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
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
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.