The coralligenous ecosystem is one of the biodiversity hotspots in the Mediterranean Sea. This study aims at determining (i) the organic matter (OM) sources at the base of the food web in a coralligenous  ecosystem  near  Marseille  (Cap  Caveau,  Frioul  Island)  and  (ii)  the  global functional structure of its community. For that purpose, C and N stable isotope analyses were performed on 78 compartments or species collected in this habitat between 30 and 40 m depth.

Results  suggested  that  the  pelagic  particulate  organic  matter  (POM),  mainly  composed  of phytoplankton, was the main OM source fuelling coralligenous food webs, followed by sedimented organic matter (SOM) and some macrophytes. At least three level of consumers were identified from plankton-feeding invertebrates to piscivorous teleosts. Coralligenous food webs seemed to be characterized by a high abundance and trophic diversity of plankton and filter feeders. Among them numerous sessile invertebrates, such as cnidarians, bryozoans and ascidians, were poorly directly consumed, but played an important role in POM transfer. Further studies on spatial and temporal variations of coralligenous communities would be necessary for providing a general trophic functioning model of this highly diversified ecosystem.