A B S T R A C TMarine biofouling historically constitutes one of the major constraints faced by mankind in its oceanic activities. The search for alternatives to TBT-based antifouling paints has led several researchers to focus efforts in the development of environmentally friendly natural compounds. This work has contributed with this search, testing the antifouling potential of crude organic extracts from four seaweed species collected at Praia Branca, Guarujá district, São Paulo, Brazil. Throughout laboratory antifouling assays in which the attachment of a common fouling organism, the brown mussel Perna perna, was employed, antifouling activity (p < 0.05) was detected in natural concentrations of the extracts of Jania rubens (Rhodophyta, Cryptonemiales) and Bryothamnion seaforthii (Rhodophyta, Ceramiales), while Dictyopteris delicatula (Phaeophyta, Dictyotales) and Heterosiphonia gibbesii (Rhodophyta, Ceramiales) did not exhibit fouling inhibition. From the algae that exhibited antifouling activity, J. rubens presented best performance when compared to that of B. seaforthii. Future field studies would be necessary to obtain results that can better reflect natural conditions, as well as to assess the activity spectrum of the antifouling activity presently recorded. Further bioassay-guided purification of the active extracts can lead to new alternatives to the metalbased antifouling paints currently in use. R E S U M OA incrustação biológica constitui, historicamente, um dos maiores problemas encontrados pelo homem em suas atividades no mar. A busca por alternativas a tintas antiincrustantes contendo tributilestanho (TBT) tem levado diversos pesquisadores a concentrar esforços no desenvolvimento de substâncias naturais menos danosas à biota marinha. Este trabalho procurou contribuir com essa busca, testando o potencial antiincrustante de quatro diferentes espécies de macroalgas da Praia Branca, município de Guarujá, SP. Através de testes antiincrustantes em laboratório utilizando a fixação de um organismo incrustante comum, o mexilhão Perna perna, foi constatado que os extratos de Jania rubens (Rhodophyta, Cryptonemiales) e Bryothamnion seaforthii (Rhodophyta, Ceramiales), à concentração natural, apresentaram atividade antiincrustante significativa (p < 0,05), enquanto Dictyopteris delicatula (Phaeophyta, Dictyotales) e Heterosiphonia gibbesii (Rhodophyta, Ceramiales) não demonstraram eficiência na inibição da fixação de bissos do molusco. Das algas que indicaram potencial atividade contra a incrustação, J. rubens apresentou melhor desempenho em relação a B. seaforthii. Futuras investigações em campo serão necessárias para a obtenção de resultados que possam refletir melhor as condições naturais, bem como avaliar o espectro de ação da atividade antiincrustante observada. A purificação guiada por bioensaios dos extratos ativos poderá levar a novas alternativas para os antiincrustantes metálicos atualmente em uso.

The production of defence metabolites is assumed to be costly in metabolic terms. If this holds true, low-light stress should reduce the ability of seaweeds to defend themselves chemically against herbivory and fouling. We investigated the eVect of energy limitation on the defensive status of seaweeds by assessing their attractiveness to mesograzers and their activity against a bivalve macrofouler in comparison with non-stressed conspeciWcs. The macroalgae Codium decorticatum (Woodw.) M. Howe, Osmundaria obtusiloba (C. Agardh) R. E. Norris, Pterocladiella capillacea (S. G. Gmel.) Santel. and Hommer., Sargassum vulgare C. Agardh and Stypopodium zonale (Lamour.) Papenf. collected at the southeastern Brazilian coast were exposed to six levels of irradiation (between 1 and 180 mol photons m ¡2 s ¡1 ) for 10-14 days. After this period, algae from all treatment levels were: (a) processed as artiWcial food and oVered to an amphipod community dominated by Elasmopus brasiliensis Dana and (b) extracted to test for diVerences in settlement rates of the fouling mussel Perna perna L. on Wlter paper loaded with the crude extracts. Generally, photosynthesis rates and growth were reduced under low light conditions. Attractiveness to herbivores and macrofoulers, however, was insensitive to energy limitation. We discuss possible explanations for the observed absence of a relationship between light availability and algal defence including the change in nutritional value of the algal tissue, the allocation of resources towards defence instead of growth and the absence of costs for defence.