A river of grass swaying in the breeze where the land meets the water, salt marshes are among the most productive habitats found within the Indian River Lagoon. Because they exist in areas which man has steadily developed or altered over many years, they are also among the most threatened habitats.
Salt marshes are coastal wetlands which
develop along low-energy estuary shores. There is usually a pronounced
tidal fluctuation within a salt marsh and the vegetation which occurs here
exhibits various degrees of salt water tolerance. The zonation of the
various grass species which form the basis of the salt marsh community is
highly dependent on each species' tolerance to inundation (partial
submergence) by salt water. Smooth cordgrass, shown here at the water's
edge, is the species most tolerant to salt water. It is usually found
closest to the water. This species can grow quite tall - up to 2.5 meters
(more than 8 feet).
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Smooth cordgrass |
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Farther back from the edge of the water is
saltgrass. This species usually grows in dense colonies, and forms thick
mats of roots and underground stems called rhizomes. Saltgrass only grows
to around 75cm tall (about 2.5 feet), not as tall as cordgrass. The
45-degree branching angle of the leaves (see bottom photograph) may aid in
the identification of this species.
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Saltgrass |
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Occurring in the higher marsh areas - further away from the water's edge -
vast stretches of black needle rush can be seen. The brown and gray field
of grass in this aerial photograph is composed of needle rush. The common
name of this species comes from the sharpened stem tip which is capable of
puncturing a person's skin.
The use of helicopters to survey the salt
marshes of the Indian River Lagoon is probably the best way to get to
areas of the marsh inaccessible by foot. A helicopter can easily take off
and land almost anywhere on the marsh, allowing biologists the chance to
study habitats rarely visited by people.
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In addition to the various grass species found here, the salt marsh is
also home to a variety of other plant species. Two commonly encountered
species are glasswort and saltwort. These species possess succulent body
parts - their leaves and stems - which function as water storage sites. In
the summer these species exhibit luxuriant growth and are bright green in
color. In the fall the glasswort begins to turn redddish in color, due to
the presence of plant pigments which are usually masked by the green
pigment chlorophyll. This is the same reason leaves change color in many
parts of the country during the fall months. In the top photograph, the
glasswort is just beginning to change color. These species are edible, if
a little salty, and can be used by more adventurous eaters as a tossed
salad ingredient.
 Glasswort Salicornia virginica |
 Saltwort Batis maritima |
These aerial photographs show one of the prominant features of the salt marsh - small, isolated pools of water - occurring in areas of low elevation. These depressions are called pannes, or potholes. Pannes form when surface layers of accumulated organic debris, known as peat, are decomposed by microorganisms like bacteria and fungi. Monthly high tides, rain and runoff from tidal creeks fill these pannes with water. Much of the time, however, the pannes are dry. Smaller, shallower pannes are particularly susceptible to drying. The photograph, on the right, shows a small panne which has dried up.
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Since the pannes undergo regular periods of flooding and drying, they are an ideal breeding ground for tidewater mosquitos. Furthermore, since the pannes are not usually directly connected with the rest of the lagoon, mosquitofish and other predators of mosquito larvae cannot get into the pannes to eat the larvae. The use of a mosquito control technique called rotary ditching has been shown to be a good way of controlling mosquitos in the marshes. In rotary ditching, small channels are dug which connect the pannes to the rest of the lagoon (see left photograph above). Natural predators can now get into the pannes to eat the larvae. Rotary ditching is a mosquito control technique which is much less damaging to the natural functioning of the marsh than the older technique of marsh impoundment.
| Impounding a marsh is a
way of artificially maintaining a high water level in the marsh.
This prevents breeding of tidewater mosquitos. It also disrupts
the natural functioning of the salt marsh by cutting it off from
the rest of the lagoon system.
Impounding marshes cuts lagoon organisms off from the important food supply provided by highly productive salt marsh vegetation and the animal species associated with them. It also prevents juvenile fish and shellfish from using the marsh as a refuge and nursery area (see Seagrass Habitat section of the program for more information). Finally, isolating salt marshes from the rest of the lagoon destroys the natural filtering abilities of marsh vegetation. This plant life takes up excess nutrients and pollutants from stormwater runoff before it enters the lagoon. Marsh impoundment is discussed in detail in the Human Impacts and The Future sections of this program. There are ongoing efforts to reconnect these important habitats to the IRL. |
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This
photograph shows a small panne which is partially dried up. Although it is
located fairly high on the marsh (notice the needle rush next to it),
isolated pannes like this one are able to exchange water with the lagoon
during the highest tides of the season.
This photograph also shows several dead trees. These are black mangroves that were killed during a severe freeze in the winter of 1989-1990. Mangroves are not a natural feature of the tidal salt marsh community, but they have invaded those portions of the marsh which have been impounded for mosquito control. Mangroves are the dominant emergent (above water) wetland vegetation in the southern portion of the IRL. Salt marshes replace mangroves as the dominant wetland vegetation type in the northern part of the lagoon - dominating from Daytona Beach northward.
The salt marsh is home to a variety of animal species, including the
American alligator and the endangered Atlantic saltmarsh snake. Until
recently, the saltmarsh snake was thought to occur only within the marshes
of the IRL region. The marsh is also home to marsh rabbits, turtles and
insects, as well as threatened bird species like clapper rails. Marine
organisms within the salt marsh habitat include a variety of fishes,
crustaceans, snails, oysters and mussels.
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Information provided by: http://www.epa.gov