Nancy Gladson Diersing

Nancy Gladson Diersing: member of the Research Staff at the Florida D.E.P. Florida Marine Research Institute in Marathon, FL. Her background includes ten years as a classroom and field educator. With a master's degree in zoology, she has been very active in Florida Bay studies, and in her four years with FMRI worked on the Florida Bay Project.

Most of the basins of the Central and Western zones are less than 6 feet deep and are covered with seagrass beds of varying densities. Turtle, manatee, shoal, and widgeon grass are the common names for the four species which are found in the bay, but turtle grass is by far the most common. Basins are separated from one another by a series of grassy mudbanks. Well-established seagrass communities serve an important ecological function because they not only stabilize bottom sediments, but shelter hundreds of shrimp, crab, and fish species. Crustaceans and small fish hide between the grass blades and a host of clams, snails, and marine worms burrow in the layer of sediment which is trapped beneath the root/rhizome system of the plants. Exposed at low tide, the flats surrounding the basins are important feeding grounds for great white herons, egrets, ibis, and other birds which reside year-round or spend the winter in the bay. Southern stingrays and small bonnethead sharks may be seen rippling the surface as they cruise these shoals in search of prey. Horseshoe crabs, spider crabs, and tulip snails are conspicuous inhabitants of the grassbeds, along with various species of juvenile fish which hide amongst the blades. Shallow cuts in the banks allow for limited flow between basins. Loggerhead turtles, large bull sharks, and bottle-nosed dolphins use these channels as feeding grounds and passageways between adjacent basins.

The numerous mangrove islands scattered throughout Florida Bay formed many years ago when mangrove seedlings floating in the water colonized the shallowest portions of the system of mudflats which covers the bay bottom. The sediments and decaying plant material trapped by the sprawling roots of red mangrove trees accumulated over time creating this system of mangrove islands. During unusually high tides or storm events, most islands, which are barely above sea-level, are washed over by bay waters. The branching prop roots of the red mangroves extend from the fringe of the island into the surrounding water. Here the roots provide shelter for snook, grunt, spiny lobsters, and act as a substrate for filter-feedering sponges and feather duster worms. The interior of many islands contains an open water salt pond called a salina. Usually, the salina is surrounded by the more salt-tolerant black mangroves with their characterisitic breathing roots protruding up from the muddy, anaerobic soil. Because these islands with their dense mangrove stands are important roosting and nesting grounds for egrets, herons, eagles, ospreys, roseate spoonbills, frigates, pelicans, and cormorants. Everglades National Park has closed most of these islands to the public.