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

Because most distributional or ecologic studies of foraminifera are based more upon dead than living assemblages, it is essential to evaluate the effectiveness of current transport in dead-test distribution. Currents are negligible within Florida Bay. Gorsline (1963) measured currents within the open "lakes" of the bay, where depth and fetch are at a maximum, at < 1 cm/s, a rate insufficient to erode bottom sediment (Shinn et al., in prep.); however, Gorsline also demonstrated a counterclockwise gyral circulation pattern in several "lake" basins which he suggested would be adequate to winnow muddy sediment from the basin floor and deposit it on the peripheral mudbanks. (Lake floor sediments are grainy shell lags.) Prevailing wind direction and storm winds significantly affect water levels in Florida Bay (Enos and Perkins, 1979). Prolonged winds, such as the northeasterly winter storm winds, tend to push water and suspended sediments out of the bay through the tidal passes, where currents may reach 125 cm/s (Vaughan, 1935). Thus, winnowing and sorting play a significant role, resulting in the larger species being associated with the coarsest sediment, while the smaller are mainly confined to the finest sediment. On the platform margin, sand bars adjacent to muddy sand areas carry what is clearly a size-graded version of the nearby, more complete, muddy fauna. Illing (1950, 1952) found examples in the Bahamas of currents apparently carrying away smaller tests and thereby concentrating larger ones (and thus, those species which tend to be large). On the other hand, the most significant amount of faunal mixing, regardless of test size, probably takes place on the inclined surface between the margin and slope environments, where offshore movement of sediment during storms carries species from the platform to the sea floor.

Large-scale distribution of foraminifera, however, is probably not affected by current action, at least to the extent that distribution of the five platform interior subfaunas is altered. Two lines of evidence support this conclusion. First, regional arrangement of species does not seem to bear any relationship to size. In other words, a sequence of successively larger or smaller tests is not present across the platform, even though a gradient of water energy clearly exists. Second, common species, such as Amphistegina "lessonii" or Asterigerina carinata, which show a marked preference for reefs (Figs. 7, 8), do not appear to be significantly redistributed, even in areas in which strong currents are known to be active. Furthermore, it seems unlikely that currents could selectively reject empty tests of some benthic species while transporting tests of similar size belonging to another benthic species.