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Project WILD Teacher Resource Guide

Barrier Islands

Physical Landscape
Surely the crown jewels of the Georgia coast are the undeveloped barrier islands.  Due to a fascinating history of land ownership and farsighted conservation laws (The Marsh Protection Act) Georgia has the least disturbed coast on the eastern seaboard.

Our coastline is roughly 110 miles long, stretching from the Savannah River in the north to the St. Marys River in the south.  The soils are typically sandy and habitat disturbances include wind, waves and tides. The Georgia Coast enjoys a subtropical climate with long hot summers and mild winters during which temperatures rarely fall below freezing. The coast receives 30-50 inches of rain annually. Thunderstorms generate most of the summer rainfall as the Bermuda High Pressure system dominates the region keeping low-pressure storms away.

There are 8 clusters of barrier islands off the coast of Georgia, four of which are accessible by car (Tybee, Sea, Jekyll, and St. Simons Islands).  The remaining islands are more difficult to reach but are well worth the effort because they are much less developed than the accessible islands.  These island clusters protect the mainland and salt marshes from the constant onslaught of wind and waves.

Barrier Islands are, by their very nature, in a state of constant change, reshaped by the ongoing action of wind, currents and tides.  Depending on the relative strengths of these three forces, barrier islands will assume radically different shapes.  Even a cursory glance at a map illustrates the difference between the barrier islands of Georgia and those of the Carolinas.  Georgias Islands are generally rectangular in shape in sharp contrast to the narrow linear islands forming North Carolinas Outer Banks.

Due to the location of Georgia in the heart of the South Atlantic Bight, a large indentation in the southeastern coastline stretching from Cape Hatteras in the north to Cape Canaveral in the south, and the continental shelf far off shore, Georgias coastline is well protected from major storms, waves and currents.  This protection, coupled with a fairly high tide range (7-9 feet), makes the daily tidal fluctuations the most important shaping force on our islands.  Tidal currents generally run perpendicular to the coastline, forming wide, short islands from the sands and silts of the coastal sediments.  These wide, short islands are called mesotidal islands. In sharp contrast, the North Carolina coast is exposed to the brunt of many Atlantic storms and has a much smaller tidal range than Georgia. This situation generates a strong longshore current running parallel to the coast that creates long narrow islands that are called microtidal islands.

The short rectangular islands of the Georgia coast are more stable than the islands of North Carolina and have developed more extensive maritime forests.  Our islands have been in roughly the same position for the last 4 -5,000 years.

The actual formation of Barrier Islands requires a gently sloping continental shelf and a rising sea level.  These two parameters were met in Georgia over the last 20,000 years, as sea levels rose from melting glacial ice at the end of the last glacial period. Rising sea levels surrounded and isolated existing dunes, forming islands.  Sediments carried downstream settled in behind these islands to form the rich salt marshes of the tidal zone.

The typical form of our barrier islands includes a wide beach facing the open ocean, with slightly elevated dunes above the high-tide line.  Behind and protected by these dunes is the maritime forest of the interior.  Vast expanses of salt marsh stretch between the islands and mainland with scattered hammock forests protruding from the otherwise unbroken waves of saltmarsh cord grasses.

Habitat Highlight: Beaches
Constant wave action prohibits the establishment of plants along active beaches, and a quick glance might suggest a lifeless boundary between sand and water.  Closer observation however reveals a more complex reality.  Shorebirds continuously probing into the sand provide evidence of an invisible host of invertebrates beneath the uniform sands.

Dark cylinders reminiscent of chocolate ice cream sprinkles surround the opening of Ghost Shrimp (Callianassa sp.) holes in the low tide zone.  Ghost Crab (Ocypode ceratophthalmus) tracks and holes are also evident to the careful observer. These are white crabs up to 3 inches wide that scavenge along the upper beaches at night.  The high-tide line of seaweed and driftwood is often hopping with Sand Fleas (Orchestia agilis) and provides cover for the elusive Piping Plover (Charadrius melodus, an endangered species).  Further evidence of life includes washed up coral fragments, shells, Sand Dollars (Dendraster excentricus) and seaweed.

Glancing over the Atlantic Ocean itself often yields diving terns and pelicans, rafts of ducks and flocks of shorebirds.  In winter Northern Gannet (Morus bassanus) may be seen diving from up to 50 feet above the surface. Dolphins are also commonly seen at points along the Georgia Coast.

