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Experimental determination of the sources of otolith carbon and associated isotopic fractionation

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Otolith stable carbon isotope ratios provide a unique and widely applicable environmental record. Unfortunately, uncertainty regarding the proportion of otolith carbon that derives from metabolized food versus dissolved inorganic carbon (DIC) in the water currently limits utilization of this marker. We manipulated the 13C of food and ambient DIC in a factorial design with juvenile rainbow trout (Oncorhynchus mykiss). At the activity levels and total metabolic rates characteristic of fish in this study, 17% (±3% standard error, SE) of otolith C was metabolically derived, while >80% was derived from DIC in ambient water. We also estimated isotopic enrichment factors associated with physiological carbon transformations by measuring 13C of blood and endolymph (which closely tracked otolith 13C). There was substantial depletion in 13C of blood relative to C sources (εblood–sources = –16.9‰ ± 1.1‰ SE), but substantial enrichment in 13C in otolith relative to blood (εoto–blood = 13.3‰ ± 1.3‰ SE). Net isotopic enrichment between sources and the otolith was therefore slightly negative. Most of the isotopic enrichment between the blood and the otolith was associated with the movement of C from blood to endolymph, while enrichment associated with the precipitation of otolith aragonite from the endolymph was small.

Les rapports des isotopes stables de carbone dans les otolithes représentent une rétrospective des conditions du milieu qui est à la fois exceptionnelle et d'utilisation multiple. Malheureusement, des incertitudes concernant la proportion du carbone dans les otolithes qui provient de la nourriture métabolisée par rapport au carbone inorganique dissous (DIC) dans l'eau freinent actuellement l'utilisation de ce marqueur. Nous avons fait varier le 13C de la nourriture et du DIC ambiant selon un plan d'expérience factoriel avec de jeunes truites arc-en-ciel (Oncorhynchus mykiss). Aux niveaux d'activité et aux taux métaboliques caractéristiques des poissons utilisés dans notre étude, 17 % (±3 % erreur type, ET) du C des otolithes provient du métabolisme, alors que >80 % vient du DIC de l'eau ambiante. Nous avons aussi mesuré les facteurs d'enrichissement métabolique associés aux transformations physiologiques du carbone, en déterminant le 13C du sang et de l'endolymphe (qui suit de près le 13C des otolithes). Il y a une perte substantielle de 13C dans le sang par rapport aux sources de C (εsang–sources = –16,9‰ ± 1,1‰ ET), mais aussi un enrichissement important de 13C dans les otolithes par rapport au sang (εoto–sang = 13,3‰ ± 1,3‰ ET). L'enrichissement isotopique net des sources vers les otolithes est donc légèrement négatif. La majorité de l'enrichissement isotopique entre le sang et les otolithes est associée au passage du C du sang vers l'endolymphe, alors que l'enrichissement dû à la précipitation d'aragonite dans les otolithes depuis l'endolymphe est faible.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: January 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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