The U.S. Geological Survey Ecosystem History of Florida Bay and the Southwest Coast Project has completed analyses of the faunal and floral record in short sediment cores from three sites in the central portion of Florida Bay. These analyses were undertaken to determine the biological, physical, and chemical parameters of the ecosystem prior to significant human impact on the south Florida region, and to determine the natural versus human-induced changes that have occurred within the ecosystem. Molluscs, benthic foraminifera, pollen, and dinocysts have been examined at 2 cm intervals in cores from the Bob Allen mudbank (core 6A), from Russell Bank (cores 19B and 19A), and from the mouth of Taylor Creek in Little Madeira Bay (core T24). Lead-210 analysis provides the age model for the cores. Analyses of ostracodes and diatoms have not been completed, and geochemical analysis of the ostracode and mollusc tests are currently being conducted. Data collected on the distributions and habitat preferences of the fauna and flora at 20 monitoring sites within Florida Bay provide the proxy data for interpreting down-core environmental conditions (Brewster-Wingard and others, 1996).

The initial emphasis of the analyses was to determine the salinity history of north-central Florida Bay, as recorded at the core sites. The benthic faunal data from Bob Allen core 6A indicate that the 1800's were a time of fluctuating, but relatively low, average salinity (Brewster-Wingard and others, 1995). In the early 1900's, a significant increase in the average salinity occurred at Bob Allen mudbank. Russell Bank core 19B also records an increase in salinity through the 1900's; polyhaline and euhaline benthic fauna increase up-core and the number of mesohaline species decreases. Taylor Creek core T24 indicates an increase in polyhaline to euhaline benthic fauna up-core (Ishman and others, 1996). The lower portion of core T24 is dominated by oligohaline to mesohaline species.

In addition to salinity history, patterns of substrate change, as indicated by the benthic fauna, have been examined. Bob Allen core 6A and Russell Bank core 19B show very similar patterns of substrate change, although at different time periods. The lower portions of both cores show a mixture of sediment dwelling and grass dwelling molluscs, whereas the upper portions are dominated by grass and/or algae dwelling molluscs. Additional data from our monitoring sites should allow us to further refine the substrate history at the individual sites.

The flora present in the cores provide links between the benthic and pelagic systems within Florida Bay and between the terrestrial and marine systems in south Florida. The pollen present in the cores link changes in the terrestrial ecosystem to changes occurring within the marine environment, allowing the determination of factors that might be affecting the entire south Florida ecosystem. In Bob Allen core 6A the pollen and dinocyst assemblages changed at approximately the same point in the core that the benthic fauna showed significant change; this implies consequential events occurred around the turn of the century that induced change in the entire south Florida ecosystem. Floral assemblages within Taylor Creek core T24 also are consistent with benthic faunal data, indicating increasing salinity up-core. Additional analyses of the distribution of dinocysts and diatoms within the cores may provide information on planktonic blooms, current patterns, and nutrient supply.

During the next year we will complete our analyses of replicate cores from Bob Allen and Russell Banks in order to address questions of reproducibility within sites. In addition, we will examine a core from Pass Key and possibly Whipray Basin to determine if the patterns of salinity and substrate change are repeated at other sites. Geochemical analyses of ostracode and mollusc shells will provide additional data on salinity and nutrients within Florida Bay. The results obtained from the analyses of cores collected in Florida Bay will be compared to similar data from the Biscayne Bay and the Southeast Coast Ecosystem History Project, from the Terrestrial Everglades Ecosystem History Project, and from the Buttonwood Embankment Project, to determine if corresponding changes occurred and, if so, can these changes be linked to human activity, to natural events, or to a combination of factors.

REFERENCES

Wingard, G.L., Ishman, S.E., Cronin, T.M., Edwards, L.E. Willard, D.A., and Halley, R.B., 1995, Preliminary analysis of down-core biotic assemblages: Bob Allen Keys, Everglades National Park, Florida Bay: U.S. Geological Survey Open-File Report 95-628, 35 p.

Ishman, S.E., Brewster-Wingard, G.L., Willard, D.A., Cronin, T.M., Edwards, L.E., and Holmes, C.W., 1996, Preliminary paleontologic report on Core T-24, Little Madeira Bay, Florida: U.S. Geological Survey Open-File Report 96-543, 27 p.

Brewster-Wingard, G.L., Ishman, S.E., Edwards, L.E., and Willard, D.A., 1996, Preliminary report on the distribution of modern fauna and flora at selected sites in north-central and north-eastern Florida Bay: U.S. Geological Survey Open-File Report 96-732, 34 p.

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