Habitat Highlight: Dunes
As you walk inland from the beach towards the maritime forest, you will pass through distinct vegetative zones as the effects of direct wave action, salt-spray and wind diminish.  The first plants you meet are the hardiest most salt tolerant species such as Sea Oats (Uniola paniculata), Prickly-pear Cactus (Opuntia sp.) and Beach Morning Glory (Ipomea stolonifera). These plants can survive the harsh sandy landscape. They play an important role in stabilizing the Dunes with their extensive but shallow root systems.  Plant cover and diversity generally increase as you move inland from the fore-dunes, across the dune meadow to the more stable back dunes.  Wax Myrtle (Myrica ceriferus) shrubs will often form dense thickets on the back-dunes, both stabilizing the soil and providing habitat and food for wildlife such as wintering Yellow-rumped Warblers (Dendroica coronata).

During storm surges, waves may break through and obliterate the protective dunes carrying saltwater inland.  These washover events can form saltpans that are highly resistant to plant establishment.  Few environments exhibit such an obvious struggle between plants and natural disturbances as the Dunes, where plants constantly work to stabilize and winds and water to destabilize.

Habitat Highlight: Maritime Forest
Crossing into the back dunes and beyond you will enter the realm of the maritime forest. The maritime forests of the southern coast are as unique and enchanting as any other forest in the United States.  The intricately gnarled Live Oaks (Quercus virginiana) cloaked in Spanish Moss (Tillandsia usneoides) and Resurrection Fern (Polypodium polypodioidies) and surrounded by Saw Palmetto (Serenoa repens) seems to be an anachronistic remnant of a slower and quieter past.  The spreading canopy of Live Oak, Southern Pine (Pinus sp.), Southern Magnolia (Magnolia grandifolia) and Cabbage Palm (Sabal palmetto) temper the harsh forces of wind and water that assault the dunes and beaches.  Temperatures and winds are moderated under the tree canopy, which increases moisture levels and allows a dense understory of herbs and shrubs to develop.

Spanish Moss and Resurrection Fern are both epiphytes, plants that live on other plants entirely independent of the soil.  Typically epiphytes require humid environments where they can absorb moisture directly from the atmosphere, so they are more common in the humid tropics than temperate regions.  In the understory dense clusters of Saw Palmetto provide excellent hiding places for Eastern Diamondback Rattlesnakes (Crotalus adamanteus), Georgias most dangerous snake, which hunts rabbits and other mammals across the Coastal Plain and islands.
Habitat Highlight: Salt Marshes
A combination of heat, biting insects and the odor of decomposing vegetation can make salt marshes a challenging habitat to enjoy in the summer.  During the cooler times of the year however, Salt Marshes are great places to visit, affording good views of many birds and other wildlife.

Georgia contains one third of the Salt Marshes along the entire eastern seaboard.  Vast expanses of marsh grasses live between the mainland and the protective barrier islands all along the Georgia coast.  The lack of plant diversity belies the incredible biological importance of coastal Salt Marshes.  They are some of the most productive systems on earth, producing vast amounts of biomass annually. They provide important habitat for a wide range of fish, shellfish and bivalves, many of which form important staples of the human diet.

Many species of birds such as Great Blue Herons (Ardea herodius), Bald Eagles (Haliaeetus leucocephalus), Clapper Rails (Rallus longirostris) and various ducks and sparrows use these coastal marshes seasonally.  Raccoons (Procyon lotor) regularly hunt the edges of salt marshes leaving their characteristic handprint tracks as evidence of their nocturnal forays.

Salt Marshes form behind barrier islands where they are protected from the relentless wind and waves of the ocean.  They also form along estuaries where rivers enter the ocean.  Salinity of these marshes decreases as one moves farther inland, and one eventually finds an entirely fresh water marsh that is still tidal, as the fresh water backs up behind the tidal bulge of salt water closer to the coast.  This salinity gradient offers a wide range of habitats for plants and animals.

Salt Marshes exhibit some of the harshest environmental conditions of any Georgia ecosystem.  As the tides ebb and flow, temperature, salinity and water levels drastically change.  Plants and animals must be able to survive these environmental fluctuations if they are to last in the Salt Marsh.  The star of the salt marsh is Cord grass (Spartina alterniflora), which is well adapted to surviving the rigors of life in the inter-tidal zone.

