Individual and combined effects of cadmium and diesel on a nematode community in a laboratory microcosm experiment

A microcosm experiment was carried out to study the influence of cadmium and diesel, individually and in a mixture, on a free living nematode community of a Tunisian lagoon. Sediments were contaminated with cadmium that ranged in concentration from 0.54 to 1.40 mg Cd kg−1 (dry weight (dw)), by diesel at 0.25 mg kg−1 (dw), by a cadmium-diesel mixture (Cd at 1.40 mg kg−1+Diesel at 0.25 mg kg−1) and effects were examined after 90 days. Univariate analysis showed that all univariate indices did not change significantly neither at all the levels of cadmium contamination nor at 0.25 mg kg−1 (dw) diesel concentration. But, at the cadmium-diesel mixture, significant differences were recorded between nematode assemblages from uncontaminated sediment control microcosm and those from cadmium-diesel mixture amended sediment treatments. Total nematode abundance (I), mean individual weight (bi), Shannon-Weaver index H′, species richness (d), evenness (J′) and number of species (S) decreased significantly in microcosms contaminated with both cadmium and diesel. Results from multivariate analyses of the species abundance data demonstrated that responses of nematode species to the cadmium-diesel treatments were varied: Marylynnia stekhoveni, Calomicrolaimus honestus and Oncholaimellus mediterraneus were significantly affected at the cadmium-diesel contamination but they were not eliminated. These species could be categorized as “cadmium-diesel sensitive”. Enoploides sp. and Oncholaimus campylocercoides, characterized by increased abundances in cadmium-diesel amended sediment, seemed to be “cadmium-diesel resistant” species. All these species, “cadmium-diesel sensitive” or “cadmium-diesel resistant”, were not affected by either cadmium or diesel alone.