THE SMALLER TIDAL CREEKS:

Eugene Odum* [*in Estuarine Perspectives (1980) Academic Press] likens the tidal creeks to a circulatory system, driven by the “heart” of the tide. The analogy is excellent. Tidal creeks do provide fresh input to the saltmarsh each high tide and remove many of the by-products of growth and decay with the ebbing tide. Tidal creeks vary in growth and decay with the ebbing tide. Tidal creeks vary in size down to mere trickles, and form a dendritic pattern over most of the saltmarsh surface.

The creek banks are higher than the saltmarsh lying immediately beyond them, and these natural levees channel the water of the rising tide to the heads of the distributaries and then back in behind the levees in a sheetlike, slowly rising flood. Then, when the tops of the levees are broached, the flow occurs along the entire length of the creek.

This water flow pattern creates sediment deposition behind the levees, which in turn apparently builds up lateral pressure and outward creep which will ultimately cause slumping of the bank into the creek.

A feature of many tidal creeks is the presence of oyster bars. Oysters will settle on solid surfaces when conditions are favorable, the culmination of such growth being an oyster reef. These reefs modify the water flow in tidal creeks, producing pool and riffle structures. Oysters are responsible for much of the modification of runoff from the marsh largely by their action as filter feeders.

A low tide feature of the Sapelo creek banks is their rich golden color. The responsible agents are diatoms, microscopic unicellular algae that grow in a thin film on and in the mud surface, using the energy of sunlight to convert carbon dioxide from the air or the water into organic carbon compounds. Some of these compounds are simple sugars which attract fiddler crabs to the diatom film, and they may be seen foraging over the surface, leaving dull grey-brown mud in their wake.

One of the factors limiting the time available for feeding in the intertidal zone is the temperature tolerance of the organisms. To live on the mud surface requires a great deal of heat tolerance because of the range of temperatures encountered between low and high tides, sunny and dull conditions, and summer and winter extremes.

Having different needs and different areas of interest allows a wide variety of consumers to make optimal use of the same environment. Birds feed at low tide; herons and marsh hens feed in the shallows or on the banks and red-winged blackbirds feed on the Spartina stems looking for seeds and insects. As the tide rises mud snails become active and forage, while the marsh periwinkle and many of the insects which are to be found grazing on the Spartina retreat up the stems. Plankton and juveniles of many species enter with the incoming water and shrimp and some larger fish enter when the water depth is adequate.