No abstract

Antifouling chemical defense is likely an evolutionary response to the ecological disadvantages of epibiosis, particularly for photosynthetic organisms. Seaweed natural products with antifouling activity can provide effective, environmentally friendly alternatives to currently used antifouling paint booster biocides. The aim of this work was to assess the antifouling potential of natural products from Brazilian littoral seaweeds. Crude organic extracts from 51 populations comprising 42 species of macroalgae from eight locations along the Brazilian coast were tested against a relevant fouling organism in laboratory bioassays, the brown mussel Perna perna. In five cases, antifouling activities of purified compounds were also tested. A total of nine macroalgae were also cultured and tested for the presence of inducible defenses against fouling. Ecologically relevant field tests were performed in 11 cases to confirm laboratory results. Despite the unbalanced number of macroalgae tested among different localities, there seems to be no latitudinal trend of increased antifouling activity towards lower latitudes, where fouling pressure is presumed to be higher. However, there was a clear phylogenetic pattern in antifouling activity, with red macroalgae having the highest proportion (55%) of active species (moderate or strong fouling inhibition), followed by brown macroalgae (14%). Green seaweeds never exhibited strong antifouling activity (≥80% inhibition of byssal attachment relative to controls). Some degree of induced antifouling defense was observed in seven species (78%). These results appear to support known trends of secondary metabolite production among seaweeds and suggest that research efforts should be focused on tropical red macroalgae in the quest for new antifoulants. On the other hand, it seems clear that macroalgal groups, such as green algae, must have mechanisms of defenses against fouling that are not chemical.

The crude organic extracts of the endemic gorgonian Phyllogorgia dilatata and two sponge species Aplysina fulva and Mycale microsigmatosa were evaluated for anti-fouling properties through field experiments. To investigate this property in ecologically meaningful conditions, crude extracts from these invertebrates were incorporated at concentrations naturally found in these marine organisms into a stable gel used as a substratum for fouling settlement. Crude extract from A. fulva showed no significant anti-fouling property at the natural concentrations used in the field experiments. In fact, fouling organisms settled significantly more on gels treated with A. fulva extract than on the control gel. On the other hand, both M. microsigmatosa and P. dilatata yielded crude extracts that exhibited a selective action inhibiting only the settlement of barnacles. The evidences obtained here by means of field experiments can provide a basis for future development of one kind of natural antifoulant technology to prevent marine biofouling.Key words: marine invertebrates, anti-fouling, secondary metabolites. RESUMO Avaliação experimental de metabólitos secundários de invertebrados marinhos como antiincrustantes em campoAs propriedades antiincrustantes dos extratos brutos da gorgônia endêmica Phyllogorgia dilatata e de duas espécies de esponja, Aplysina fulva e Mycale microsigmatosa, foram avaliadas por intermédio de ensaios de campo. Para investigar essas propriedades sob condições ecologicamente relevantes, as concentrações naturais dos extratos brutos encontrados nesses invertebrados foram incorporadas a um gel estável que serviu de substrato para o assentamento de organismos incrustantes. O extrato bruto de A. fulva não mostrou efeito antiincrustante na concentração natural usada nos experimentos. De fato, os organismos incrustantes colonizaram significativamente mais o gel contendo extrato de A. fulva do que o gel-controle. Por outro lado, ambos os invertebrados, M. microsigmatosa e P. dilatata, produzem extratos brutos que foram seletivamente ativos contra o estabelecimento de balanídeos. As evidências obtidas aqui, por meio de experimentos em campo, podem ser importantes subsídios para futuras investigações visando à aplicação industrial de produtos naturais antiincrustantes em tecnologias de prevenção da bioincrustação marinha.Palavras-chave: invertebrados marinhos, antiincrustação, metabólitos secundários.