Where Have All the Rotifers Gone? Zooplankton Community Patterns in Lake Champlain from 1992–2001

Abstract

This study focused on zooplankton community patterns in five Lake Champlain sites from 1992-2001. Analysis of summer (July-August) zooplankton data demonstrates a decline in rotifer species abundance and richness at all study sites. Long-term patterns show a shift in zooplankton community composition from dominance by rotifers, to increased densities of cyclopoids in the late 1990’s. Between 1994 and 1997 rotifer species richness had declined by 5–9 species at all study sites. Some rotifer taxa (Synchaeta spp., Filinia spp., and Lecane spp.) have not been observed at any study site since 1996. Rotifer species composition has shifted from taxa indicative of eutrophic conditions to those, characteristic of oligotrophic waters. Coincidental with the shift in community composition is the introduction and proliferation of zebra mussels into Lake Champlain in the mid 1990’s. Possible zebra mussel mediated effects or other causes for the observed community shifts are discussed.