Ascidians as models for the study of the effects of antifouling compounds on biodiversity in the Lagoon of Venice

Mainly contaminants with deleterious effects on the coastal marine biocoenoses have been indiscriminately introduced in the Lagoon of Venice, especially during the last fifty years from both direct and indirect poluting sorces, following the increase in the agro-industrial productiveness and the tourist and commercial harbour activities of the Venetian Region. In particular, beginning from the second half of 1960s, biocides based on organotin compounds (TPT, TBT and their derivatives) were massively introduced in the formulation of the antifouling paints used for the preservation of materials used for submerged structures as boat, hulls and helixes, buoys and moles from the settlement of various aquatic sessile organisms. These substances proved to be very harmful to the benthic marine biocoenoses, in particular to filter-feeding organisms, and, frequently, result persistent in the environment (Bryan et al., 1986; Henderson and Salazar, 1996; Hoch, 2001; Cima et al., 2002). In this study, the colonial acidian Botryllus schlosseri was used as an experimental model to evaluate the risks of new antifouling compounds, alternative to organotins through the study of their effects on larval settlement and individual survival. We studied the settlement and metamorphosis ability of larvae in the presence of either substrates coated with various paints which are usually in commerce in the Lagoon area or sea water containing various concentrations of active antifouling principles. Moreover, since alterations in the functonality of the immune system represent a great risk for the survival of individuals, we set up a series of functional assays on cultured haemocytes to be used as biomarkers for the evaluation of the immunotoxicity of these substaces. Results provide new clues to better understand the effects of the antifouling compounds on aquatic organisms and highlight the concrete risk represented by these compounds for the survival of filtering marine species and, as a consequence, for Lagoon biodiversity. (This work was supported by Co.Ri.La.)