Published online by Cambridge University Press: 10 March 2009
A single trophic interaction between two major biotic components within similar ecosystems can reveal high variability. In fact, in situ measurements of the trophic interactions, as provided by the field application of stable isotopes, are likely to reveal strong differences in patterns. An illustration of such a geographical plasticity is provided when regarding the trophic interaction between two major components of intertidal habitats namely, the oyster Crassostrea gigas and the microphytobenthos. The contribution of benthic diatoms to oysters' diets ranged from 4.4±3.5% in the Mont St Michel bay to 69.6±1.1% in the Marennes-Oléron bay, as estimated from δ13C and δ15N analyses. Concerning food web investigations, these results point out serious limits for extrapolating qualitative and quantitative observations related to the major trophic links between identical food sources and consumers inhabiting similar ecosystems.