Analysis of marine macrobenthic community structure in relation to pollution, natural oil seepage and seasonal disturbance in a tropical environment (Trinidad, West Indies)

Abstract

Macrobenthic species abundances and blomasses were determined at 31 statlons from Pointe-a-Plerre to La Brea, Trinldad. Thls area is subject to chronic natural 011 seepage and spillage from oil production activities. Multivariate analysis was used to define those environmental variables which best explained community composition. The deeper sltes 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 communltles near an oil refinery were grossly to moderately stressed while those close to the Trinidad Pltch 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 multlvarlate 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 Atlantlc data, which augurs well for the more global applicability of this approach. A feature of the Tnnidad samples is that they all separate along the upper edge of the meta-analys~s 'wedge', due malnly to their higher average proportion of Crustacea relative to Echlnodermata and Mollusca. This IS explained In terms of the estuarine character of the reglon, and suggests that the unexplained vertlcal axis in Warwick & Clarke's (companion article) ordination may be related to natural environmental characteristics O Inter-Research 1993