Diet and association of <i>Pontonia pinnophylax</i> occurring in <i>Pinna nobilis</i>: insights from stable isotope analysis

Stable carbon isotope measurements (δ 13 C) were used to assess the sources of carbon assimilated by the fan mussel Pinna nobilis , in sea grass Posidonia oceanica meadows, and an associated shrimp Pontonia pinnophylax which occurs within this bivalve's mantle cavity. The primary carbon sources available to both animals displayed a wide range of δ 13 C values, from −12·3 to −22·3‰. The δ 13 C and δ 15 N of Pinna nobilis and Pontonia pinnophylax suggest that they assimilate carbon from similar sources, occupy comparable trophic levels and that their association is commensal.