Abstract Methods Restricted Interior Environment Foraminiferal Distribution Current Transport Conclusions Acknowledgments Literature Cited Appendix

Four principal interrelated ecologic factors produce variations in environment on the Florida platform: circulation of marine waters driven by the tides and winds, the most important environmental index to foraminiferal distribution on shallow-water platforms; physiography, primarily depth and configuration of local mudbank relief; high evaporation and low rainfall; and high rainfall and freshwater runoff. In Florida Bay, an area of 1,550 km² (600 mi²; Scholl, 1966, table 1), where the volume of water is small and there is only limited access to open marine water, distribution of foraminiferal faunas is controlled primarily by temperature and salinity and secondarily by wave and current action (Bock, 1971). The major physiographic-hydrographic environments, each with its typical fauna, reflect broad variations in these factors.

The restricted interior environment requires a barrier (for instance, a land mass, a submerged sill or prominence, or simply a broad expanse of shoal water) separating it from influences of normal oceanic water. Florida Bay is dominated by a series of shallow (<0.6 m) mudbanks and islands which divide the bay into slightly deeper (2 m) basins or "lakes" (Fig. 1). Stockman et al. (1967) have estimated that basins occupy 90% of the area in northeastern Florida Bay (north of lat. 25^oN and east of long. 80^o43'W) and are floored by an average of 0.15 m of coarse Holocene sediments. Banks and islands occupy 10% of this area and average 1 m of sediment. In western Florida Bay (north of lat. 24^o55'N, west of long. 80^o50'W), mudbanks become progressively wider, islands become fewer, and associated basins are poorly defined and generally contain less sediment. Narrow, well-defined, active channels interconnect most of the mudbanks of the eastern bay, whereas the western bay basins are connected by only a few sluggish, poorly defined channels in the broad banks (Enos and Perkins, 1979). Bay sediments are predominantly lime muds, with a distinct peloidal texture and varying, but subordinate, admixtures of mollusc shells and foraminifera.

Circulation of open-oceanic water into Florida Bay is restricted by the rocky Florida Keys and the broad mudbanks of western Florida Bay; circulation within the bay is further restricted by the many mudbanks. Thus, depending upon seasonal variations in rainfall and net evaporation within the bay and in the amount of mainland runoff, salinities in the bay range from 6 to 70, the highest fluctuations being in the most isolated northeastern part of the bay (Ginsburg, 1956; McCallum and Stockman, 1961; Gorsline, 1963; Lloyd, 1964; Scholl, 1966; Robblee et al., 1989). Even greater extremes occur in waters ponded on the islands. In most of the bay, however, salinity is between 35 and 40 (Enos and Perkins, 1979). Thus, either hypersaline or brackish conditions exist in Florida Bay but, because rainfall fluctuations appear to be on a 5- to 7-year climatic cycle, the bay is termed one of highly variable salinity rather than a hypersaline or brackish-water bay (Lloyd, 1964). Water temperature also varies seasonally, from 15^oC to 38^oC (Ginsburg, 1964), and with it and the salinity, water chemistry, nutrient balance, and abundance of micro-organisms change accordingly (Lapointe, 1989; Montague et al., 1989; Ryan et al., 1989).