Salt Marsh Ecology
Georgia has the second largest amount of salt marshes in the United States.
Twice a day, the tides along the coast rise and fall 6 to 8 feet. The tide allows unique ecosystems to exist, such as the important salt marshes. On the southeastern coast of the United States, salt marshes take shape in shallow areas between barrier islands and the mainland.
The one hundred miles of Georgia’s coast has approximately one-half million acres of marshland, each marsh ranging from 4 to 8 miles wide. Georgia has the second largest amount of salt marshes in the United States and the marshland on Georgia’s coast makes up an estimated one-third of all the salt marshes on the east coast.
The marsh is a harsh environment for wildlife. The temperature can quickly change with the shifting tides. The inconsistent influx of salt water causes the land to have irregular exposure to air and salt water. This makes it difficult for species to inhabit the marsh full time. Although the marsh is not home to many permanent residents, various land and aquatic species visit the marsh in order to feed and take shelter and the marsh’s shallow tidal water is home to the young of many marine species before they return to the open sea.
Ecological Zones of the Marsh
The marsh can be divided up into ecological zones based on the time and depth of the tides.
The levee marsh is the habitat on the banks of tidal creeks. The soil is regularly bathed in seawater and the constant supply of water helps the area maintain consistent salinity and temperature. There is a continual flow of nutrients that supports vegetation on the banks, such as smooth cordgrass that can grow up to six feet.
Beyond the levee is the low marsh. The low marsh zone makes up the majority of the southern marshlands. It is flooded for several hours of the day when the incoming tides overflow the banks of the small surrounding creeks. The shallow seawater gradually drifts over the black marsh mud and the sun shines directly on the water. The sun increases the water temperature and large quantities of organic matter are suspended in the water and mud, thereby reducing the amount of oxygen available to living organisms.
As the temperature of the water increases, it evaporates and leaves behind large amounts of salt causing a rise in salt concentration. In the low marsh, the cordgrass grows between 1 and 3 feet high. The irregular and transient conditions make the low marsh a poor living environment compared to the levee marsh.
After a slight rise in elevation, the low marsh gradually transforms into high marsh. The high marsh is characterized by a sandy soil that is barely covered with water during high tide. The surface is covered for an hour or less each day so the soil surface is exposed to air for long periods of time. Much of the surface water evaporates, which creates a high concentration of salt. The high salt concentration makes it difficult for plants to live in the high marsh. For example, the cordgrass is very small, 3 to 12 inches in height, or not present at all.
Instead, salt-resistant species such as glasswort, saltwort and salt grass thrive in the high marsh. Bare sandy areas, known as “salt pans,” occur where the salt concentration has become great enough to prevent all plant life. The levee and low marshes are populated with species like the mud fiddler crabs, purple marsh crabs, oysters, ribbed mussels, polychaete worms and snails. The high marsh is home to sand fiddlers and wharf crabs.
A zone known as the marsh border is habitat to plant communities. At a higher elevation than the high marsh, there are few seawater floods. The salt concentration is very low without the seawater rushing in and with the freshwater rain and runoff from nearby uplands. At an even higher elevation, additional plants like marsh elder grow. In depressions with small amounts of water, the largest of the fiddler crabs, the brackish-water fiddler, can be found.
Cabbage palms signify a transition community from the marsh to the woody vegetation that leads toward the maritime forest. The same border communities are seen surrounding the marsh islands or hammocks. This transition community is an ideal area for mammals, birds and reptiles to feed. In some areas, there is a steep increase in elevation and instead of a transition community the forest sits on the edge of the marsh.