| The Ponto-Caspian invader Bythotrephes longimanus (commonly known as the spiny water flea; herein Bythotrephes ), continues to expand throughout North America, having been identified in > 170 water bodies. As a voracious predator, Bythotrephes has had profound impacts on native zooplankton abundance, species richness, diversity, and community size structure. Yet the open water habitats of the Canadian Shield, where the majority of new invasions are occurring, are in a state of flux. Among the many changes are rising summer water temperatures, declining waterborne calcium (Ca) levels, decreasing total phosphorous (which will likely impact primary productivity and herbivorous zooplankton, Bythotrephes' primary prey), and deteriorating algal food quality with respect to fatty acids.;Bythotrephes' unintentional introduction and subsequent spread have served as a prime opportunity for an in-depth analysis of the invasion process. This study is one of the very few examining in detail a suite of factors governing the survival, growth, and reproduction of this species. Much of the information presented here will be useful for modeling and management efforts.;What remains unclear is how these factors, singly or in combination, might affect the continuing establishment of Bythotrephes populations. It was my goal to investigate these knowledge gaps through controlled laboratory studies with reinforcing arguments from field observations, where available. I began by devising a culturing technique for Bythotrephes , a species that is notoriously difficult to rear in the laboratory, and finding its temperature optima (Chapter 2). Next, I examined the potential impacts of low Ca on Bythotrephes by determining its somatic Ca content, conducting a life table response experiment in which a cohort of Bythotrephes was reared at differing Ca concentrations, and by examining its distribution in relation to Ca in Norway, where it has been established for millennia (Chapter 3). After deducing that Bythotrephes will likely not be directly affected by falling Ca concentrations, I go on to explore the possible joint impacts of low Ca and Bythotrephes presence on native Daphnia, which have relatively high Ca demands. It became evident that Bythotrephes' ability to survive and reproduce is highly influenced by prey availability. Therefore, the effects of prey quantity and quality (in terms of the omega-3 fatty acid eicosapentaenoic acid, or EPA) on Bythotrephes life history and demography were investigated (Chapters 4 and 5, respectively). Not surprisingly, increasing prey quantity not only improved Bythotrephes population growth rates, it resulted in larger offspring and shorter generation times. Prey quality plays a paradoxical role; while supplementing daphniid prey with EPA made predation by juvenile Bythotrephes a challenge, the addition of this compound fosters increased clutch size in adult Bythotrephes. Finally, the results of these studies along with additional observations on the autecology of this species are summarized, and approaches for management are discussed (Chapter 6). |
