The extensive barrier island system along the east coast of Florida is the largest in the United States, consisting of approximately 189,300 hectares (467,700 acres) (Kaplan 1988). In east central Florida, barrier islands separate the Atlantic Ocean from the Indian River Lagoon (IRL) and are an important defense against hurricanes and major storms, buffering mainland Florida against large waves, heavy winds, and storm surges. Barrier islands are dynamic features of the landscape that form in two ways: 1) from longshore drift currents move sands southward along the coast; and 2) from the emergence of underwater shoals (Otvos 1981). It is believed that Florida’s barrier islands originated during the Pleistocene epoch (1.75 million to 11,000 years ago) when rises in ancient beach and their associated sediments lithified into coquina (rock). Traces of this coquina system, called the Anastasia Formation, can be found from St. Augustine to Boca Raton, Florida (Tanner 1960b).

Whether barrier islands begin as simple sandbars, or as emerged shoals, they gradually accumulate sand due to wave action and winds. It is this build up of sand along the coast that forms the well developed beaches, dunes and maritime forests along Florida’s coast. Wave action is constantly at work eroding sand from some areas of the barrier island system, while simultaneously depositing this eroded sand into different areas via longshore drift, storms and hurricanes. Accretion of eroded sediments generally occurs either parallel to the coast, or at the ends of barrier island systems, rather than seaward. In general, sands tend to be carried southward along the coast, and are deposited as they encounter the northern ends of barrier islands or other structures such as jetties. Data from Pilkey et al. (1984) suggests the Florida coastline has been eroding landward at a rate of 0.3 – 0.6 mm per year.

The substantial system of barrier islands in the area of the Indian River Lagoon encompasses a variety of habitat types. In the immediate vicinity of the shoreline are beaches, dunes, and swales. Beyond the beach zone are coastal strand, also called scrub, maritime hammocks, spoil islands, and the mangrove fringes that border the Indian River Lagoon.

Select a barrier island habitat to explore:

                                            Barrier Island Habitats
                                                      Beaches
                                                      Dunes
                                                      Scrub
                                                      Maritime hammocks
                                                      Mangrove fringes  

Report by:  K. Hill, Smithsonian Marine Station
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Page last updated: Dec. 17,  2001