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

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Abstract:

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 (13C/12C) and nitrogen (15N/14N) 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 (15N = 14.5‰). The large differences in 13C values within the primary consumers attest to two different 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.

La structure trophique de l'écosystème benthique de la Grande Vasière, une importante zone de pêche au chalut de fond du Golfe de Gascogne, demeure encore méconnue. Afin de mieux comprendre les interactions biotiques entre les espèces exploitées (principalement la langoustine, Nephrops norvegicus, et le merlu, Merluccius merluccius) et leurs concurrents et proies, une analyse des isotopes sables du carbone (13C/12C) et de l'azote (15N/14N) a été réalisée pour étudier les différents niveaux trophiques et mettre en évidence l'existence de différentes sources de nourriture potentielles des communautés benthiques et démersales. Cinq principaux groupes trophiques constituent la base de la structure de la chaîne alimentaire. Trois niveaux trophiques ont été identifiés : consommateurs primaires, consommateurs secondaires (N. norvegicus et les juvéniles de M. merluccius) et les supers prédateurs comme les adultes de M. merluccius (15N = 14,5 ‰). Les grandes différences de 13C au sein des consommateurs primaires attestent de deux différentes sources de nourriture : l'une pélagique composée de matière organique particulaire fraîche sédimentant, qui alimente principalement les suspensivores supra- et épi-benthiques, et le zooplancton et l'autre benthique qui alimente les déposivores. Les changements de régimes alimentaires des prédateurs, l'espèce cible et leurs compétiteurs, au cours de leur vie, se traduisent par des différences isotopiques entre les différentes classes de taille.

Document Type: Research Article

Publication date: January 1, 2005

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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