Positive interaction between the native macroalgae Sargassum sp. and the exotic bivalve Isognomon bicolor?

Abstract

Maria Soledad Lopez and Ricardo Coutinho Instituto de Estudos do Mar Almirante Paulo Divisao de Bioincrustacao, Departamento de Oceanografia. Moreira. (Rua Kioto 253, Praia dos Anjos, Arraial do Cabo, RJ, Brasil) Universidade Federal do Rio de Janeiro Programa de Pos-graduacao em Ecologia (Av. Brigadeiro Trompowsky, s/no. Ilha do Fundao, RJ. Brasil) Biological invasions are one of the most alarming causes of ecosystem changes (CARLTON, 1987; CROOKS, 2002) and economic losses (PIMENTEL et al., 2000). Exotic species are capable of changing the structure, organization and function of the invaded ecosystems (SHEA; CHESSON, 2002). Nowadays, researchers are especially interested in evaluating the negative impact of invaders on native communities (RUIZ et al., 1999; MILLER et al., 2002), identifying the factors that may create resistance or facilitate the introduction of exotic species. Most of the studies have focussed on negative interactions such as competition and predation (DIEDERICH, 2006; GROSHOLZ et al ., 2000); however, positive interactions between exotic and native species have recently been registered in many marine systems (CROOKS, 2002; RODRIGUEZ, 2006; RUESINK, 2007). Positive interactions potentially enhance the establishment and the range of distribution of the exotic species or increase their abundance until they become ( until they become ?) invaders. Non-indigenous species have been reported on Brazilian coasts and have become a subject of great concern (DA SILVA; SOUZA, 2004). The purse-oyster Isognomon bicolor (C.B. Adams 1845) (Bivalvia: Isognomonidae) is a bivalve originally distributed in the Caribbean region that has been identified as an exotic species on Brazilian shores, from Rio Grande do Norte to Santa Catarina states. On rocky shores in the north of Rio de Janeiro state, I. bicolor has became an important component on the mid-shore level (DOMANESCHI; MARTINS, 2002). Also, at the intertidal zone of some wave-protected rocky shores, the macroalgae Sargassum sp. forms dense beds on the fringe of the infra-littoral level, and numerous individuals of the exotic bivalve have been observed under the macroalgae fronds. These preliminary observations have suggested a positive association between the native macroalgae Sargassum sp. and the exotic bivalve. So, in this study we tested