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Trophic studies in a high-latitude fjord ecosystem — a comparison of stable isotope analyses (13C and 15N) and trophic-level estimates from a mass-balance model

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Abstract:

Stable isotopes of 13C and 15N were used to examine food sources and trophic structure of 65 taxa, representing 19 ecological groups, in a high-latitude ecosystem. Discrimination was made between pelagic and benthic carbon sources, where feeding in most cases reflected the habitat. Trophic levels from these analyses, TLN, were compared with corresponding levels estimated by an Ecopath mass-balance model, TLE, constructed independently of the isotope data. The good correlation between the two methods (r2 = 0.72) supports the diet composition and the grouping of taxa into ecological groups in the model. However, when estimates diverged, this was often explained by the analyses of few taxa, taxa that were not the most representative for the group, or the analyses of specimens from a limited size range. Some assumed detrivores were assigned high TLN in favour of an abundant microbial community in the sediments. High TLN estimates for many invertebrate taxa, combined with relatively low TLN for fishes, suggest that parts of the benthic food web are decoupled from the classical food web.

Les isotopes stables de 13C et de 15N nous ont servi à examiner les sources alimentaires et la structure trophique chez 65 taxons, représentant 19 groupes écologiques, dans un écosystème de haute latitude. Il a été possible de discriminer entre les sources pélagiques et benthiques de carbone et l’alimentation reflète l’habitat, dans la plupart des cas. Nous avons comparé les niveaux trophiques obtenus dans ces analyses, TLN, aux niveaux correspondants, TLE, estimés par le modèle de bilan de masse d’Ecopath construit indépendamment des données isotopiques. La forte corrélation entre les deux méthodes (r2 = 0,72) confirme la composition des régimes alimentaires et le regroupement des taxons en groupes écologiques dans le modèle. Cependant, les cas de divergence entre les estimés s’expliquent souvent par l’analyse d’un petit nombre de taxons, celle de taxons qui ne sont pas les plus représentatifs du groupe ou celle de spécimens d’une gamme restreinte de tailles. Certains détritivores présumés ont obtenu une valeur élevée de TLN , ce qui laisse croire à une abondante communauté microbienne dans les sédiments. Les valeurs élevées de TLN estimées chez plusieurs invertébrés, combinées aux valeurs relativement basses de TLN chez les poissons semblent indiquer que certaines parties du réseau alimentaire sont découplées par rapport aux réseaux alimentaires classiques.

Document Type: Research Article

Publication date: December 1, 2008

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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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