Studies on macrofouling biocoenosis of hard substrates for the estimation of the environmental quality in the Lagoon of Venice.

The study of the development of macrofouling biocoenoses is of particular interest because it might represent an instrument for the evaluation of the biodiversity. In the lagoon of Venice, these studies acquire a critic relevance owing to they allow to reveal, in the long term, quality and quantity changes of the fouling community attributable to environmental differences and improve the comprehension of the existing interactions between the organisms of the fouling and some physical-chemical factors of seawater and/or xenobiotics. We carried out an analysis of the temporal sequence of the macrofouling biocoenosis of hard substrates in the southern basin of the lagoon of Venice on steel and wood panels, with the aim of developing an environmental quality index (bioindex) which was cheap, easy to calculate, sensitive to many environmental conditions and considering the relationships between the biotic data and change of highly significant chemical-physical parameters as regards the lagoon environment. It is specific for the community of hard substrates, and represented by the following algorithm: Log10 ( R • A • IpH • IT • IS ) where R = species richness, i.e., number of species by month present onto all panels of the same type; A = area extension for each species by months (cm2); IpH = pH quality index; IT = temperature quality index; IS = salinity quality index. The development of a quality index in logarithmic scale, from 1 to 10 inclusive, allows to really evaluate the state of health of the lagoon environment assigning to it a numerical value. Moreover, we investigated the disturbing action on “Botryllus biocoenosis”, a benthic association of various ascidians where the colonial species are dominant, by eight antifouling paints of new generation containing Cu2O, CuO, CuSCN, Sea-Nine 211, Irgarol 1051, Diuron, Chlorothalonil, Dichlofluanid, Zinc pyrithione, Zineb and Endosulfan as principal or booster biocides. Experiments were carried out on wood and steel panels immersed for one year in two stations of the southern basin, differing in bathymetric, hydrodynamic and turbidity characteristics. The growth and development of biocoenoses were analysed monthly and compared with both control and TBT-treated panels. Biodiversity indexes – species richness, biocoenosis structure, Benninghoff’s covering-abundance index, and Sørensen’s similarity index – were used to describe the evolution of the biocoenosis and compare the disturbing effects resulting in the selection of resistant species, often different from those of the natural relative climax. Results indicate that none of the assayed paints is more powerful than TBT-containing paints and the effects on the biocoenosis are potentiated by the type of matrix and presence of booster compounds, following the order of biocidal efficacy of paints containing TBT > organozinc > copper > Sea-Nine.