Zooplankton community composition across a gradient of Asian carp densities and pre- and post-invasion within the Illinois River, USA

Invasive Asian carps have established populations in many areas within the Upper Mississippi River basin and may alter zooplankton community composition and densities due to their miniscule filtering capacities.  We tested whether Asian carps have influenced zooplankton assemblages prior to and following their establishment within the La Grange Reach, Illinois River and in six reaches of the Illinois River that varied in Asian carp abundances.  We compared archived zooplankton samples collected in the mid-1990’s with those collected in 2009 for our pre- and post- Asian carp establishment analysis and collected zooplankton samples biweekly in June-July, 2009 for our comparative analysis.  Prior to the Asian carp invasion, the zooplankton community was dominated by cladocerans and copepods.  After Asian carp establishment, zooplankton densities increased and were dominated by rotifers.  In reaches with greater abundances of Asian carps, densities of zooplankton were greater and also dominated by rotifers.  In the uppermost reaches of the Illinois River where Asian carp densities are not as high, zooplankton community composition and density was more commensurate with assemblages found prior to the Asian carp invasion.  Our results suggest that Asian carps may be ecosystem engineers capable of creating conditions more favorable for their survival and growth.