Plants

Marine Grass Bed Ecosystem
The marine grass bed ecosystem grows throughout the protected seashore waters, where sandy bottoms, shell fragments and calm waters provide the proper habitat. The sea grasses occur in isolated patches usually less than several hundred acres in size. In the turbid Mississippi Sound waters, the sea grasses are rarely found in water deeper than 6 feet. These communities provide food for the marine ecosystem. In addition, they provide cover for many young fish. Although the grass beds make up only a small percentage of the total submerged lands around the Seashore islands, the fauna observed in association with them, especially the invertebrates, appears far greater than the more extensive sandy areas.

The sea grass community is very fragile and easily disturbed by human activity, such as propeller scarring and turbidity increases caused by dredging.

Storm activity, especially hurricanes, can also lead to extensive grass bed destruction. Prior to 1969, an estimated 20,000 acres of grass beds existed in the Mississippi Sound; however, much of this acreage was destroyed by hurricane Camille and the grass beds have not yet completely reestablished.

Before the passage of Camille through Mississippi Sound, three sea grass species were dominant along the Mississippi offshore islands. These species were shoal grass, manatee grass, and turtle grass. Large expanses (up to several hundred acres in size) of these sea grasses grew in conjunction with red, brown, and green algae. Due to extensive shifting sands and increased water turbulence, large expanses of sea grasses were lost during hurricane Camille, particularly around Ship Island. The grass beds along East and West Ship Island are generally found within 1,500 feet of the shoreline. Grass bed coverage along the sound side of Horn Island was also dramatically reduced by hurricane Camille. However, increased species diversity is found off Horn Island, with occasional patches of manatee and turtle grass. Petit Bois, which was the furthest from hurricane Camille, was least affected. Large expanses of diverse grass beds can still be found off the sound side shore of Petit Bois Island.

Submerged grass beds within the Davis Bayou area are restricted to small isolated bayous.

Barrier Island Ecosystem
The barrier island ecosystem is found on East Ship Island, Cat Island, Horn Island and Petit Bois Island. This ecosystem consists of four major communities: beach/dune, interdunal, upland woody, and saltmarsh.

In several of the Seashore units the interdunal area is interspersed with frequent brackish ponds. The ponds occur in depressions caused by hurricane storm surges rushing across the island and gouging out shallow indentations in the sand. The density of the widgeon grass vegetation in these ponds varies from very dense to very sparse. The pond margins are vegetated by saltmarsh grass and cattail. Cattails are usually found where there is fresh water.

Upland/Lowland Hardwood and Pine Ecosystem
The upland/lowland hardwood and pine ecosystem, a complex ecosystem composed of several vegetative communities, is located in the Davis Bayou unit. The location of these communities within the site is largely dependent on the relationship between water drainage and elevation.

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Last Updated: 1/6/03
Webmaster Gulf Islands
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