Salt marshes are tide-stressed environments where ecologic variables exert strong selective control upon the distribution, type, and abundance of organisms. Ecologic conditions range from marine to terrestrial; hence gradational and/or abrupt environmental changes across marshes produce similar gradients in communities of organisms and their biotopes. Salt marshes are one of the present-day sites of peat accumulation. They represent a potential milieu for lignite and coal formation. Recognition of microenvironments within such marshes will provide coal explorationists and paleontologists with another tool for predicting the location of subsurface peats, lignites, and coals.

Twenty-eight modern bottom samples were collected for analysis for foraminiferal populations (total = live + dead) in the Hancock County, Mississippi, and Pearl River, Louisiana, marshes during May and June 1981. Fourteen stations of the 28 were sampled twice--once at "peak" high tide and once at "peak" low tide. Three microbiotopes occur among the 14 stations: (1) beach (B)--3 localities, (2) lacustrine (L)--3 localities, and (3) bayou-fluvial (BF)--8 stations. Average salinities (parts/mil) at these biotopes were 10.4 (B), 2.3 (L), and 7.7 (BF). Ranges were 0.2 to 13.5. Average dissolved oxygen (ppm) values were 10.4 (B), 7.9 (L), and 5.4 (BF). Ranges were 2.6 to 12. Temperatures (°C) averaged 29.4 (B), 30.4 (L), and 29.3 (BF). Ranges were 20.9 to 32.7. We are currently studyin interbiotope and intrabiotope variability.

After extracting a minimum of 300 specimens/sample, foraminiferal species diversity patterns among the 14 doubly sampled stations were studied. We used S (number of species), H(S) (Shannon-Wiener information function), and E (species equitability). The following ranges and average (x) exist at high tide: S--2 to 13, x = 7.4; 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. High-tide samples have much higher species diversity, slightly lower dominance, and are more equable.

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