Photosynthesis is conducted by a microflora of bacteria, cyanobacteria, diatoms, and autotrophic flagellates living in the interstices between sand grains or attached to the surface of the grains. Macroalgae are rare but will occur if hard surfaces such as shells or buried stones are available. The microorganisms and small macroalgae may also grow as epiphytes on the stems of salt marsh grasses, the leaves of seagrasses, or the aerial roots of mangroves.
Many of the animals of the beach are tiny and serves as links in detritus food chains, feeding on decomposers such as bacteria and fungi or themselves consuming organic detritus. Among the many permanent residents in the infauna are rotifers, some copepods, ostracods, flatworms (turbellarians), and nematodes.
The macrofauna of exposed beaches consists of polychaetes (bristleworms), crustaceans (isopods, amphipods, crabs, and ghost shrimp), and mollusks. They include both filter-feeders and deposit-feeders. Burrowing is a common strategy to avoid dessication and predators during low tide.
Scavengers and predators are abundant, searching for prey just below the surface at low tide or for sealife that has been stranded on the shore. Fish visit the beach during high water. Shorebirds, however, are the most visible predators, probing the sand at low tide or chasing scurrying prey as waves roll onto the beach. Sandpipers, plovers, and oystercatchers are common. Most shorebirds breed in the Arctic and migrate along well-defined flyways to wintering grounds in both the Northern and Southern hemispheres. Estuaries, beaches, and salt marshes are important stopover places along the way.
Invertebrates of the sandy shore:
Shorebirds of sandy shores: