Individual and combined effects of lead and zinc on a free-living marine nematode community: Results from microcosm experiments

A microcosm experiment was carried out to study the influence of lead and zinc, individually and in mixtures, on a free-living nematode community of a Tunisian lagoon. Three levels (low, medium and high) of each heavy metal were used, separately and in combinations, for sediment contamination and effects were examined after two months. Results from the multiple comparison tests showed significant differences between nematode assemblages from undisturbed controls and those from lead and/or zinc treatments. Most univariate measures, including diversity and species richness, decreased significantly in the treated microcosms. Results from multivariate analyses of the species abundance data revealed significant effects of both metals, separately or in mixtures, at all the doses tested on nematode assemblages. All treatments were significantly different from the control and from each other. Both univariate and multivariate analyses of the data showed that the differential response occurred in all treatments but the communities from microcosms contaminated with lead and zinc separately were much more strongly affected. This result is suggestive of antagonistic interactions between Pb and Zn. The responses of nematode species to the lead and zinc treatments were varied: Calomicrolaimus honestus was eliminated at all lead doses tested and seemed to be intolerant species to Pb contamination whereas Oncholaimus campylocercoides increased significantly at low and medium lead contamination, was eliminated in Pb-highly amended sediment treatments and increased at all zinc doses used. This species could be categorized as "opportunistic" at low and medium lead doses and "zinc-resistant" species. Hypodontolaimus colesi was eliminated in all replicates treated with Zn even at low concentration and appeared to be a very sensitive species to zinc contamination. (c) 2007 Elsevier B.V. All rights reserved.