Associational defense against herbivory between brown seaweeds

Abstract

Pereira R.C., Bianco É.M., Bueno L.B., de Oliveira M.A.L., Pamplona O.S. and da Gama B.A.P. 2010. Associational defense against herbivory between brown seaweeds. Phycologia 49: 424–428. DOI: 10.2216/09-84.1Several associations between marine organisms have been hypothesised to be chemically mediated, but few examples have been experimentally investigated to date. In the Brazilian littoral, the presence of Dictyota species living on various species of Sargassum is a very common feature, and here we present experimental evidence that the association between the brown seaweeds Dictyota sp. and Sargassum furcatum is chemically mediated. When separated but offered simultaneously to the herbivorous sea urchin Lytechinus variegatus, S. furcatum was more highly consumed than Dictyota sp. However, when S. furcatum was tied to Dictyota sp., it was significantly less consumed by L. variegatus. Crude extracts of Dictyota sp. were significantly less consumed by L. variegatus than were extracts of S. furcatum when the extracts were offered individually or paired. Plastic mimics of Dictyota sp. did not provide protection against consumption of S. furcatum by L. variegatus, confirming that S. furcatum protection was due to Dictyota sp. chemicals. Associational defense is defined as protection gained by an organism from living in association with another species. Clearly, chemicals produced by Dictyota sp. can provide an associational refuge. Considering that Dictyota species are frequently found growing epiphytically on many benthic species, associational defenses involving Dictyota spp. may be an important aspect to the structure and dynamics of many coastal communities.