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Effects of Bythotrephes on the trophic position of native macroinvertebrates

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Abstract:

We measured the 15N and 13C stable isotopes of pelagic invertebrate predators in six central Ontario lakes, three invaded by Bythotrephes and three not invaded, to determine the effects of Bythotrephes invasion on diet overlap and trophic position of the predators. Seasonally averaged, lake-specific isotope signatures of bulk zooplankton were used as the isotopic baseline for determining nitrogen-based trophic position or carbon enrichment of the predators. Trophic positions of native Chaoborus, Leptodora, and Mysis in invaded lakes were not elevated compared with noninvaded lakes, suggesting that these predators do not feed directly on Bythotrephes. Nitrogen signatures of Mysis and Chaoborus were similar as were those of Leptodora and Bythotrephes, suggesting that invasion impacts will be greatest on Leptodora as has been observed. The trophic position of large Mysis was generally the highest and most variable of all predators, probably because it feeds on copepods that are more enriched in the heavier nitrogen isotope than bulk zooplankton and because Bythotrephes tends to decrease the ratio of cladocerans to copepods in invaded zooplankton communities.

Nous avons mesuré les 15N et 13C des isotopes stables des invertébrés prédateurs pélagiques dans six lacs du centre de l’Ontario, trois envahis par Bythotrephes et trois non affectés, afin de déterminer les effets de l’invasion de Bythotrephes sur le chevauchement des régimes alimentaires et la position trophique des prédateurs. Les signatures moyennes saisonnières du zooplancton global de chacun des lacs servent de référence isotopique de base pour déterminer la position trophique en fonction de l’azote et l’enrichissement en carbone des prédateurs. Les positions trophiques des Chaoborus, Leptodora et Mysis indigènes des lacs envahis ne sont pas plus élevées que celles des lacs non envahis, ce qui fait croire que ces prédateurs ne se nourrissent pas directement de Bythotrephes. Les signatures d’azote de Mysis et de Chaoborus sont semblables, comme le sont celles de Leptodora et de Bythotrephes, ce qui laisse croire que les impacts des invasions seront plus importants sur les Leptodora, ce qui s’est avéré le cas. La position trophique des Mysis de grande taille est généralement la plus élevée et la plus variable de celles de tous les prédateurs, probablement parce qu’ils se nourrissent de copépodes qui sont plus enrichis en l’isotope plus lourd d’azote que le zooplancton global et parce que Bythotrephes tend à faire diminuer le rapport cladocères à copépodes dans les communautés zooplanctoniques envahies.

Document Type: Research Article

Publication date: January 1, 2010

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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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