Barrier islands

Sea level is 300 feet higher today than it was 15,000 years ago. When rising global temperatures began to melt glaciers, the sea started to rise. Massive flooding occurred, separating sand dunes and beaches from the mainland.

Today, a complex system of elongated islands surrounds most of Florida. The detached strips, called barrier islands, help shelter the mainland from the effects of wind and waves.

Acting as the first line of defense, barrier islands are low-lying and highly vulnerable to the forces of wind, waves and storms. In a constant state of flux, these islands move constantly due to sand deposited by storms and wave action.

Varying in size, barrier islands may contain a range of ecosystems — sandy beaches, dune systems, maritime forests, interior wetlands, salt marsh and mangroves.

Narrow channels, or inlets, separate barrier islands from one another. Inlets allow water to flow in and out of the semi-enclosed bodies of water, known as estuaries, that lie between barrier islands and the mainland.

A number of ecosystems may exist on a barrier island.

Estuaries and wetlands

Estuaries are formed through the mixing of upland freshwater and saltwater from the ocean. Florida’s estuaries vary in size, type and amount of salinity, but all are an essential part of Florida’s ecological productivity, serving as spawning, nursery and feeding areas for a wide variety of marine life.

Wetlands are low-lying areas that serve as transitions between land and water. Florida has both freshwater and coastal wetlands, ranging from small, isolated patches of upland marsh, to vast, complex systems like the Everglades. In addition to supporting an incredible variety of plant and animal life, wetlands also maintain water quality and are essential to flood control.

Coastal marshes are wetlands that border estuaries. These open tracts of shallow water nurture many types of grassy plants and, like estuaries, are breeding and nursery areas for a multitude of fish and shellfish.

Marshes, such as this area of the Everglades, are an essential part of Florida's ecology.

These marshes are also important habitat for a wide variety of wildlife and, because their grasses trap and filter pollutants, they provide natural waste-water and pollution treatment. They also reduce shoreline erosion, help control flood waters and replenish groundwater supplies.

Mangrove forests of tropical mangrove trees hug much of Florida’s southern coasts. Like the estuaries they border, and the salt marshes of other areas, the dense mangrove forests help prevent shoreline erosion. An important line of defense from storms, they also supply food and shelter for many animals, birds and fish.

Dune systems

Beaches and dunes are the shoreline’s first line of defense from wind, waves and storms.

Plants are essential to the health of beaches and dunes - their deep roots help stabilize the dunes.

Gentle summer waves shift sand from offshore onto the beach, where much of it blows further inland, becoming trapped in vegetation and forming dunes. Hurricanes or other strong coastal storms reverse this process, carrying sand from dunes back into the sea.

Whether eroding, building up or shifting with the natural forces of wind and water, these dynaminc areas change constantly, their shapes and slopes dependent on different flows of sand.

The plants that grow in these areas must be very hardy to live in the extreme conditions of salt spray, flooding, wind, heat and dryness. Furthermore, they are essential to the health of beaches and dunes because their deep roots help stabilize the dunes by holding the sand together.

Maritime forests

Landward of the dune systems can be found shrub zones and maritime forests, both host to well-developed plant and animal communities. The maritime forests not only provide important habitat, but also help stabilize near shore areas and provide protection from storms.

Mangrove forests help prevent shoreline erosion.

Coral reefs

The skeletal remains of millions of tiny animals, called coral polyps, form coral reefs. Coral colonies exist in a number of shapes and sizes, and create habitats for a host of marine life. As they require clear water, bright light and warm temperatures to survive, the coral reefs of the Florida Keys are the only living reefs in the continental United States.