|Themes > Science > Botanical Sciences > Most Threatened Habitats > Salt Marsh Habitats|
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).
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.
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.
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.
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.
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.