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Diagnostic Foraminiferal Assemblages of Florida Bay and Adjacent Shallow Waters: A Comparison

Barbara H. Lidz and Peter R. Rose

This article was originally published in the Bulletin of Marine Science, 44(1): 399-418, 1989


Restricted Interior Environment
Foraminiferal Distribution
Current Transport
Literature Cited

Ecologic studies of benthic foraminifera in Florida Bay indicate that (1) the bay is a specialized restricted platform interior environment; (2) its fauna is divisible into three subfaunas: nearshore, mudbank, and "lake"; (3) substrate, currents, wave intensity, and wave direction affect local distribution but do not alter regional patterns; and (4) faunal assemblages rather than individual species of foraminifera are diagnostic environmental indicators as many species range over several faunal zones. Foraminiferal biostratigraphy on a platform, whether modern or ancient, should involve determination of ecologic patterns of family distribution, similarities of test structure, ratios between faunal groups, and general trends of populations.

The purpose of this paper is to furnish foraminiferal data that distinguish Florida Bay, a subtropical lagoon, from the nearby open-circulation platform margin (i.e., a shelf lagoon) and to show the general trends in a foraminiferal population across a platform. Florida Bay occupies a shallow, wedge-shaped basin in the inner part of the south Florida shelf and provides an ideal setting for study of modern benthic foraminifera on a shallow-water carbonate platform. The geologic record, however, would show that Florida Bay or a similar shallow lagoon, by itself, would not be recognized without an adjacent open-circulation platform deposit for comparison. The paper thus is intended to provide a model for ecologic studies of similar lagoonal embayments regardless of age. Toward this end, we have identified benthic foraminiferal species, faunal morphology, and species abundance in and adjacent to Florida Bay and have interpreted and related these patterns to hydrography, physiography, and sedimentology across the south Florida platform.1 The paper concentrates on general broad distributions in morphology and frequency of taxa and assemblages as well as the ecologic relations between the various species and their varied environments. The foraminiferal nomenclature of Loeblich and Tappan (1964) is used throughout the paper.

The south Florida shallow-water carbonate platform is shown by distribution of Holocene foraminifera to consist of three major environments: upper slope, platform margin, and platform interior. The platform interior is further differentiated into open (inner reef tract or platform), restricted (Florida Bay), and brackish (Everglades) subenvironments. Because the environmental parameters controlling foraminiferal distribution across a platform change gradationally, a particular fauna must be regarded as a part of a larger population. Therefore, although the specified subject area of this volume is Florida Bay, this study maintains, as closely as possible, the integrity of the interrelations between the faunas of Florida Bay and those of the rest of the platform. In keeping with this intent, the paper addresses and compares the significant faunas and ecology of the adjacent platform margin environment and the platform interior subenvironments, as well as the subenvironments (open "lake," restricted mudbank, and brackish nearshore) differentiated within the specialized restricted platform interior environment of Florida Bay. A series of shoals and basins makes the shallow (0 - 3 m) lagoon that is Florida Bay specialized; the bay is further characterized by variable nutrient levels, low tides, and widely fluctuating physicochemical parameters (Ginsburg, 1956, 1964; Lloyd, 1964; Taft and Harbaugh, 1964; and Lapointe, 1989; Montague et al., 1989; Robblee et al. 1989; Ryan et al., 1989).

Previous Work

Three classic studies on systematic paleontology of Caribbean benthic foraminifera were conducted by d'Orbigny (1839) and Cushman (1921, 1922). Cushman made the first effort to interpret environmental and distributional significance in relation to depth, wave energy, and grass cover. Norton (1930) examined samples from 13 random localities in Florida and the West Indies and recognized four environmental zones on the basis of depth and temperature limits. Stubbs (1939) reported on the distribution of 61 species from seven sites in Biscayne Bay and noted bottom conditions, depth, and temperature. Specimens from the west coast of Florida near Ft. Myers were described by Bandy (1956), who related the faunas or "biofacies" mainly to depth. In an ecological survey of foraminifera in the northern Florida Keys, Moore (1957) reported on assemblages typical of four environments: Florida Bay, backreef, reef, and forereef. Phleger and Parker (1951) and Phleger (1960) discussed the coral reef fauna in a general ecological reference work.

In 1960 Bandy published his observations on correlation of foraminiferal structure and shape with environment. Bock et al. (1971) also addressed the morphologic relation to species with environment in a systematic/ecologic study in Florida Bay and adjacent areas; the reader is referred to this work for photomicrographs of the species discussed in the present paper. Most recently, the occurrence, frequency, and habitats of diagnostic assemblages of foraminifera from south Florida, including Florida Bay, were compared by Rose and Lidz (1977) with those of the same species found on the Bahamas carbonate platform. For a comprehensive listing of papers on tropical faunas from the Bahamas and other areas of the Caribbean, the reader is directed to Culver and Buzas (1982).

1 Editors' note: This paper is exerpted, with modifications, from an earlier publication (Rose and Lidz, 1977) of limited circulation and merits inclusion in this volume because of its significance, relevance, and because the work has not been superseded.

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