Animal Life on the Beach

Although the beach itself appears nearly devoid of life, there are many species that live there or are dependent on its availability for feeding or nesting. At lower levels of the beach, where the surface sand remains damp throughout low tide, there are often large patches of diatoms which give the surface a golden sheen, similar to diatoms found on exposed mud banks in the intertidal areas of the tidal creeks, and during summer and fall the lower beach is often covered by a layer of green which is a flagellated euglenoid alga which migrates up and down in the sand in much the same fashion as the marsh diatoms.

At low tide it is common to see many small holes in the sand surrounded by a ring of small, brown, cylindrical pellets. The hole is the burrow of the ghost shrimp, Callianassa major, and the pellets are fecal matter which has been deposited on the surface by the animal in the burrow. The fecal pellets contain bacteria and undigested algal cells and cell fragments, along with clay particles, and could provide a neatly packaged source of organic carbon for deposit feeding animals. Blue crabs (Callinectes sapidus) and pagurid crabs (Pagurus spp.) can readily ingest C. major fecal pellets, suggesting that the fecal pellets may be an important food resource for subtidal species.

One permanent resident of the beach is the ghost crab, Ocypode quadratus. In addition to nocturnal predatory foraging, O. quadratus engages in deposit feeding during daylight hours, using its minor chelae to transport substrate to the buccal cavity and then to remove feeding pellets, aggregations of uningested substratum. Their behavior is similar to that of the sand fiddler crab, Uca pugilator, which can also be found on some sheltered areas of beach and in sandy substrate high marsh habitats. Both O. quadratus and U. pugilator are highly efficient at removing algae from sand particles. Deposit feeding by ghost crabs is restricted to areas with visibly dense patches of diatoms.

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