Evaluation of biomarker responses in bivalves from the Venice Lagoon: seasonal study and transplantation experiment

The present study was carried out in the lagoon of Venice to evaluate the biological responses of mussel, Mytilus galloprovincialis, and clam, Tapes philippinarum, to stress factors, both natural and anthropogenic, and to assess the effects due to spatial and temporal variations. M. galloprovincialis were seasonally sampled (2001-2002) in areas of the lagoon of Venice affected by different kinds and degree of pollution. T. philippinarum was transplanted from a reference site outside the lagoon to two different areas inside the lagoon. The biological response was evaluated at biochemical (aldehyde dehydrogenase and catalase activities), cellular (neutral red retention time), physiological (survival in air and condition index) and behavioural (reburrowing rate) levels. Mussel responses varied among the different site, mainly in relation with temperature. The difference between reference and polluted stations was clearly distinguishable only in spring and summer, underlining the heavy influence of natural factors such as temperature, food availability and the reproductive cycle on the biological response of mussels in the lagoon of Venice. Biochemical biomarkers and condition index showed spring values mostly far apart between polluted and reference samples, indicating a lesser influence, at least in this season, by natural and endogenous factors. As for survival in air, a marked difference was observed only during winter time, whereas the values of neutral red retention time ranged similarly in all seasons. The results of the transplantation experiment showed different although not significant biological responses in the clams deployed in the two lagoon sites.