Stable carbon and nitrogen isotope analysis of Nephrops norvegicus I Merluccius merluccius fishing grounds in the Bay of Biscay (Northeast Atlantic)

摘要

The trophic structure of the benthic ecosystem of the Grande Vasière (Great Mud Bank), a heavily trawled area in the Bay of Biscay, is largely unknown. To better understand the biotic interactions between exploited species (mainly Norway lobster, Nephrops norvegicus, and European hake, Merluccius merluccius) and their competitors and prey, we applied a dual stable carbon (~(13)C/~(12)C) and nitrogen (~(15)N/~(14)N) isotope analysis to determine trophic levels and differences in the potential food sources of species in the benthic and demersal communities. Five main groups of species constitute the basis of the trophic structure. They are distributed in three main trophic levels: primary consumers; secondary consumers including N norvegicus and juvenile M. merluccius; and top predators including adult M. merluccius (δ~(15)N = 14.5‰). The large differences in δ~(13)C values within the primary consumers attest to two différent food components: a pelagic component composed of fresh sedimenting particulate organic matter, which mainly supplies supra- and epi-benthic suspension feeders, and zooplankton, and a benthic component, which mainly supplies deposit feeders. For the predators, the target species, and their competitors, diet changes during the life-span are reflected by differences in isotope values for the size classes.