Indian River Lagoon
Species Inventory

Barrier Islands

The extensive Indian River Lagoon 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). These islands separate the IRL from the Atlantic Ocean, and are an important defense against hurricanes, large waves, heavy winds and storm surges.

Photo credit: R. Richards

Barrier islands form in two ways: from longshore drift currents that move sands southward along the coast; and from the emergence of underwater shoals. Florida's barrier islands are believed to have originated during the Pleistocene epoch (1.75 million to 11,000 years ago) when uprisings of ancient beaches and their associated sediments were compressed into coquina (rock). Traces of this coquina system, called the Anastasia Formation, can be found from St. Augustine in the north to Boca Raton in the south.

Barrier islands’ shorelines are constantly shifting in response to wind, waves, tidal action and sediment shifts. In a natural state, the shoreline of a barrier island migrates oceanward or retreats landward as the forces of erosion and accretion (deposition of sediments) occur.

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; simultaneously, waves deposit this eroded sand into different areas via longshore drift, storms and hurricanes.

Deposits of eroded sediments generally occur 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.

An aerial view of the Indian River Lagoon. Credit: J. Thurlow-Lippisch

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.

Human Impacts

Florida's barrier islands have been extensively developed and support a large human population, leaving little of the original landscape unaltered.

Credit: T. Dunkerton

Florida's beaches are rated among the finest in the U.S. and draw tourists from all over the globe to swim, surf, bask in the sun, snorkel, fish and sail. As a result, tourism has become the premier industry in Florida, supporting more than 1.6 million jobs. In 2019, approximately 131.4 million out-of-state visitors came to Florida, spending $98.8 billion dollars.

While development and tourism have been an economic boon to Florida, they have also brought and compounded associated problems that must be continually addressed.