Tidal marshes, a type of wetland, can be found along protected coastlines in middle and high latitudes worldwide. They are most prevalent in the United States on the eastern coast from Maine to Florida and continuing on to Louisiana and Texas along the Gulf of Mexico. Some are freshwater marshes, others are brackish (somewhat salty), and still others are saline (salty), but they are all influenced by the motion of ocean tides. Tidal marshes are normally categorized into two distinct zones—the lower or intertidal marsh, and the upper or high marsh.
In saline tidal marshes, the lower marsh is normally covered and exposed daily by the tide. It is predominantly covered by the tall form of smooth cordgrass (Spartina alterniflora). The saline marsh is covered by water only sporadically, and is characterized by short smooth cordgrass, spike grass, and black grass (Juncus gerardii). Saline marshes support a highly specialized set of life adapted for saline conditions. Brackish and fresh tidal marshes are also associated with specific plants and animals, but they tend to have a greater variety of plant life than saline marshes.
Functions & Values
Tidal marshes serve many important functions. They buffer stormy seas, slow shoreline erosion, and are able to absorb excess nutrients before they reach the oceans and estuaries. High concentrations of nutrients can cause oxygen levels low enough to harm wildlife, such as the "Dead Zone" in the Gulf of Mexico. Tidal marshes also provide vital food and habitat for clams, crabs, and juvenile fish, as well as offering shelter and nesting sites for several species of migratory waterfowl.
Pressure to fill in these wetlands for coastal development has lead to significant and continuing losses of tidal marshes, especially along the Atlantic coast. Pollution, especially near urban areas, also remains a serious threat to these ecosystems. Fortunately, most states have enacted special laws to protect tidal marshes, but much diligence is needed to assure that these protective measures are actively enforced.
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