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Multivariate analysis of stable-isotope ratios to infer movements and utilization of estuarine organic matter by juvenile weakfish (Cynoscion regalis)

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Abstract:

Canonical discriminant analysis of the natural carbon, nitrogen, and sulfur stable isotopes in tissues of young weakfish (Cynoscion regalis) captured in Delaware Bay was used to infer movements of juveniles and to estimate the utilization of estuarine organic matter in this marine transient species. Two gradients emerged in the data. The first was associated with contributions from tidal salt marsh macrophytes, Spartina alterniflora in the polyhaline lower Bay and Phragmites australis in the brackish upper Bay. The second was associated with the expected change in phytoplankton carbon-isotope values along the salinity gradient in addition to the availability of macrophyte-derived organic matter within the Bay. The separation of the gradients reflected differences in the relative contribution of phytoplankton to weakfish secondary production in open waters versus marsh habitats. As they grew, discrepancies between the anticipated isotopic signatures of juvenile weakfish collected in a specific habitat and their actual signatures were interpreted as down-bay movements based on known life-history patterns. The size-specific differences in the isotopic signatures of weakfish suggested that stable-isotope data can be used to gauge the relative magnitude of marsh-derived organic matter exported from Delaware Bay via movements of juveniles out of the estuary.

Une analyse discriminante canonique des isotopes stables naturels de carbone, d'azote et de soufre dans les tissus de jeunes acoupas royaux (Cynoscion regalis) capturés dans la baie de la Delaware nous a servi à retracer les déplacements des jeunes et à estimer l'utilisation de la matière organique estuarienne chez cette espèce marine de passage. Deux gradients apparaissent dans les données, un premier associé aux contributions des macrophytes des marais salés affectés par la marée, Spartina alternifolia, dans la baie inférieure polyhaline et Phragmites australis, dans la baie supérieure saumâtre. Le second gradient est associé au changement attendu des values isotopiques du carbone phytoplanctonique en fonction du gradient de salinité, en plus de la disponibilité de la matière organique provenant des macrophytes à l'intérieur de la baie. La séparation des gradients est le reflet de différences dans les contributions relatives du phytoplancton à la production secondaire des acoupas dans les eaux du large et dans les habitats de marais. Durant la croissance, les écarts entre les signatures isotopiques anticipées des jeunes acoupas récoltés dans un habitat particulier et les signatures réelles s'interprètent comme des déplacements vers la baie inférieure basés sur des patterns connus du cycle biologique. Les différences de signatures isotopiques des acoupas reliées à la taille indiquent que les données sur les isotopes stables pourraient servir à évaluer l'importance relative de la matière organique provenant des marais qui est exportée de la baie de la Delaware par les déplacements des acoupas hors de l'estuaire.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: October 1, 2004

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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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