sedimentation, which is also affected by wave action and longshore currents. On Nannygoat Beach (E) the shoals are themselves strongly influenced and determined by the ebb flow delta pattern of Doboy Sound. Cabretta’s wave-formed spits and shoals are commonly exposed at low tide. This is a very interesting area in which to see evidence of a large range of intertidal and displaced subtidal animals.

The animal community in the nearshore must contend with poor visibility and make use of other sensory capacities. The dominant animals found here are shrimp; horseshoe crabs (a living fossil, not a crab at all); a variety of worms, both free-living and tube worms; molluscs, especially bivalves and whelks; sea pansies, at the low water mark; and an assortment of fish which tends to vary from season to season. Mullet and channel bass are found in summer, and sharks and dolphins feed fairly close inshore.