The predatory zooplankton, Bythotrephes longi-manus (Leydig 1860) (Crustacea: Cercopagidae), was first observed in the Laurentian Great Lakes in the early 1980s (Johannsson et al. 1991). Its introduction was likely the result of accidental transport in ship ballast water carried from Eurasia (Sprules et al. 1990). Bythotrephes has since spread to at least 40 smaller, inland lakes across North America (MacIsaac et al. 2000). These secondary invasions repeatedly demonstrate the ability of Bythotrephes to overcome land barriers and exploit a diverse group of lake ecosystems. Bythotrephes reproduce by cyclic parthenogenesis. Population development each spring begins with emergence of animals from diapausing eggs in the sediments. Diapausing eggs not only facilitate inter-annual persistence of Bythotrephes within invaded lakes, but they are thought to aid colonization of new ecosystems. Knowledge of the diapausing egg is thus imperative to understanding the ecology of established populations as well as range expansion of this invader. This contribution examines the dynamic relationship between demographics of the planktonic stage of Bythotrephes and the sediment diapausing egg bank over an annual cycle in Island Lake Reservoir, Minnesota, USA.
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