For example, some of our lowest tides occur at low tide in the winter with a strong northwest wind. There are many tidal flats that are exposed only at this time of year.
And the highest tides often occur at high tide with a southeasterly storm. Vegetation Cordgrasses of the Spartina genus are the most prominent salt marsh vegetation. Flooding frequency how often and duration for how long see Hydrology and the salinity level are the most important variables that control the kinds of plants that occur in the salt marsh.
In the high marsh, saltmeadow cordgrass might be the most common grass, whereas in the lower marsh, saltmarsh cordgrass is more common. Additional vegetation includes saltgrass, saltmarsh bulrush, and needlegrass rush among other. Animals Typical animals include herons, egrets, ibises and other wading birds that feed on the fish, shrimp, crabs and other invertebrates found in the wetlands. Shorebirds and waterfowl are abundant.
The American alligator feeds on fish, snakes, turtles, frogs, muskrats, nutria, swamp rabbits, rats and anything else it can catch. Bobcats, coyotes, raccoons, skunks, mink and river otters also hunt in the marshes. Threats Estuarine wetlands are threatened by land subsidence and relative sea level rise that causes marshes to drown and be converted to open water. Subsidence and dredged channels and canals allow saltwater to intrude inland into fresher areas causing vegetation changes.
There is direct marsh loss to dredging, filling, and spoil deposition caused by various kinds of development. Dredging activities cause increased water turbidity that threatens seagrasses. Dams on the rivers that supply freshwater and sediment to the bays have altered the fresh water inflow processes that maintain the estuaries.
Runoff pollution from urban and agricultural sources, and oil and chemical spills damage vegetation and animals. Since then mids, the area of salt and brackish marshes on the Texas coast has decreased by more than eight percent; a net loss of more than 31, acres.
Much of the loss was due to the construction of dredge-spoil compartments along the Intracoastal Waterway and other ship channels. Even in south Texas, black mangrove is subject to periodic severe dieback caused by freezing temperatures.
Another, more permanent threat is development in the intertidal zone for resorts, marinas, beach houses and boat docks, roads and causeways, canals and ship channels, and so on. The Laguna Madre is being filled in with wind-blown sand from Padre Island.
The sandy flats that separate the upper and lower Laguna is an area called the Land-Cut; a name that relates to the excavation of the Gulf Intracoastal Waterway. This region of the Laguna filled with wind-blown sand perhaps years ago. Shrimp are just one species of fish and shellfish that are dependent on estuarine habitats for at least part of their life cycle. Ecological Functions and Human Values Many economically important finfish and shellfish use estuarine wetlands during at least part of their life cycles.
The wetland habitats are used for spawning, as nursery areas, and for foraging. Shrimp, crabs and oysters all depend upon estuarine habitats. Predatory fish like red and black drum, seatrout, and southern flounder are supported by estuarine invertebrates and forage fishes like bay anchovy, striped mullet, bay silversides, killifishes and gobies.
Seagrass beds provide feeding habitat for game fish, migratory waterfowl especially redhead ducks , and sea turtles. They serve as nursery areas for fish, crabs and shrimp.
These fish and wildlife habitats help support economically important commercial and recreational fishing, hunting and birdwatching industries. Serving as vital shelter for birds, the diverse salt marsh plants also provide food for marine life. Plus, by buffering waves, trapping sediment, and absorbing rainwater, marshes help prevent coastline erosion , protect water quality, and reduce flooding.
Located in the intertidal zone of tropical coastal areas and estuaries, mangrove trees cannot grow in areas with freezing temperatures.
Like marshes, nutrient-rich mangroves provide shelter and nourishment to their habit residents, including fish, crabs, shrimps, manatees, sea turtles, and hundreds of bird species that migrate and nest in mangrove forests. Thanks to their dense tangle of roots and leaves, mangrove trees help filter out salt, replace lost sediment, and lessen the impact of waves, thus protecting shorelines from erosion and storm damage.
This mass of roots visible above water enables mangroves to manage high and low tides every day. Skip to main content. You are here Home. Between the levees and tidal creeks are marsh flats, which contain pools and salt pannes. Salt pannes are shallow depressions that contain very high concentrations of salt.
Pannes retain seawater for very short periods of time. When the seawater evaporates, the salts remain and accumulate over many tidal cycles. Glasswort, a plant tolerant to very high salt concentrations, is one of the only organisms able to survive in salt pannes.
Pools are generally deeper than pannes, and retain water all year long. Salt-marsh snails and green crabs are some of the creatures found in pools scattered across the marsh. Low-lying areas of the marsh are often covered with large, flat expanses of mud called mud flats. Composed of fine silts and clays, mud flats harbor burrowing creatures including clams, mussels, oysters, fiddler crabs, sand shrimp, and bloodworms. Salt marshes are salty because they are flooded by seawater every day.
They are marshy because their ground is composed of peat. Peat is made of decomposing plant matter that is often several feet thick. Peat is waterlogged, root-filled, and very spongy. Because salt marshes are waterlogged and contain lots of decomposing plant material, oxygen levels in the peat are extremely low—a condition called hypoxia. Hypoxia promotes the growth of bacteria which produce the rotten-egg smell that is attributed to marshes and mud flats.
Salt marshes are covered with salt-tolerant plants, or halophytes, like salt hay, black rush, and smooth cordgrass. However, these plants do not grow together in the same area.
Marshes are divided into distinct zones, the high marsh and the low marsh. The difference in elevation between these two areas is usually only a few centimeters, but for the plants that inhabit each of these zones, a few centimeters makes a world of difference. The low marsh floods daily at high tide.
The high marsh usually floods about twice a month during very high tides associated with new and full moons.
0コメント