Abstract
Invasive species represent a threat to aquatic ecosystems globally; however, impacts can be heterogenous across systems. Documented impacts of invasive zebra mussels (Dreissena polymorpha) and spiny water fleas (Bythotrephes cederströmii; hereafter Bythotrephes) on native fishes are variable and context dependent across locations and time periods. Here, we use a hierarchical Bayesian analysis of a 35-year dataset on two fish species from 9 lakes to demonstrate that early life growth of ecologically important fishes are influenced by these aquatic invasive species. Walleye (Sander vitreus) in their first year of life grew more slowly in the presence of either invader after correcting for temperature (measured by degree days), and were on average 12 or 14% smaller at the end of their first summer following invasion by Bythotrephes or zebra mussels, respectively. Yellow perch (Perca flavescens) growth was less affected by invasion. Yellow perch on average grew more slowly in their first year of life following invasion by zebra mussels, although this effect was not statistically distinguishable from zero. Early life growth of both walleye and yellow perch was less tightly coupled to degree days in invaded systems, as demonstrated by increased variance surrounding the degree day-length relationship. Smaller first-year size is related to walleye survival and recruitment to later life stages and has important implications for lake food webs and fisheries management. Future research quantifying effects of zebra mussels and Bythotrephes on other population-level processes and across a wider gradient of lake types is needed to understand the mechanisms driving observed changes in walleye growth.
Highlights
Zebra mussels (Dreissena polymorpha) and spiny water fleas (Bythotrephes cederstromii; Korovchinsky and Arnott 2019; hereafter Bythotrephes) are aquatic invasive species (AIS) that transform freshwater ecosystems
We use a 35-year dataset from 9 lakes to demonstrate that early life growth of an important top predator, walleye, is influenced by these aquatic invasive species
Growth responses varied among lakes, years, and individuals, and suggest some degree of decoupling of growth from temperature in systems invaded by zebra mussels
Summary
Zebra mussels (Dreissena polymorpha) and spiny water fleas (Bythotrephes cederstromii; Korovchinsky and Arnott 2019; hereafter Bythotrephes) are aquatic invasive species (AIS) that transform freshwater ecosystems. Zebra mussels are filter feeders that reduce pelagic primary production and increase water clarity (Macisaac 1996; Strayer et al 1999; Karatayev et al 2002) They indirectly affect zooplankton biomass, size structure, and community composition (Pace et al 1998; Idrisi et al 2001; Higgins and Vander Zanden 2010). Bythotrephes are predatory zooplankters that reduce native zooplankton biomass and can shift zooplankton community composition to prey species that are suboptimal for fish via both direct predation and indirect effects (Yan and Pawson 1997; Hoffman et al 2001; Barbiero and Tuchman 2004; Fernandez et al 2009; Rennie et al 2011; Kerfoot et al 2016) These changes in the zooplankton community can decrease water clarity via a trophic cascade (Walsh et al 2016), effects on phytoplankton communities vary among lakes (Strecker et al 2006, 2011)
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