ANALYSIS OF MARINE MACROBENTHIC COMMUNITY STRUCTURE IN RELATION TO POLLUTION, NATURAL OIL SEEPAGE AND SEASONAL DISTURBANCE IN A TROPICAL ENVIRONMENT (TRINIDAD, WEST-INDIES)

Macrobenthic species abundances and biomasses were determined at 31 stations from Pointe-a-Pierre to La Brea, Trinidad. This area is subject to chronic natural oil seepage and spillage from oil production activities. Multivariate analysis was used to define those environmental variables which best explained community composition. The deeper sites were impoverished due to the development of anoxia below a pycnocline which formed during the wet season. Abundance/biomass comparison (ABC) plots indicated that macrobenthic communities near an oil refinery were grossly to moderately stressed while those close to the Trinidad Pitch Lake, one of the largest natural oil seeps in the world, were not. Taxonomic aggregation of the species data to family level resulted in little loss of information in the multivariate analyses and apparently improved the ability of ABC curves to discriminate pollution. Comparisons of the severity of community degradation at these sites using a phylum-level meta-analysis of 'production' were compatible with NE Atlantic data, which augurs well for the more global applicability of this approach. A feature of the Trinidad samples is that they all separate along the upper edge of the meta-analysis 'wedge', due mainly to their higher average proportion of Crustaced relative to Echinodermata and Mollusca. This is explained in terms of the estuarine character of the region, and suggests that the unexplained vertical axis in Warwick & Clarke's (companion article) ordination may be related to natural environmental characteristics.