Twenty-eight modern bottom samples from marshes in Hancock County, Mississippi, and Pearl River, Louisiana, yielded variable foraminiferal populations (total = live plus dead) during May and June 1981. Fourteen stations were sampled twice--at "peak" high and low tides.

We identified 22 benthic species of foraminifera in the samples (counts of approximately 300 specimens/sample); no planktonic species occurred. Diversity patterns [S = number of species, H(S) = Shannon-Weiner

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information function, E = species equability among the 14 doubly sampled stations indicate that the following ranges and averages (X) exist at high tide: S = 2 to 13, X = 7.5; H(S) = 0.311 to 2.046, X = 1.25; E = 0.306 to 0.720, X = 0.522. Low-tide samples have these ranges and averages: S = 2 to 12, X = 7.0; H(S) = 1.721 to 3.750, X = 1.08; E = 0.326 to 0.727, X = 0.488. In comparison to low-tide samples, high-tide samples have a higher species diversity, slightly lower dominance, and are more equable.

Three microbiotopes occur among the 14 stations: (1) beach at 3 stations, (2) lacustrine at 3 stations, and (3) bayou-fluvial at 8 stations. Among the microbiotopes, the beach marshes have the highest diversity (S = 10), the least dominance [H(S) = 1.36], and are least equable (E = 0.400). Lacustrine environments exhibit the greatest dominance [H(S) = 0.969] and equability (E = 0.635), although the diversity is midrange (S = 6.5). The bayou-fluvial marshes show a lower diversity (S = 6.12) and have midrange values for dominance and equability (S = 1.17; E = 0.510).

In the beach and bayou-fluvial marshes, arenaceous foraminifera dominate; however, a calcareous form, Discorbis sp., dominates the lacustrine marshes. Numerical abundance (number of individuals) and the diversity of the less common species appear to cause the greatest differences between microbiotopes.

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