Fragile Barriers

Abarrier island is the first outpost of the land. On the ocean side the surf beats the sand beach, the waves arriving rhythmically, sometimes roughly, rolling in, unobstructed, across thousands of miles of open ocean. Behind the island—which may be only a few yards wide—lies a band of marsh and then the sheltered, brackish water of the bay, touching the mainland. The longest and most extensive chain of barrier islands in the world lines the eastern shore of North America. From New York to Florida to Texas, the islands fringe the continent, tucked in close to the mainland or standing off across miles of bay.

b&w photo, two horses fighting on beach

A barrier island is low and sandy, swept by winds. The key to its existence is a line of dunes: long hummocks running parallel to the shore just above the high tide line. A dune forms when windblown sand collects around clumps of salt-resistant American beach grass. As the wind dumps more and more sand on the grass, the plant pokes its tips higher; held together by the grass's branching root system, the dune rises 4, 5, 10 feet above the beach.

Dunes protect against storm tides. Without them, the sea will wash across the island, cutting new inlets and chewing away the shore. Under normal conditions, a barrier beach loses some of its sand to winter storms, but the sand is replenished from offshore bars the following summer.

A barrier island can be a place of extremes, baking hot in summer, frigid in winter, swept by the wind in all seasons. Still, life abounds. Some island creatures are obvious, at times even obtrusive: wild horses, whitetailed deer, foxes, raccoons, the myriad shore and marsh birds, horseshoe crabs, humans. Other life forms are more furtive. Ghost crabs live in holes dug in the sand near the dunes, emerging at night to search for prey. Sand hoppers, also active in the dark, spend the day dug into wet sand along the tide line. Marine worms, ghost shrimp, pea crabs, mole crabs, sea urchins, sand dollars, and coquina clams also populate the zone between low and high tides. Writes Rachel Carson in The Edge of the Sea, "Sand . . . forms a yielding, shifting substratum of unstable nature, its particles incessantly stirred by the waves, so that few living things can establish or hold a place on its surface or even in its upper layers. All have gone below, and in burrows, tubes, and underground chambers the hidden life of the sand is lived."

The turnover of biological materials is swift.

A dolphin, washed ashore by the tide, is pecked open at eyes, vent, and blowhole by gulls, worried by a wandering raccoon, picked apart by the gulls and crabs. A school of bluefish, hunting in the shallows beyond the surf, consumes scores of smaller fish, which in turn prey on vast numbers of even tinier swimmers. In the shallows—and, in still higher concentrations, behind the barrier in the quiet waters of the bay—the food pyramid broadens further, extending down to single-celled plants and animals: dinoflagellates, radiolaria, algae.

Even as its life constantly changes and redistributes itself, the barrier island is in a state of structural flux. Dunes, weakened by storms, are rebuilt by grasses and windblown sand. Heavy surf knifes through a narrow point, and two islands are born from one. The sea level of the ocean rises, and the barrier island reacts.

S/>ince the last ice age ended some 18,000 years ago, a gradual warming trend has been melting the polar icecaps, freeing water to the world's oceans. The tides have inched higher. Were a constant supply of sand available, a barrier island could maintain itself in place, building upward as sea level rises. Today, however, no new sediment is available, so the barriers respond by retreating: gradually creeping landward up the gentle incline of the coastal plain. They have moved from 100 to 1,000 feet, depending on the geographical location, in the last century.

When a barrier island withdraws naturally, key facets of the barrier system—the salt marsh, the band of trees that often runs down the spine of the island, the grassy flats behind the dunes, and the dunes themselves—regenerate further landward. The network of life accompanies the retreat. Writes Stephen Leatherman in Barrier Island Handbook, "The key to survival is a slow, gradual shoreline retreat to which all ecosystems involved can react." If the retreat is too slow, Leatherman says, the marshes and the island drown in the sea; too fast, and the bay fills in with sand, destroying the surrounding marsh.

Despite the barrier islands' instability, people have built on them. All along the coast, roads checkerboard the long, narrow islands. Houses and lawns cover grasslands, ditches drain the marsh, concrete sea walls replace the dunes, and jetties modify the shoreline drift of sand. All of these changes hinder a barrier island's ability to repair itself and to respond to a changing sea level.

Here and there, a barrier island remains in its natural state: It is privately owned, it is state or federal land, it is too small or too inaccessible for development.

Assateague Island is such a place. Owned and administered by the federal government and the state of Maryland, Assateague is 37 miles long and from one quarter to two and a half miles wide, totaling 19,000 acres. The island parallels the Maryland-Virginia shore. Immediately to the south lies Wallops Island, controlled by the National Aeronautics and Space Administration (NASA) and largely undeveloped; to the north, across a quarter-mile inlet, is Fenwick Island, blanketed by the town of Ocean City, Md.

In the early 1960s, the northern end of Assateague was slated for development. Streets had been plotted, a road paved, lots sold, and cottages were springing up. Restaurants, hotels, and shopping centers were planned. The National Park Service, reviewing lands for a possible national seashore, ruled out northern Assateague, calling it "the site of one of the largest seashore developments along the Atlantic coast."

On March 6, 1962, a storm curled up the eastern seaboard. It battered Cape Hatteras and Virginia Beach and swept in on Assateague. On Chincoteague Island—a landward island protected by the barrier Assateague—water rose against the sides of houses and deposited fishing boats on Main Street. On Assateague itself, a 30-foot surf—storm waves coupled with high spring tides—lashed the dune line and breached it. High winds and waves ripped houses off their pilings, destroying all but the sturdiest, and washed out and buried the road.

In 1965, after two years of discussion, heated debate, and political maneuvering, President Lyndon Johnson signed a bill creating Assateague Island National Seashore. The federal government began buying private land.

Each year, about two million people visit Assateague. They camp, collect shells, fish in the surf, canoe the bay, watch the gulls and terns that wheel overhead. In the fall, hunters search for deer and waterfowl.

Scientists also treasure the unspoiled environment. In 1983, they were studying peregrine falcons, ghost crabs, beach erosion, and brackish ponds. Plant hoppers, least terns, and fish were also under scrutiny. A team of Army researchers was monitoring tethered goats for mosquito-borne diseases, and one behavioral scientist was said to be running a motorized toy tank, draped with a raccoon skin, up and down the beach, noting the response of nesting birds.

Penn State researchers are busy on Assateague, too. Ron Keiper works on wild horses, Bill Dunson studies snapping turtles, and Al Guber and Rudy Slingerland explore barrier beach geology. Other Penn Staters monitor the kinetic chemistry of air, sea, and sediments; the ecology of bryozoans; eel and crab behavior; and the populations of Sika and whitetailed deer. In May 1983, Research/Penn State sent me to interview Keiper, Dunson, and Guber and Slingerland about their projects. Articles on the research follow.

Last Updated June 01, 1984