[en] Black corals are organisms characterized by a long lifespan, a very slow growth rate and late maturity. Extensive multi-specific black coral beds are encountered in the shallow-waters areas of the southwestern coast of Madagascar. These species have very diverse morphologies, from a single stem to a bushy tree shape. In addition, these black corals host very diverse symbiotic organisms. Nature of the symbiotic relationships is unknown for most of these organisms and, in particular, the nature of trophic relationship between symbiotic species and their host.
Here, we studied for the first time the isotopic composition of carbon and nitrogen of different black corals and four common symbionts. The latter were either living inside the host (the newly described myzostomid Eenymeenymyzostoma nigrocorallium) or ectosymbionts (the whip coral fish Bryaninops yongeii and the two shrimps Pontonides unciger and Periclimenes sp.). The objective was to compare diet and isotopic niche of organisms living in association with antipatharians to assess the relationships between these organisms and their hosts. Using Bayesian model approach, we found different degrees of trophic dependences between host and symbionts, showing that antipatharian-symbiont relationships are complex and varied.
