Foraminiferal analysis was conducted on 403 bottom samples from St. Andrew Bay, a polyhaline to ultrahaline estuary on the northwest coast of Florida. Intertidal samples (140) and subtidal samples (263) were collected by the National Marine Fisheries Service during November 1974 and April 1975. Water properties samples were collected also at 69 of the subtidal stations. Foraminiferal concentrates were obtained by carbon tetrachloride float from an undisturbed, upper 1 cm (0.4 in.) of tube (intertidal) and grab (subtidal) samples. A census of populations was taken by random, 300-specimen counts. Subspecies were recognized but none are new. Biofacies were based on percentages of populations and geographic patterns of distribution.

The genus Ammonia dominates foraminiferal populations at 75% of the statistically valid stations (stations with 300 or more foraminifera) and forms the only major biofacies of the bay. Ammonia parkinsoniana tepida and typica are the dominant Ammonia. The smaller and more fragile A. parkinsoniana tepida is dominant in the central, deeper parts of the St. Andrew Bay, where salinity and temperature are higher; whereas A. parkinsoniana typica is dominant in intertidal areas, where salinity and temperature are lower. The salinity and temperature relationships of the ecophenotypes are the same as reported for San Antonio Bay, Texas, but the bathymetric relationships are reversed. The ecophenotypes define secondary biofacies within the major one.

Several species characteristic of the continental shelf occur in widely varying percentages, but with a definite geographic pattern, along the deepest and most central parts of the bay. It is suggested that this secondary biofacies reflects the effect of flood tidal action on meroplanktonic larval stages of the species.

The remaining 25% of the stations are dominated by Elphidium, miliolids, Ammobaculites, Nonionella, Miliammina, Rosalina, and Trochammina, which occur erratically in abundance and distribution. Elphidium shows the greatest adaptability to pollution. No biologic relationship is apparent between bottom sediment and foraminifers.

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