Biological succession on silicone fouling-release surfaces: long-term exposure tests in the harbour of Ischia, Italy

A static test site was set up in the Harbour of Ischia (Gulf of Naples, Italy) to investigate the antifouling effectiveness of newly developed non-polluting coatings. Two-year exposure experiments were performed on sets of panels coated with silicone-based coatings, and results were compared both to sets of panels coated with toxic agents, and non-toxic epoxydic compounds. Abiotic factors, strength of adhesion of the temporal dynamics of succession of foulers were analyzed throughout the period of immersion. Brown algae constantly represented the "border point" between the early community, dominated by slime, micro- and macroalgae, and the late community, mainly represented by bryozoans and molluscs, as well as polychaetes, sponges and tunicates. Brown algae, such as Ectocarpus siliculosus tunicates (mainly Botryllus schlosseri) and polychaetes (Hydroides elegans, Pileolaria pseudomilitaris) were demonstrated to be key species, triggering the community and influencing its development. Light was the main abiotic factor discriminating the community on the two sides of panels exposed to different irradiances. The best performing coatings (silicone easy release coatings without additives) substantially influenced community structure, shifting it to the earliest stages of colonization. Silicone coatings proved to be unsuitable for colonization by organisms typical of mature communities, due to their low energy surfaces. The results of the present paper demonstrate that silicone coatings technology represents an alternative to the use of biocidal antifouling paints