DNA damage in two bivalve species: Mytilus galloprovincialis and Ruditapes decussatus from the South coast of Portugal

Dissertação de mest., Estudos Marinhos e Costeiros, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2009

In the last years, several studies have been carried out to assess the environmental “health” of the South Coast of Portugal. The aim of the present thesis was to evaluate DNA damage as a biomarker of genotoxic contamination in two bivalve species from the south coast of Portugal, mussels Mytilus galloprovincialis and clams Ruditapes decussatus. Mussels were sampled at nine sites along the coast, and clams were collected at four shellfish beds in the Ria Formosa Lagoon. The alkaline version of the Comet assay was used to estimate the DNA damage present in the haemolymph of bivalves. An image analysis system (Komet 5.5, Kinetic Imaging Ltd) was applied and 3 parameters were calculated, Tail DNA (%), Olive Tail Moment (OTM; arbitrary units) and Tail length (μm). Data obtained for both species were low, in the same order of magnitude for sites considered as reference. These values can be used as baseline/reference levels of the genotoxic contamination for future studies made in the South coast of Portugal. The nature and magnitude of contaminants in this coast were not particularly genotoxic. DNA damage present in mussel and clams haemolymph revealed to be a sensitive biomarker of genotoxic contamination. DNA damage in both specimens responded to the existing differences between sites and seasons, with highest values during summer. This damage biomarker was also sensitive to gender differences concerning both species and the overall data indicates that females have higher DNA damage than males. Moreover, this study demonstrated that information about the condition index (and Abstract - iii - reproductive cycle) and the local abiotic conditions are essential for the appropriate explanation of data. When comparing the DNA damage between the two analysed species, collected from close sites, DNA damage was relatively similar for both bivalve species. However, while mussels had highest DNA damage in August, clams showed maximum values in February/March, suggesting some interspecific differences possibly associated with dissimilar trophic strategies and/or habitats. Lipid peroxidation (LPO) was also analysed, to verify if the environmental conditions (contaminants and abiotic factors) can induce injuries in both cellular membranes and DNA. For mussels, the compounds/factors affecting LPO can also promote (low) genotoxicity. For clams, this relationship was only verified during July. Concluding, the present thesis demonstrates that the DNA damage present in M. galloprovincialis and R. decussatus is a sensitive biomarker to discriminate spatial, temporal and genders differences, revealing to be an appropriate tool for the evaluation of genotoxic contamination along the South coast of Portugal.