Effects of oil pollution on aquatic macroinvertebrate assemblages in Gabon wetlands

Abstract

Macroinvertebrate assemblages from uncontaminated and contaminated sites in the Gamba Complex (Gabon) were compared, the latter sites having been subjected to ongoing oil spills since the 1970s. Vegetation communities surrounding the sites included savannah, shrub–scrub, palm forest, gallery forest and thick jungle. Aquatic macroinvertebrate diversity was high, but abundances at individual sites were low. No living aquatic macroinvertebrates were found at sites with severe oil deposits, but they were present within a few metres of these sites and their abundance increased as the amount of oil present decreased, within a few metres of such sites. Abundance and taxonomic richness declined with increasing oil levels, suggesting that oil negatively affected macroinvertebrate assemblages. Based on preliminary observations, other significant factors that influenced biodiversity were pH, water permanence, terrestrial vegetation type, and canopy cover. Further sampling of contaminated and clean sites in the region will be crucial in determining the natural biodiversity of wetland habitats such that the restoration success of these areas can be more rigorously evaluated.

Keywords: biodiversity; biomonitoring; tropics; petroleum spills; West Africa

African Journal of Aquatic Science 2008, 33(3): 261–268