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In south Florida, sandy beaches are best developed along the Atlantic coast as far as the south tip of Key Biscayne, and along the Gulf coast. The typical Atlantic coastal beach is the result of two natural forces working together: an onshore wind-generated wave action and a longshore current moving southward. Prevailing winds, produced by southward-advancing winter cold fronts, and eddy currents, created by the northward-moving Gulf Stream, generate a current that moves past Cape Hatteras south to the tip of Florida. This current is strongest during the winter and transports large quantities of silica sand southward. Wave action mounds this sand into coastal bars. Where the bars break the water's surface, prevailing onshore winds may blow the sand up the shore where it accumulates as a coastal ridge or a series of inland dunes. Offshore bars commonly are capped by dunes to form a string of islands separated from the mainland by lagoons, locally called lakes or rivers.

The sandy coastline is constantly changing. Whole beaches may be washed away during a storm, new inlets may appear between the sea and the lagoons, old inlets may close, widen, or migrate, sand dunes may build or erode, and sandbars may form seaward of the existing beach to create a new string of barrier islands.

Sandy beaches are poorly developed south of Key Biscayne, but some occur as small pockets in the Florida Keys and the shallow bays behind the Keys. Normally the sand in the pocket beaches is composed of calcium carbonate derived from limestones along the lower mainland and the upper and lower Florida Keys. The shorelines of Florida Bay are mostly lime muds. Around Cape Sable and northward, beaches become shelly and contain increasing amounts of silica sand. From Cape Romano northward past Naples, silica sand mixed with shell forms the beaches.

The most extensive beaches on the southwest tip of Florida are the 16-km (10-mi) long beach on Cape Sable and the 10-km (6-mi) long Highlands Beach. Both are made up of shell and quartz sand over a marl base and were formed and rearranged largely by severe storms. Indeed, on Cape Sable these storms have built a coastal prairie nearly 600 m (1,800 ft) wide that extends landward in a series of low dunes. North from Naples, the sandy beach is similar to Atlantic coast beaches. However, wave action along the Gulf is weaker, the coastal dunes are smaller, and the distribution of animals and plants on these beaches differs somewhat from those of the Atlantic beaches (Martens, 1931).

Littoral sands have been compared to deserts because of the relatively low diversity of marine animals and plants living there. The shifting nature of sand makes a poor substrate for those plants and animals which attach themselves, and marine plants generally are not found on wave-combed submarine sands. Most marine invertebrates and fishes in such environments are burrowing types. Bivalve mollusks have adapted well to the soft deep sands and are represented by many species. Sea urchins, burrowing snails, crabs, and flat fish are common. However, luxuriant growths of marine algae, mollusks, barnacles, sea squirts, and worms attach themselves to rock platforms. One important biological feature of the sandy coast northward from Key Biscayne is the massive worm reefs which build upon local rocky platforms. These worms, sometimes called honeycomb worms, filter sand particles from seawater and then build sandy tubes around themselves. The reefs provide shelter for a host of fish and marine invertebrates.

Above sea level, shifting sands may form dunes or a series of dunes where plants are more common because the plant root systems act as holdfasts against the moving sand. Beach vegetation usually grows in zones that reflect each plant's adaptability to marine influences and a shifting substrate. The vegetation forms three typical zones along the Atlantic sandy coasts: a sea oats zone, a saw palmetto zone, and a scrub zone (Kurz, 1942). The sea oats zone is closest to the shoreline where the sand is least consolidated and is marked by grasses like sea oats and sand spurs or low shrubs and vines like sea purslane, the railroadvine, and the beachberry. They grow on the seaward slope and on top of the first beach dunes. The saw palmetto zone is on the landward side of the dunes and in depressions behind the dunes. This zone may form impenetrable thickets of saw palmetto, seagrape, coco plum, and wax myrtle. These two zones are usually narrow and grow close to the shoreline on the beaches in the Florida Keys, and saw palmetto is typically replaced by shrubs of baycedar and sea-lavender (Davis, 1943). On the sandy Gulf beaches north of Naples, cabbage palms appear in the saw palmetto zone forming thick stands along the beach. A third zone of variable nature occurs behind the saw palmetto zone. On the Atlantic coast, it may be a scrub zone of dwarfed oaks, sand pines, and rosemary bushes. Elsewhere the zone may be a coastal hammock, a pine flatland, or a mangrove swamp. This third zone represents a transition from the beach to the dominant type of inland vegetation. Dunes in the third zone are relatively old and stable compared to dunes of the saw palmetto and sea oats zones.