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Changes in zooplankton and the phenology of the spiny water flea, Bythotrephes, following its invasion of Harp Lake, Ontario, Canada

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Abstract:

The crustacean zooplankton community of Harp Lake, Ontario, Canada, has changed appreciably since the invasion by the spiny water flea, Bythotrephes. Crustacean species richness has declined, large-bodied Cladocera have replaced small-bodied ones, and there has been a downward trend in the total abundance of zooplankton because copepod abundance has remained stable while Cladoceran abundance has declined. Although the zooplankton community has now been stable for 4 years (1995–1998), the biology of the invader has changed dramatically. In particular, there have been 10-fold differences in the mean annual abundance of Bythotrephes in this 5-year period and substantial changes in the timing of population maxima. We attribute these changes to two factors: (i) transition from a summer to a fall switch from parthenogenesis to gametogenesis and (ii) interannual differences in the thickness of a warm, dark stratum in the lake. We hypothesize that this stratum provides a refuge for Bythotrephes from predation by lake herring, Coregonus artedii.

La communauté des crustacés du zooplancton du lac Harp, en Ontario, Canada, s'est modifiée de façon notable depuis l'invasion de la Puce d'eau épineuse, Bythrotrephes. La richesse en espèces des crustacés a décliné. Les cladocères de grande taille ont remplacé ceux de petite taille et il y a une tendance à la baisse dans l'abondance totale du zooplancton, car, bien que la densité des copépodes soit demeurée constante, celle des cladocères a baissé. La communauté zooplanctonique est restée stable depuis 4 ans (1995–1998); néanmoins, la biologie de l'espèce envahissante a changé de façon spectaculaire. En particulier, il y a eu des variations par un facteur de 10 des densités annuelles moyennes de Bythotrephes pendant cette période de 5 ans et des changements importants dans la phénologie des maximums de densité. Nous attribuons ces changements à deux facteurs : (i) un déplacement de l'été à l'automne du passage de la parthénogenèse à la gamétogenèse et (ii) aux différences inter-annuelles de l'épaisseur d'une strate obscure et chaude dans le lac. Nous croyons que cette strate fournit un refuge à Bythotrephes contre la prédation exercée par le Cisco de lac, Coregonus artedii.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: December 1, 2001

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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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