FORAMINIFERA IN THE MANGAL AT THE CARONI SWAMP, TRINIDAD: DIVERSITY, POPULATION STRUCTURE AND RELATION TO SEA LEVEL

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 ln E 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 ln E had a logarithmic series population structure. SHE analysis reveals two further subzones below this, but the number of samples was too few for SHECSI.