Nannygoat Beach is the most readily accessible
beach on Sapelo and provides and assortment of geological features.
The sand itself has a history.
Differing in composition from the Pleistocene sands of the central
part of the island, this fine grained, well sorted quartz sand has
originated most recently from the landward transport of sand from the
shallow continental shelf, primarily transported shorewards by wave energy.
Mud on the beach comes from several sources.
Soft, oozing fecal mud is found in the troughs of the runnels. This
is derived from the activities of ghost shrimps and tube worms inhabiting
the lower beach. Larger mud balls (looking deceptively like
small stones) may be found occasionally. These result from the
breakup of older Holocene marsh terraces which periodically become exposed
on the beaches.
The beach is an area characterized by
sand, tides, wind and waves. As it can vary from season to season,
day to day, and in a storm or calm weather, so those organisms, which
live here, have to grow opportunistically.
The low water mark has its characteristic
fauna. This is the area in which to find hermit crabs scurrying about
in their borrowed shell and sea pansies lying like purple valentine
hearts on the sand surface. In the retreating waves small amphipods
– looking and moving like overgrown fleas – are eagerly sought by sandpipers
and other shorebirds.
The lower beach provides only indirect
clues to many of its other inhabitants. These spend their lives
buried below the surface and their burrow entrances or linings are
seen much more commonly than are the architects of the burrows.
The ghost shrimp (Callianassa) produces a characteristic array of fecal
pellets on the sand surface, and when the wave swash has removed the
top few centimeters of sand, the thick mud tube entrance to its burrow
may be found readily. Onuphis, a tube worm, produces thin parchment-like
tubes, composed of chitin covered with fine sand, while another worm
Diopatra cements pieces of shell and Spartina debris into its distinctive
Further up the beach, the community is
constrained by the shifting nature of the substrate, by the physical
effect of currents and wave motion at high water, and by desiccation
at low water. Residents tend to burrow into the sand; deposit
feeders are found more often in low energy, silty areas while filter
feeders appear to prefer sandy high energy areas. This then is
an area where the activity appears clandestine. At low tide ghost
crabs furtively search the beach debris for an easy meal, and beach
hoppers and smaller crabs burrow under stranded horseshoe crabs and
Spartina wrack deposited at the high tide line.
In the shallow water in ripple marks
and runnels, colored patches may be seen. The colors are brought
about by the presence of micro-algae (microscopic one-celled simple
plants), euglenoids producing green patches and diatoms producing golden
patches. The beach in warmer weather and low light conditions (early
morning, late afternoon and overcast weather) shows intense patches
of color, especially between low and mid-tide levels. Euglenoids
are motile and may be found at greater depths below the sand surface
as the intensity of the light increases throughout the day.
One member of the animal kingdom which
is often found stranded on the beach among the debris on the high
tide line is the plant-like, often brightly colored gorgonian coral.
Gorgonians require a solid base on which to grow. A profuse mass
of gorgonians can be seen on debris at the bottom of Cabretta Creek at
very low tides and it is assumed that this may well be the origin of
the majority of the material found on the beach.
Beyond Nannygoat is another Holocene
barrier beach know as Cabretta. At its northern end there is
an eroded relict Holocene saltmarsh (X) exposed in a series of terraces,
representing at least three subenvironments. Oyster clumps reflect
earlier tidal creek banks. The presence of mussels indicates short
Spartina high marsh. The sandy sediments and Salicornia and Juncus
stems represent a different, even higher marsh. This area also
provides mute testimony to the massive erosion of more recent beach
sands from this northerly aspect.
Another feature of north Cabretta is
the presence of washover fans. These are points where beach
sand has been driven landward to overlie the modern marsh and are formed
by the erosion of the dunes.
Central Cabretta currently has a slough
behind the beach foredunes which has varied greatly in character; it
has been both open to high tide influence and cut off by a bar to become
self-contained. Such a feature may last weeks or years depending on
circumstances. This slough has already developed a limited saltmarsh
environment of its own.
The ‘big hole’ (Z) area comprises the
northern end of Nannygoat Beach and the southern end of Cabretta, which
are separated by Cabretta Creek. This is an area of erosion, as
can be seen by the large number of uprooted trees and the exposure of
old saltmarsh muds as a result of a significant retreat of the shoreline.