Effects of new antifouling paints on the macrofouling biocoenosis of hard substratum in the Lagoon of Venice.

Biofouling is the natural association of sessile marine animals and plants encrusting submerged hard substrata and steady structures, the biotic composition and succession of which depends on geographic place, type of substratum, physico-chemical characteristics of the seawater and seasonal climatic conditions. In the lagoon of Venice, the climax of this biocoenosis is reached in summer-autumn and is represented by colonial ascidians of the Botryllinae family as dominant species. Macrofouling growing on artificial objects constantly immersed in the seawater causes severe economic damages, which result in continuous maintenance of the structures and high costs due to hydrodynamic loss of the boats also involving a sensitive increase in fuel consumption and atmospheric pollution. Therefore, the study of antifouling compounds from 1970s with the introduction of organotin compounds as principal biocides is fundamental for the future of naval engineering with which it parallelly evolved. However, the severe disadvantages for environmental impact of organotins involved a strict international regulation of their employment with the purpose of reaching their total elimination within 2008. As a consequence, from 1990s, the research of alternative biocides, to be applied as antifoulings in paints for covering immersed objects, remarkably increased aiming to produce new chemical formulations effective on the biofouling and also compatible with the preservation of marine ecosystem. The purpose of our research was to evaluate the effects of some new antifouling paints in commerce, containing Cu2O, CuSCN, Sea-Nine 211, Diuron, TCMS pyridine, Zinc pyrithione, Zineb and Endosulfan as principal or booster biocides, on the ecological succession of hard substratum macrofouling employing wooden and steel panels immersed for one year in two stations of the southern Venice lagoon, different for bathymetric and hydrodynamic characteristics. Some biodiversity indexes (species richness, biocoenosis structure, covering-abundance index, similarity index) were used to describe the evolution of biocoenosis. Results, compared with control and TBT-treated panels, enabled us to highlight the disturbing activity of the antifouling paints, that results in the selection of resistant and dominant species, often different to those of the natural climax. We have established an order of biocidal efficacy of the assayed antifouling paints: TCMS pyridine, Diuron, Irgarol 1051 < Cu2O, CuSCN, Zn pyrithione, Zineb, Endosulfan, Sea-Nine 211 < TBT. None of the paints assayed is more powerful than that containing TBT and the biocidal efficacy depends on the type of matrix (hard or self-polishing) and the presence of biocidal boosters able to enlarge the toxic effect. In consideration that the wide use of these antifouling paints is accompanied by a continuous leaching of their active substances in the environment, our data evidence the dangerousness of these xenobiotics towards the coastal marine biocoenoses, in particular to fragile ecosystems like the lagoon of Venice and suggest the necessity of a revival of a more careful toxicological study of the paints already in commerce and a research of new antifouling systems which don't use chemical biocides. This work was supported by Co.Ri.La.