Abstract

Foraminifera were collected from three transects across a microtidal creek in the Caroni Swamp, northwest Trinidad (10°35′N, 61°30′W). Two transects (C1A and C1B) were taken beside a skeleton jetty, the third (C2) from the opposite bank. The heights of the 75-ml samples ranged from 0.44 m above annual mean sea level (AMSL) to 0.99 m below. Only 72% of 39 samples yielded ≥50 foraminifera, and further statistical analyses [diversity measurements, Q-mode cluster analysis, SHE Community Structure Identification (SHECSI)] were limited to these. The low abundance of foraminifera along Transect C2 might be due to erosion opposite the jetty.

Cluster analysis revealed three zones. Zone I, above 0.22 m above annual mean sea level (AMSL), is co-dominated by Arenoparrella mexicana and Trochammina inflata. Species richness (S) here is 4–10 species per sample, the information function (H’) is 0.88–1.54 and the equitability index (E) is 0.34–0.71. Zone II (~0.21 m above to ~0.45 m below AMSL) is co-dominated by Ammotium salsum, Miliammina fusca and Trochammina advena. Species richness (S) in Zone II is 7–12, H’ is 1.32–1.95 and E is 0.44–0.70. Zone III (below −0.49 m relative to AMSL) is dominated by Ammonia sp., with lesser amounts of T. advena. In this Zone, S = 4–10, H’ = 0.36–1.03 and E = 0.20–0.40. Mean values of H’ and E are highest in Zone II. Within Zones I and II, S and H’ are both negatively correlated with altitude, showing promise as proxies for altitude within these zones.

SHECSI indicated that the faunas in Zones I and III have logarithmic series population structures. However, the cumulative value of the lnE increased part way through Zone II, suggesting that this zone comprises several subzones not revealed by cluster analysis. The population in the five samples above the increase in the lnE had a logarithmic series population structure. SHE analysis reveals two further subzones below this, but the number of samples was too few for SHECSI.

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