Zooplankton community dynamics along the bigheaded carp invasion front in the Upper Mississippi River
2022
Tillotson, Nathan A. | Weber, Michael J. | Pierce, Clay L.
Invasive Silver Hypophthalmichthys molitrix and Bighead Carp H. nobilis (collectively bigheaded carp) regularly alter zooplankton communities in lentic systems but dynamics in lotic systems are less understood. Here, we investigated trends in zooplankton communities, densities, and biomass in pools 14–20 of the Upper Mississippi River (UMR) across a gradient of bigheaded carp presence and relative abundance during 2016–2018. We explored the effects of bigheaded carp presence on zooplankton communities using non-metric multidimensional scaling (NMDS) and assessed taxa-specific relationships with bigheaded carp relative abundance using ordinary least-squares regression with an indicator variable for bigheaded carp presence. Zooplankton communities in the UMR were dominated by rotifers and crustacean zooplankton densities were low, making up only 2% of the community density. Zooplankton communities differed where bigheaded carp were present. Density and biomass of cladocerans and copepods were both reduced where bigheaded carp were present but copepods increased with bigheaded carp relative abundance. Ostracod biomass increased in the presence of bigheaded carp whereas rotifers declined with bigheaded carp relative abundance. Low crustacean zooplankton densities in the UMR may limit larval/juvenile fish growth and recruitment regardless of bigheaded carp, but further declines in the crustacean community due to expanding bigheaded carp populations are concerning.
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