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Stable isotopes as an indicator of diet in omnivorous crayfish (Pacifastacus leniusculus): the influence of tissue, sample treatment, and season

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Abstract:

Stable isotopes have been used to analyse food webs and (or) trace movements of animals for about 30 years. There has been some debate on the use of different tissues and treatments before isotope analysis, as well as on seasonal effects. We found different crayfish (Pacifastacus leniusculus) tissues (muscle, hepatopancreas, exoskeleton, gill, and whole body) to have different isotope values. Lipid extraction made whole-body carbon isotope values higher but had no effect on nitrogen isotope values. Acidification made whole-body isotope values lower. For crayfish, there was no seasonal or interannual variation in isotope values. In contrast to studies based on gut content analysis, we found adult crayfish to be at least as carnivorous as young-of-the-year crayfish. Earlier studies often have assumed that each food source contributes both nitrogen and carbon in equal proportions. Omnivores do not fit easily into this view. We suggest that nitrogen and carbon in an organism could come from different sources. Adopting this view for a pond food web could render crayfish both predators and detritivores as crayfish prey on nitrogen sources (other invertebrates) and consume large amounts of detritus to satisfy their carbon demand.

Il y a environ 30 ans qu'on utilise les isotopes stables pour analyser les réseaux alimentaires et (ou) suivre les déplacements des animaux. Le choix des divers tissus, les préparations antérieures à l'analyse isotopique et les effets saisonniers ont fait l'objet de nombreuses discussions. Dans notre étude sur l'écrevisse Pacifastacus leniusculus, les différents tissus (muscle, hépatopancréas, exosquelette, branchie et corps entier) ont des valeurs isotopiques différentes. L'extraction des lipides accroît les valeurs des isotopes de carbone dans le corps entier, mais reste sans effet sur les isotopes d'azote. L'acidification réduit les valeurs isotopiques du corps entier. Chez l'écrevisse, il n'y a pas de variation des valeurs isotopiques d'une saison à l'autre ou d'une année à l'autre. Contrairement aux analyses des contenus du tube digestif, notre étude trouve les écrevisses adultes au moins aussi carnivores que les jeunes écrevisses de l'année. Les études antérieures ont souvent présupposé que chaque source dans le régime alimentaire fournit du carbone et de l'azote en proportions égales. Les omnivores ne cadrent pas facilement avec cette supposition. Nous croyons que l'azote et le carbone dans un organisme peuvent provenir de sources différentes. Si nous appliquons cette interprétation à un réseau alimentaire d'étang, les écrevisses deviennent à la fois des prédateurs et des détritivores puisqu'elles font de la prédation sur les sources d'azote (les autres invertébrés) et consomment de grandes quantités de détritus afin de satisfaire leurs besoins en carbone.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: April 1, 2006

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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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