Non-toxic Antifouling Activity of Polymeric 3-alkylpyridinium Salts from the Mediterranean Sponge Reniera sarai (Pulitzer-Finali) MARCO FAIMALI a , KRISTINA SEPC ˇ IC ´ b , TOM TURK b and SEBASTIANO GERACI a, * a Consiglio Nazionale delle Ricerche, Istituto per la Corrosione Marina dei Metalli, Via De Marini 6, 16149 Genova, Italy; b Department of Biology, Biotechnical Faculty, University of Ljubljana, Vec ˇna pot 111, 1000 Ljubljana, Slovenia (Received 12 March 2002; in final form 22 June 2002) The antifouling activity and toxicity of polymeric 3-alkylpyridinium salts (poly-APS) isolated from the Mediterranean sponge Reniera sarai were studied. The activity of these natural products was compared to that of zinc and copper complexes of pyrithione, two non- persistent booster biocides successfully used in current antifouling coatings. Larvae of Balanus amphitrite (cyprids and nauplii) were used to monitor settlement inhibition and the extent to which inhibition was due to toxicity. The microalga Tetraselmis suecica and larvae of the mussel Mytilus galloprovincialis were used in toxicity bioassays. Compared to the booster biocides, poly-APS were less effective at inhibiting cyprid settlement, but their effects were non toxic and reversible, with very low toxicity against the organisms used in the toxicity bioassays. Although encouraging, these results are not enough to warrant the use of poly-APS as a potential commercial antifoulant. They however justify possible future efforts to chemically synthesize poly-APS analogues for further tests. Keywords: natural products; alkylpyridinium polymers; antifouling products; bioassays; toxicity; zinc/copper pyrithione; Reniera sarai Abbreviations: Poly-APS, polymeric alkylpyridinium salts; TBT, tributyltin; NPA, natural product with antifouling activity; AF, antifouling; FNSW, filtered natural sea water; Zn-P, zinc [ pyridine-2,6- 14 C]pyrithione (Zinc Omadine w ); Cu-P, copper [ pyridine-2,6- 14 C]pyrithione (Copper Omadine w ); L:D cycle, light: dark cycle; EC 50 , the concentration of the antifouling compound causing settlement inhibition of 50% experimental organisms; IC 50 , the concentration of the antifouling compound causing inhibitory effects (swimming inhibition or inhibition of algal duplication) on 50% of experimental organisms; LC 50 , the concentration of the antifouling compound causing death of 50% of experimental organisms. INTRODUCTION Marine organisms represent a rich source of chemically novel compounds with a broad spectrum of bioactivity. Early research on such natural products extracted from marine organisms was mainly directed towards identification of com- pounds with biocidal activity for use as potential chemotherapeutic agents (Munro, 1987). However, the absence of epibionts on some benthic organisms suggested that some of these molecules could have a protective role against fouling, and this has subsequently led researchers to investigate their potential activity in both a basic and applied context. Natural products with antifouling activity (or NPAs, Clare, 1998) have been isolated from a wide range of sessile marine organisms including gorgo- nians, sponges, bryozoans, ascidians, algae and sea- grasses (for reviews see Davis et al., 1989; Holmstro ¨m and Kjelleberg, 1994; Clare, 1996). The development of coatings based on natural products from marine organisms (de Nys et al., 1995; 1996; Rittschof, 2000) is a promising alternative to the present antifouling technologies, particularly since TBT based, and possibly other metal based paints, are to be banned from the global market. The use of self-polishing coatings containing organotin compounds was banned by the European Community in December 1989. This measure was taken as a consequence of the severe environmental impacts of TBT since ISSN 0892-7014 print/ISSN 1029-2454 online q 2003 Taylor & Francis Ltd DOI: 10.1080/0892701021000036966 *Corresponding author; fax: þ39 10 647 54 00; e-mail: geraci@icmm.ge.cnr.it Biofouling, 2003 Vol 19 (1), pp 47–56