Trophic resources of the bivalve, Venus verrucosa, in the Chausey archipelago (Normandy, France) determined by stable isotopes and fatty acids

Abstract : In the Chausey archipelago, growth of the burrowing bivalve Venus verrucosa (Mollusca: Veneridae) has been shown to be highly variable between closely located sites (<1 km). To explain this small-scale spatial variability, we tested the trophic hypothesis using both fatty acid markers, and carbon and nitrogen stable isotopes (delta C-13 and delta N-15). Environmental parameters, including substrate, were also analysed to discriminate their effects on potential trophic differences. Results of isotopic fractionation and lipid profiles of water column and digestive gland samples both showed a large contribution of phytoplankton to the diet of V verrucosa. More surprisingly, the same results suggest that Phaeophyceae and Rhodophyceae macroalgae could contribute to the nutrition of V verrucosa as dissolved exudates. Whereas site differences were not observed between the food sources of V verrucosa, we showed that growth performance index was correlated to wave height. Thus, we hypothesized that the high local growth variability could be controlled by the hydrosedimentary dynamics. In addition, although no significant growth differences were found between intertidal and subtidal populations, better condition index and more total lipids were found in the digestive gland of intertidal V verrucosa, suggesting potential compensatory growth mechanisms.