Salt Marsh

Green marsh grass flooded with brackish water
The high tide floods the salt marsh, bringing nutrients and animals in to forage. As the tide goes out, animal wastes are flushed out.

NPS Photo/Audrey Bohl

Along the coast of Georgia, the salt marsh habitat covers a huge area. This is because Georgia has a high tidal range (difference between high and low tide) and a low elevation along the coast. The salt marsh plays an important role in the ecosystem by providing habitat for animals, reducing floods, and filtering the water.
 
low tide exposes oyster reefs in the salt marsh
As the tide goes out, oyster banks are exposed. Oysters are filter feeders and play an important role in cleaning the water that passes through the marsh.

NPS Photo

Cumberland Island National Seashore has 9,341 acres of salt marsh. A marsh is a wetland where the main vegetation is non-woody plants, like grass. There are both fresh and salt water marshes. In a salt marsh, salt water floods the area at high tide. Elevation of the land and height of water in the marsh varies, allowing for a diversity of plants and animals. Because many plants cannot tolerate much salt, the salt water inundation limits what plants can live there.

The Cumberland Island salt marshes are found on the western side of the island, protected from the force of the waves by the main island. It is bordered by the maritime forest. A small transition zone separates the forest from the marsh. This is referred to as the marsh border. During large storms and very high tides the marsh border gets flooded by salt water, so the plants are salt tolerant. Cedars, palms, palmettos and groundsel tree are commonly seen in this area.

The tide plays a vital role in the salt marsh. It brings in nutrients, oxygen, and water, as well as animals. Few animals actually live in the marsh. Most are visitors looking for food or shelter. Many enter the marsh as plankton (microscopic drifters) and leave as adults. Crabs and shrimp are good examples of this. Other organisms enter to stay, like periwinkle snails and oysters. Each has adaptations to help them survive in this changing environment.
 
Fiddler crabs foraging in the marsh grass
Fiddler crabs play an important role in the salt marsh. They help to decompose dead organic matter and their burrows allow oxygen into the mud to aid bacterial decomposition. They are also tasty treats for many animals

NPS Photo

The actual marsh has two major zones - the high and the low marsh. These two areas are delineated by the vegetation type, which is an indication of the daily water coverage. The high marsh is covered with water only at the highest tides, which occur when the moon is new or full and during stormy weather. It has sandy soil and a high diversity of plants. These include sea oxeye, glasswort or sea pickle, needle rush and saltwort.

The low marsh is flooded with salt water for 6-8 hours per day. There is only one kind of plant that has adapted to survive this - Spartina alternaflora (smooth cordgrass), making it a true, natural monoculture. This grass has several adaptations that allow it to live in the salt marsh. As it absorbs water through its roots, a membrane filters out most of the salt, allowing mostly fresh water to enter the plant. Extra salt is collected by a gland in the leaves and then excreted through special pores. You can sometimes see the salt crystals on the stem and leaves of the Spartina grass.

The soil is dark and squishy in the low marsh. Bacteria are hard at work decomposing dead plant matter and turning it into nutrients for plants and planktonic creatures. Sometimes this muck can produce a distinctive, musky smell due to the decomposing plant matter.

Tidal creeks wind through the sea of grass in the salt marsh. The tidal creek is the life blood of the marsh. It brings nutrients, oxygen and water into the marsh and then carries wastes away, just like the blood vessels of the human body. Bordering the tidal creeks is a raised area called a levee. It is formed from tidal deposits as the waters flow over the bank. Friction causes the water to slow and drop the sediment load which is how the levee is built.

The salt marsh is one of the most productive ecosystems in the world. Much of the seafood that we eat start it’s life in the protection of the salt marsh. By preventing flooding, cleaning water and providing habitat for animals the salt marsh provides vital ecosystem functions that make it important to preserve.

Last updated: December 14, 2018

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