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Physical factors affecting the relative abundance of native and invasive amphipods in the St. Lawrence River

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The Ponto-Caspian amphipod Echinogammarus ischnus (Stebbing, 1899) is reportedly replacing the North American amphipod Gammarus fasciatus Say, 1818, in the lower Great Lakes, but the two species appear to coexist in the upper St. Lawrence River several years after invasion by E. ischnus. A multi-site survey in the river between Lake Ontario and Montreal (Quebec) found that E. ischnus and G. fasciatus respond differently to substrate characteristics, water chemistry variables, and current velocity. Both species increase in abundance in the presence of dreissenid mussels. However, E. ischnus density is positively correlated with current velocity and an increasing proportion of gravel-sized sediment, while G. fasciatus density is positively correlated with benthic filamentous algal (Cladophora spp.) biomass, macrophyte biomass, and pH. Habitat heterogeneity within the river may be promoting the coexistence of native and exotic amphipods by allowing them to segregate along physicochemical gradients.

L'amphipode ponto-caspien Echinogammarus ischnus (Stebbing, 1899) est, rapporte-t-on, en train de remplacer l'amphipode nord-américain Gammarus fasciatus Say, 1818 dans les Grands Lacs inférieurs. Les deux espèces semblent cependant coexister dans le cours supérieur du Saint-Laurent plusieurs années après l'invasion de E. ischnus. Un inventaire dans de multiples sites du fleuve entre le lac Ontario et Montréal (Québec) indique que E. ischnus et G. fasciatus réagissent différemment aux caractéristiques du substrat, aux variables chimiques de l'eau et à la vitesse de courant. La densité des deux espèces croît en présence des bivalves dreissenidés. Cependant, la densité d'E. ischnus est en corrélation positive avec la vitesse du courant et une proportion accrue des gravillons dans les sédiments, alors que la densité de G. fasciatus est en corrélation positive avec la biomasse des algues filamenteuses benthiques (Cladophora spp.), la biomasse des macrophytes et le pH. L'hétérogénéité de l'habitat de la rivière peut sans doute favoriser la coexistence des amphipodes indigènes et exotiques en leur permettant de s'isoler le long de gradients physicochimiques.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: December 1, 2004

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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