TRANSPORT AND DEFENSIVE ROLE OF ELATOL AT THE SURFACE OF THE RED SEAWEED LAURENCIA OBTUSA (CERAMIALES, RHODOPHYTA) 1 Daniela B. Sudatti Po ´ s-Graduac ¸a ˜o em Biologia Marinha, Instituto de Biologia, Universidade Federal Fluminense, PO Box 100.644, CEP 24001-970, Nitero ´i, Rio de Janeiro, Brazil Silvana V. Rodrigues Departamento de Quı ´mica Analı ´tica, Universidade Federal Fluminense, Outeiro de Sa ˜o Joa ˜o Batista, s ⁄ n, Nitero ´i, Rio de Janeiro, Brazil Ricardo Coutinho Instituto de Estudos do Mar Almirante Paulo Moreira (IEAPM)-R. Kioto, 253 CEP 28930-000 Arraial do Cabo, Rio de Janeiro, Brazil Bernardo A. P. da Gama Po ´ s-Graduac ¸a ˜o em Biologia Marinha, Instituto de Biologia, Universidade Federal Fluminense, PO Box 100.644, CEP 24001-970, Nitero ´i, Rio de Janeiro, Brazil Leonardo T. Salgado Laborato ´rio de Biomineralizac ¸a ˜o, Departamento de Histologia e Embriologia, Instituto de Cie ˆncias Biome ´dicas, Centro de Cie ˆncias da Sau ´ de, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil Gilberto M. Amado Filho Programa Zona Costeira, Instituto de Pesquisas Jardim Bota ˆnico, Ministe ´rio do Meio Ambiente, Rio de Janeiro, Brazil and Renato C. Pereira 2 Po ´ s-Graduac ¸a ˜o em Biologia Marinha, Instituto de Biologia, Universidade Federal Fluminense, PO Box 100.644, CEP 24001-970, Nitero ´i, Rio de Janeiro, Brazil Natural within-thallus concentrations of elatol pro- duced by Laurencia obtusa (Huds.) J. V. Lamour. inhibit herbivory and prevent fouling. However, ela- tol occurs in larger amounts within the thallus com- pared with the quantities from the surface of this alga. We evaluated whether the surface elatol con- centrations inhibit both herbivory and fouling and whether the content of corps en cerise can be trans- ferred to the external cell walls. Surface elatol con- centrations did not inhibit herbivory by sea urchins, settlement of barnacle larvae, or mussel attachment. Evidence of a connection between the corps en cer- ise, where elatol is probably stored, and the cell wall of L. obtusa was based on channel-like membranous connections that transport vesicles from the corps to the cell wall region. Therefore, L. obtusa presents a specific process of chemical transport between the cell storage structures and the plant surface. We hypothesized that if high amounts of elatol are capable of inhibiting herbivory and fouling, if the tested organisms are ecologically relevant, and if elatol really occurs on the surface of L. obtusa and this seaweed can transport this compound to its sur- face, the low natural concentration of defensive chemicals on the surface of L. obtusa is probably not absolute but may be variable according to envi- ronmental conditions. We also hypothesized that herbivory and fouling would not exert the same selective force for the production of defensive chemicals on L. obtusa’s surface since the low con- centrations of elatol were inefficient to inhibit either processes or distinguish selective pressures. Key index words: chemical defense; elatol; fouling; herbivory; Laurencia obtusa Abbreviation: Rf, retention factor Secondary metabolites play an important role in mediating complex ecological interactions in the sea, including predator-prey and competitive inter- actions, settlement cues, and potential defenses against infection by microorganisms (see recent review by Paul et al. 2006). For seaweeds, most evidence for the chemical mediation of ecological 1 Received 10 January 2007. Accepted 27 September 2007. 2 Author for correspondence: e-mail renato.pereira@pq.cnpq.br. J. Phycol. 44, 584–591 (2008) Ó 2008 Phycological Society of America DOI: 10.1111/j.1529-8817.2008.00507.x 584