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
(δ13C and δ15N). 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.