Lesson #4: The Sandy Beach Community
Most of us have spent an enjoyable day playing in the wet sand and relaxing in the sunshine. Although the beach may appear devoid of life (except for a few shorebirds), there is an amazing amount of activity taking place in the sand beneath our feet. This is a habitat of constant turmoil, where there are no solid surfaces to provide shelter or attachment needed by rocky tide pool organisms. The animals of the sandy beach environment must live beneath the surface and are rarely observed.
Sandy Beach Habitats
Sandy beaches are constantly shifting, with changes resulting from wave action, the changing of tides, and the presence of an offshore longshore current. Particle size on beaches is determined by wave action. High-energy beaches receive the full impact of the wave action of the prevailing swell. On high-energy beaches, fine sands stay in suspension and are carried to deep water while course sands and larger materials remain. High-energy beaches often have steep slopes. Low-energy beaches are typically protected from the prevailing swell by a promontory or offshore rock structure, are composed of fine sand, and have gentle slopes.
Although sandy beach communities have fewer species of animals than rocky tide pool communities, those that can survive usually occur in very high numbers and dominate large areas of the beach. Most of the large animals in the sandy beach community have developed the ability to burrow into the sand for stability and protection from predators, and from drying out during low tides. Most of these beach animals are filter feeders or detritus feeders. Food for the inhabitants of the sandy beach arrives in the water as plankton, drift algae or bits of plant and animal detritus. Drift algae is usually deposited high on the wave slope toward the high tide line. This beach wrack supports a rich community of beach hoppers and insects. Beach hoppers live in burrows in the moist sand beneath the wrack.
Commonly found among beach flotsam and jetsam are shells of the Olive snail Olivella biplicata, which lives offshore the beach on sandy ocean bottom.
Another interesting organism found stranded ashore is the By-The-Wind Sailor Velella, a hydrozoan colony that drifts at sea pushed along by the wind blowing against its sail.
Predators of the Sandy Beach
The most conspicuous of the sandy beach predators is the Moon Snail (Polinices lewisii) which burrows along at low tide and subtidal depths until it bumps into a clam dinner.
The polychaete worm preys mostly on smaller inhabitants of the sandy beach. This sandworm can be up to 12 inches in length and is similar to earthworms. This burrowing creature has a row of bristled flaps running the length of its body.
Fishes are important beach predators during periods of high tide. Surfperch and sanddabs actively feed along the surf line on invertebrates exposed by wave action.
During the low tide the sandy beach becomes a banquet table for shorebirds, with each species busily feeding on its own particular specialty. Godwits, Turnstones, and the tiny Sanderlings are among the common shorebirds seen feeding along our sandy beaches.
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