Golden Isles

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Marshlands

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"...By a world of marsh that borders a world of sea. Sinuous southward and sinuous northward the shimmering band of the sand beach fastens the fringe of the marsh to the folds of the land."

In the 1870s, Georgia poet Sidney Lanier was inspired to write The Marshes of Glynn as he stood and beheld the vast marshlands that embrace the Golden Isles.

These marshes are undoubtedly one of the area's most remarkable sights.  But they do much more than dazzle those who view them.  The salt marshes are a fragile yet enormously productive ecosystem, considered as some of the most extensive and productive marshlands in the world.

Georgia’s coastal marshlands encompass approximately 378,000 acres in a four to six mile band behind the barrier islands.  Thriving in the waters of the estuaries, these marshes have been identified as one of the most widespread and thriving marshland systems in the United States.  There are nearly 400,000 acres of coastal marshlands in Georgia which represent one third of all remaining marshlands along the entire eastern coast of the United States.

Productive almost beyond comprehension, this salt marsh grass is responsible for the continuation and survival of the intricate balance of nature within the estuarine ecology. Producing nearly 20 tons to the acre, it is four times more productive than the most carefully cultivated corn.  Georgia’s salt marshes produce more food energy than any estuarine zone on the eastern Seaboard.

 

Truly the tid

e is the life blood of the marsh bringing its subsidy with each coming and going.  The incoming tide nourishes and feeds the grasses of the marsh. The outgoing tide harvests its products and, through the tidal energy, breaks down the grasses and feeds the resources to the sea.  Coastal tides average approximately six and a half feet in the marshes but exceed ten feet during high spring tides.

As the grasses die and decompose, nutrient byproducts are produced and taken by the outgoing tides and begin to feed an ever growing number of organisms until all forms of marine life in the estuary have benefitted. These minute, decaying particles feed small fish, plankton, oysters, shrimp, clams and crab. The marsh serves as a nursery ground for the growing juveniles of fish and shellfish, and these fish in turn support larger fish and so the cycle goes on and on. In addition, the stems and grass provide refuge for many adult animals in estuaries where salt and fresh water mix.

One of the most important roles marshes and estuaries play is that of a tertiary treatment facility for mineral nutrients from man’s systems. The marsh grass and sediments act as both a sink and a pump, meaning that large amounts of nutrients come into the estuary from the land and sea.  Once in the marshlands, the nutrients are quickly stored and become available to other organisms.

Additionally, our salt marshes act as buffers against offshore storms. Without them, hurricanes and northeasters on the Atlantic coast would do a lot more damage.  The destructive fury of large storm-spawned waves and tides is greatly reduced by their passage across the marsh. The grass absorbs most of the energy, which lessens the damage that can be done.

Intertidal Mud Flats

Intertidal mud flats are located along the edges of the salt marsh. This harsh habitat is covered by water at flood (high) tide and exposed to the scorching sun at ebb (low) tide.  It consists of a soggy substrate (soil) made up of clay and silt that is deposited during slack tide. Slack tide is the brief period between flood tide and ebb tide during which the water is not flowing in or out but is still.  Only the upper layers of this muddy substrate contain oxygen. The deeper layers contain decaying organic matter that gives off a hydrogen sulfide gas that causes a brief rotten egg smell at low tide.

Only a few plants and animals live in the tidal flats, but those that do are an important food source for larger animals.  Phytoplankton and algae grow on the surface of the mud (giving it a greenish tint) and attach to hard surfaces such as old shells or logs.  Insects breed in small pools and the larvae feed on algae and zooplankton.  Buried animals such as cockles, whelks, amphipods, lugworms and fiddler crabs eat microorganisms that are trapped in the mud.  When the tide comes in, phytoplankton, algae and zooplankton serve as the food source for filter feeders (oysters, clams, mussels, barnacles) and several types of worms including the parchment tube worm.  Shrimp and crabs eat worms, while crabs and flounder eat shrimp. Also at high tide, organisms that always live in the water come in to feed.  Blue crabs and several species of hermit crabs scavenge for food while fish such as the mummichug, silversides, spot and croker feed on insect larvae, zooplankton and small fish.

When the tide goes out, the muddy substrate is exposed and fiddler crabs come out of their burrows and sift through the mud for food while periwinkle snails eat algae off the surface of the mud.  Mud snails scavenge the surface, eating both living and dead organisms.  Wading and shore birds like egrets, clapper rails, gulls and sandpipers come in to eat the snails, worms, fiddler crabs or any other floating or crawling animal.  Oyster catchers feed off the oysters, mussels and clams. Raccoons also venture onto the mud flat to feed on whatever they can find.  The animals that live in or on the mud flats are important food sources for larger animals and any disturbance of this harsh but fragile habitat could have grave consequences for the food chain.

Courtesy of the Sapelo Island National Estuarine Research Reserve
www.sapelonerr.org
Written by Margaret Olsen