Crude extracts of the brown seaweed Dictyota mertensii (Martius) Kützing collected at two distant and different places on the Brazilian coast, Búzios (Rio de Janeiro) and Fernando de Noronha (PE), were evaluated for defensive chemistry against the crab Pachygrapsus transversus, and the sea urchin Lytechinus variegatus. The extract from Búzios specimens of D. mertensii significantly inhibited the consumption by both P. transversus and L. varigetaus. Fractionation of the extracts of specimens of D. mertensii from Búzios and F. de Noronha followed by complementary assays revealed one active fraction from each location, which contained distinct defensive secondary metabolites. In each active fractions prenylated guaiane diterpenes were the major compounds. Dictyol H and epoxypachydictyol A were the most abundant compounds in Búzios and F. de Noronha, respectively, followed by minor components. Our results show a differential production of secondary metabolites in the two distant and different populations of D. mertensii along the Brazilian coast. This suggests that defensive chemicals from this seaweed are not qualitatively absolute characteristics of the species, but may represent an ecological specialization to successfully prevent herbivory.
Diterpenes; Dictyota mertensii; Feeding; Chemical defense variation