Perwinkles (Littorina sp.) are salt-water snails that crawl up and down the Spartina, grazing on algae that grow on the leaves.  Some suggest that these snails actually weaken the Spartina, making them more susceptible to environmental stresses.  This has been raised as one idea explaining why many areas of coastal marsh are dying off.  (To view this die-off, look at the Jericho River on I-95 just south of Savannah).

Tidal creeks and streams meander through the marsh draining and flooding the salt marshes twice each lunar day.  Though tides create a harsh environment, they also provide the sustaining nutrients and carry wastes from the entire system.  Along these channels Oysters (Crassostrea virginica), Ribbed Mussels (Geukensia demissa) and Blue Crab (Callinectes sapidus) can be found.

Habitat Highlight: Reefs
Probably the least known habitat in Georgia, and certainly the hardest to visit, is the reef ecosystem off the Georgia Coast.  The largest example is called Grays Reef, and it is located 17 miles offshore from Sapelo Island.

If you imagine the Georgia (South Atlantic) Bight, the vast majority (> 95%) of the seafloor is composed of loose sediments that provide very little habitat for marine species.  Any hard substrate on the sea floor allows animals and plants to attach, and forms an ecological island in an otherwise barren under water plain.  Rocks or shipwrecks can provide a hard surface for reef formation.

Ridges of sedimentary rock exposed on the sea floor form Grays Reef.  Though these ridges only rise about 6 feet off the sea floor, they form a critical substrate for soft corals and sponges to grow, attracting large numbers of marine fish, mammals and even reptiles.  Burrowing marine worms dig through the soft rock, creating even more habitat.  Due to the location of Grays Reef, there are both tropical and temperate species found there.  Temperate fish such as Sheepshead (Archosargus probatochephalus) share space with tropical reef fish, such as Angel Fish (Centropyge sp.) and Butterfly Fish (Chaetodon sp.).

Several endangered species can be found at Grays Reef.  During the calving season, Atlantic Right Whales (Eubalaena glacialis) have their young within the sanctuary and endangered Loggerhead Sea Turtles (Caretta caretta) feed on the sponges, whelks and crabs found on the reefs. Grays Reef is so critical for marine wildlife that it was designated a National Marine Sanctuary in 1981.

Attempts have been made to increase the amount of reef habitat off the Georgia coast.  Divers have long known that shipwrecks are often great places to observe marine animals and plants, as the physical structure of the wreck provides habitat.  This knowledge has led to the intentional sinking of ships, subway cars and artificial cement reef structures to provide habitat for fish and other species.  Marine plants and animals rapidly colonize these artificial reefs.

Key Animals: Manatee
Manatee (Trichechus manatus) are fascinating, large endangered marine mammal that can be found off the Georgia coast between March and November.  It is one of only 4 Sirenians (order Sirenia) in the world, a group of aquatic mammals that are closely related to elephants.  Generally it is found in shallow coastal waters and up tidal rivers.  Manatees eat Spartina (cord grass) as well as other emergent vegetation.  The Manatee primarily stays in Florida though they do swim north to Georgia in spring and summer.  They often bask near the surface, leading to frequent boat collisions and associated mortality.

Northern Right Whale
The Northern Right Whale (Eubalaena glacialis) is Georgias state marine mammal, and is the most endangered whale in the world.  Estimates put their population at around 350-400 individuals.  The Right Whale is a baleen whale, meaning that it feeds by filtering vast amount of water through hundreds of baleen bristles hanging from its top jaw.  Right Whales generally feed on tiny zooplankton called Calanoid Copepods off the coast of Cape Cod and Nova Scotia, and do not feed during their southward visit to Georgia and Florida where they calf.

The Right Whale received its name from whalers because of the ease and profitability of hunting them.  Right Whales are large and produce huge amounts of blubber. They are also slow and float once they are killed.  This combination made them easy prey for early hunters, and their numbers rapidly declined until they were first protected in 1935.

Today the most serious threats to the Right Whale are entanglement in fishing nets and collisions with ships.  A communications network has been established to alert commercial vessels of the presence of Right Whales so that collisions can be averted.

Loggerhead Sea Turtle
The Loggerhead Sea Turtle (Caretta caretta) is the most common of 5 sea turtle species that use the coast of Georgia and is the only one that regularly lays eggs on our beaches.  The other species i

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