A sandy beach appears to have little life particularly along the water’s edge where wave action is continuous. Strong waves remove the finer sediments quickly resulting in coarser material and more rapid drainage. In quiet, protected areas the waves have less energy and the fine sand remains. These conditions are more likely to support animal life, particularly burrowing organisms such as polychaete worms and some clams. Crustaceans such as mole crabs (Emerita talpoida) burrow in this environment and filter feed small food particles with their antennae.
The size and composition of beach materials varies with the seasons as well. Sometimes a winter berm will form at the upper portion of the beach. Waves may also remove sand and form a sand bar slightly offshore. In all cases the sandy beach is a dynamic system in which sediments are constantly being moved and relocated. The structure of the sediments may also vary vertically along the shoreline with fine sand particles closer to the water’s edge and more gravel type material at the upper section where the wave energy is most intense. The wind can also contribute to the movement of sand and result in the buildup of dunes. These systems of moving sand along beaches and the formation of dunes are called barrier beaches and are very important in protecting upland areas from erosion and coastal storm damage.
Other physical factors along a sandy shoreline include a relatively uniform temperature and salinity profile particularly in areas of fine sand particles. However, oxygen concentrations may vary depending on particle size. The larger the particle of sand, the greater the exchange rate between the water and the atmosphere.
Sandy beaches often have a wrack line in which various species of seaweed as well as eel grass wash up on the beach and may harbor small animals such as mollusks, sandhoppers, bryozoans, and tube worms. Occasionally a horseshoe crab may swim in the shallow water, and many species of shorebirds will be seen parading up and down the beach edge feeding on mole crabs and other small critters.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.