[en] Analyses of the natural abundance of carbon and nitrogen stable isotopes were performed to investigate the feeding habits of two ophiurolds, Ophiomastix venosa and Ophiocoma scolopendrina, and to assess the potential benefit obtained by the symbiotic Ophiomastix venosa juveniles. A tracer experiment was also carried Out to clarify the contribution of algae to the nitrogen uptake amongst the tested ophiurolds. Our results suggest that Ophiocoma scolopendrina adults occupy a higher position in the food web than Ophiomastix venosa and mainly feed on neuston. In contrast, O. venosa adults feed on the alga Sargassum densifolium, and on organic matter associated with sediment. Free juveniles and symbiotic juveniles of O. venosa have intermediate PC values between both adult species. The high proportion of C-13 in the symbiotic juveniles compared to the one in their conspecific adults indicates that their diet slightly differs from the latter and is closer to that of Ophiocoma scolopendrina. This raises the hypothesis that symbiotic juveniles steal neuston front their associated host, O. scolopendrina.
Centre Interfacultaire de Recherches en Océanologie - MARE
Fonds de la Recherche Scientifique (Communauté française de Belgique) - F.R.S.-FNRS
Etudes des relations symbiotiques chez les échinodermes en milieux tropicaux coralliens (Tuléar, Madagascar) (Prof I. Eekhaut)