Sandy beaches are dynamic environments that are constantly changing in size, width and profile as the unconsolidated sand is reshaped by the action of waves, tides and currents. In the winter and spring, large waves can move most of the sand off the beach face and into the surf zone where it forms sand bars. When the waves are smaller, sand is moved gradually back on to the beach face. California beaches are often widest in the late summer and fall and narrowest in the winter and spring months.
Coastal watersheds are the major source of sand for California beaches. Sand from watersheds flows down creeks and rivers and is deposited at the mouths, forming sandy beaches. Longshore currents generated by waves pick up sand from these larger deposits near creek and river mouths and move it along the coast to form more beaches. The SBC coastline experiences strong west to east longshore transport of sediments associated with the prevailing NW wind and swell pattern. ENSO events and episodic storms strongly influence sediment supply, erosion and condition of SBC beaches.
Sandy beaches are characterized by a lack of attached plants in the active intertidal zone and to a casual observer may appear to have few inhabitants. However, the constantly moving sand of the beach is a very rich and productive intertidal habitat that supports a diversity of wildlife, particularly in California. The low in situ primary production characteristic of beaches means beach food webs depend almost entirely on organic material imported from other sources. The ocean provides the majority of these subsidies to beaches. In the Santa Barbara Channel, two major sources of organic material for beach food webs are phytoplankton and drift algae. The biomass of the beach macroinvertebrate community is often largely composed of suspension-feeding species who feed on phytoplankton, such as sand or mole crabs, Emerita analoga and clams (Donax gouldii, Tivela stultorum). However, an average of 40% of the intertidal species of beaches consume drift algae or wrack, generally preferring giant kelp. This diverse group of consumers includes talitrid amphipods, oniscoid isopods, beetles and flies.