Habitat Productivity: Seagrasses and Mangroves

A major seagrass die-off in western Florida Bay (Everglades National Park) is the focus of a 3-yr Coastal Ocean Program project begun in July 1990. Periodic quantitative collections of fishes, invertebrates, sediments, and plants are made in four habitats: healthy Thalassia, open water caused by die-off, and recolonizing algae (Halimeda, Penicillus) and Halodule. Sediments in die-off patches, ranging in size from square meters to hectares, are easily resuspended by winds. Sediment instability and increased susceptibility to predators are hypothesized to be controlling benthic faunal densities in die-off patches. Loss of benthic prey may be linked to decreased macrofaunal abundance in disturbed areas. In Rookery Bay, Florida, macrofaunal and infauna of intertidal mangrove, seagrass, and open water habitats were compared quarterly using quantitative samplers during high tides. Habitat-specific dominants were found, but most have been reported as abundant in other habitats elsewhere and they usually changed seasonally. Within each quarter, among-habitat differences in abundance of major taxa were not detected, except shrimps which were always significantly more numerous in seagrasses. Red mangroves were thus utilized by both resident and transient species at densities similar to those typically found in seagrasses and open waters and should be conserved as valuable habitats.