Whitten, A. L., Jarrin, J. R. M., & McNaught, A. S.
Dreissenid mussels are known to disrupt the base of the food web by filter feeding on phytoplankton; however,
they may also directly ingest zooplankton thereby complicating their effects on plankton communities.
The objective of this study was to quantify the effects of quagga mussel feeding on the composition and size
structure of Lake Michigan zooplankton assemblages. Two mesocosm (six 946 L tanks) experiments were
conducted in summer 2013, using quagga mussels and zooplankton collected near Beaver Island, MI, to examine
the response of zooplankton communities to the presence and absence of mussels (experiment 1) and
varying mussel density (experiment 2). Mesocosms were sampled daily and zooplankton taxa were enumerated
and sized using microscopy and FlowCAM® imaging. In experiment 1, the presence of quagga mussels
had a rapid negative effect on veliger and copepod nauplii abundance, and a delayed negative effect on rotifer
abundance. In experiment 2, mussel density had a negative effect on veliger, nauplii, and copepodite
abundance within 24 h. Multivariate analyses revealed a change in zooplankton community composition with
increasing mussel density. Ten zooplankton taxa decreased in abundance and frequency as quagga mussel
density increased: except for the rotifer Trichocerca sp., treatments with higher mussel densities (i.e., 1327,
3585, and 5389 mussels/m2) had the greatest negative effect on small-bodied zooplankton (≤ 128 μm). This
study confirms results from small-scale (≤ 1 L) experiments and demonstrates that quagga mussels can alter
zooplankton communities at mesoscales (~ 1000 L), possibly through a combination of direct consumption
and resource depletion.