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Community interactions affecting the relative abundances of native and invasive amphipods in the St. Lawrence River

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Abstract:

The Eurasian amphipod Echinogammarus ischnus is reportedly replacing the common native amphipod Gammarus fasciatus in the Great Lakes – St. Lawrence River system. A potential mechanism for this replacement is competition mediated by resident species. Other Eurasian invaders, dreissenid mussels (Dreissena polymorpha and Dreissena bugensis), dominate rocky substrates throughout the system and might be promoting the rapid expansion of E. ischnus by providing habitat and refugia from predation. Using an in-situ predator-exclusion experiment, we tested the hypothesis that E. ischnus is better able than G. fasciatus to use Dreissena spp. colonies as refugia and thus is less susceptible to predators in the St. Lawrence River. Co-occurring E. ischnus and G. fasciatus showed similar increases in density in the presence of Dreissena spp., in spite of E. ischnus having evolutionary experience with Dreissena spp. Predators reduced the density of both amphipod species, but E. ischnus was more susceptible to predation on dreissenid substrates, which suggests that predation mediates the coexistence of G. fasciatus and E. ischnus in the river.

L'amphipode eurasiatique Echinogammarus ischnus est, rapporte-t-on, en train de remplacer l'amphipode indigène commun Gammarus fasciatus dans le système des Grands Lacs et du Saint-Laurent. Un mécanisme possible de cette substitution est une compétition par l'intermédiaire des espèces résidantes. D'autres envahisseurs eurasiatiques, les bivalves dreissénidés (Dreissena polymorpha et Dreissena bugensis), dominent les substrats rocheux dans tout le système et peuvent peut-être favoriser l'expansion rapide d'E. ischnus en fournissant un habitat et des refuges contre la prédation. À l'aide d'une expérience in situ d'exclusion des prédateurs, nous avons éprouvé l'hypothèse selon laquelle, dans le Saint-Laurent, E. ischnus est plus habile que G. fasciatus à utiliser les colonies de Dreissena spp. comme refuges et il est moins vulnérable aux prédateurs. Les E. ischnus et les G. fasciatus en cohabitation montrent les mêmes accroissements de densité en présence de Dreissena spp., bien qu'E. ischnus ait une expérience de cohabitation avec Dreissena spp. au cours de son évolution. Les prédateurs réduisent la densité des deux espèces, mais E. ischnus est plus vulnérable à la prédation sur les substrats de dreissenidés, ce qui laisse croire que la prédation explique la coexistence de G. fasciatus et d'E. ischnus dans le fleuve.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: May 1, 2005

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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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