| dc.description.abstract | Invasive species are a major threat to aquatic ecosystems, costing an estimated $3.6
billion in impacts across Ontario. In particular, the predatory cladoceran Bythotrephes
cederströmii (Bythotrephes hereafter) has had significant trophic impacts on invaded
ecosystems, such as decreasing zooplankton density and biomass. Changes to the
zooplankton community can impact ecosystem energy rates and dominant pathways of
transfer to other organisms in a “middle-out” trophic cascade, altering predator-prey
dynamics for both algae and fish. Here, I used relevant zooplankton abundances
characteristic of invaded and non-invaded lakes and a bioenergetics model to evaluate
whether the Bythotrephes-induced changes to native zooplankton is expected to alter
larval walleye consumption (and therefore rates of growth). I then used observational
data to evaluate the impact Bythotrephes has on the zooplanktivorous young-of-year
(YOY) walleye. I used a back-calculation model and linear mixed effect modeling to
evaluate differences in YOY walleye growth between invaded and non-invaded
waterbodies, as well as within invaded waterbodies pre- and post-invasion. In the first
data chapter (chapter 2), a functional response and bioenergetics model revealed larval
walleye grow slower in invaded mesotrophic lakes compared to non-invaded mesotrophic
lakes, and models suggest they are unlikely to survive in invaded oligotrophic lakes based
on available zooplankton. In the second data chapter (chapter 3), I found that relative to
similar sized non-invaded lakes, YOY walleye grow slower in small, invaded lakes,
whereas large lakes show less severe effects. Overall, Bythotrephes has differing impacts
on YOY walleye growth depending on lake characteristics such as lake size and trophic
state. As growth rates are ultimately linked to reproduction, recruitment, and production, understanding growth rates post-invasion is essential for fisheries managers to develop
and anticipate adaptive management strategies. | en_US |
