Eicosapentaenoic acid limitation decreases weight and fecundity of the invading predator Bythotrephes longimanus

Bythotrephes longimanus is an invasive predatory cladoceran that is negatively impacting North American zooplankton in the Laurentian Great Lakes and on the Canadian Shield. Concurrently, algal community composition, which affects zooplankton food quality, is changing in many lakes of the Canadian Shield. The n-3 fatty acid eicosapentaenoic acid (EPA) is highly retained in Bythotrephes, but the effects of EPA limitation on Bythotrephes’ population dynamics are unknown. To test the hypothesis that EPA limitation results in decreased weight and fecundity of Bythotrephes, the green alga Scenedesmus obliquus was cultured in the laboratory, split into EPA-enriched lines and un-enriched controls, then fed to Daphnia ambigua, which were in turn offered to juvenile Bythotrephes. Bythotrephes consuming EPA-enriched daphniids were heavier and had larger clutch sizes than those consuming control daphniids. Both diets supported ontogenesis, but not brood release, of Bythotrephes. To understand why laboratory-reared Bythotrephes did not release broods, we compared their fatty acid profiles with those of field-collected specimens, and found that they were EPA impoverished compared with field-collected conspecifics. Our results suggest that EPA availability influences Bythotrephes population dynamics, establishment success and impacts in nature.