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Tales of the Coast
Sharing the Coast

Barrier Island Ecosystems

Barrier islands are relatively small and very dynamic landforms, yet a number of unique ecosystems can be found successively from the ocean side to the bay side of the feature. Each barrier ecosystem changes over time with the effects of storms and coastal processes.

Barrier islands include sandy beaches, forests, and marshes on the bay side. Dunes and various types of vegetation are affected by salt water, whether in waves or overwash sediment. Despite the volatility of this coastal environment, plants and animals, including rare and endangered species, make their home on barrier islands.

The nearshore is the underwater area just seaward of the beach. In this zone there are sand bars and a limited amount of marine life. Because it's a high-energy environment with waves breaking constantly, the nearshore isn't home to an extensive amount of plants or animals. The nearshore is also the zone where waves break before running up onto the beach.
The beach of a barrier is a sand-dominated environment consisting of the foreshore that is lapped by waves and the typically dry backshore. The beach protects landward environments and developments from waves and flooding. Storms and seasonal wave activity change the shape of the beach, resulting in eroded scarps along the beach where sand was scoured away and areas of accumulation where the sediment was returned by low-energy waves.

Landward of the beach is the dune area, where a large ridge or ridges of sand are piled up. They are initially formed by aeolian transport, or movement of sand by the wind.

Once the dunes begin to grow from the accumulation of wind-transported sand, vegetation helps to stabilize and increase these landforms. Salt-tolerant grasses are crucial for the development and growth of dunes because they catch sand grains, hold them together with their roots, and then grow taller to catch more sand. These grasses can withstand salt water spray and piling sand.

When overwash comes through the dune line, it deposits thin layers of sediment across the barrier, which are known as washover fans. These are very unique and important environments for wildlife because they're moist but barren of plants. Many birds and shellfish will nest or forage for food there.

After a period without inundation, washover fans become vegetated and are known as barrier flats because they are low-relief plains. Barrier flats can be overwashed repeatedly, and therefore they are very dynamic ecosystems.

Without a recent overwash event, the landward side of a barrier flat becomes what is known as an "early-succesional" environment. That is essentially an ecosystem that has just begun to establish itself after a destructive event.

Most plants can't survive inundation by salt water, so if overwash sediment and salt water comes sweeping over an area, it kills most of the plants. A thicket zone, a common early-successional landscape, has relatively small, herbaceous plants and shrubs that can quickly re-establish themselves after an overwash event.

If there hasn't been overwash for a long period of time, later-successional environments develop at the center of the barrier. These ecosystems can grow into forests with pine trees and large shrubs because they haven't been flooded by salt water and they are protected by the dunes.

On the bay side of the barrier there are marshes. In northern latitudes these are salt marshes, as opposed to mangrove swamps and other types of marshes found in different latitudes.

There are two types of salt marsh: low and high. The low marsh is almost constantly flooded, and the high marsh is flooded only at high tide. The high marshes are also called tidal flats because they are exposed during much of the tidal cycle.

Plants known as cordgrasses dominate these ecosystems because they can live in salt water. These areas are extremely important for all kinds of wildlife because there is water and land so closely intermingled. Fish spawn there, shellfish grow there, and birds nest and feed there. Furthermore, because the bay side marshes are protected from strong waves, they provide a sheltered area for animals to raise their young or find food. These marshes then lead into the bays that border the mainland.

 

Assateague Island

Assateague Island is one of the last undeveloped barriers along the Atlantic coast. It is frequented by many species of birds migrating along the Atlantic Flyway, and it provides habitat for the endangered piping plover. The island is part of the Western Hemisphere Shorebird Reserve Network.

Nearshore Troughs

Small fish and shellfish, such as mole crabs, can be found in the troughs of the nearshore zone.

Foraging Grounds

Beaches are foraging grounds for many types of shorebirds, such as gulls, terns, and piping plovers, that feed on small crustaceans and fish.

Grass on the Beach

American beachgrass (Ammophila breviligulata) is the predominant dune-building grass species along the mid-Atlantic coast, while sea oats (Uniola paniculata) is the most common species on the southeast and Gulf coasts.

Crucial Habitats

On Assateague Island, washover fans and barrier flats are crucial habitat for endangered species including piping plovers and seabeach amaranth.

Barrier Forests

Many types of mammals populate the forest environment of a barrier. Non-native species including horses and deer are found in this ecosystem on Assateague Island.

Salt Water Survivors

Cordgrasses can survive regular inundation by salt water, and they withstand burial from overwash sediments. Birds and mammals feed upon the grasses and the various forms of marine life that take shelter in them.