Direct and Indirect Effects of Invasive Asian Carp on Native Communities

Invasive species may alter primary productivity and nutrient content in native ecosystems, affecting condition of native species.  For example, planktivorous Bighead (Hypophthalmichthys nobilis) and Silver Carp (H. molitrix), collectively Asian Carp, may alter freshwater trophic dynamics, reduce phytoplankton and zooplankton, and compete with native Gizzard Shad (Dorosoma cepedianum). To examine how Asian Carp affect zooplankton, system primary productivity, and Gizzard Shad, we conducted a series of pond mesocosm experiments with varying densities of Gizzard Shad and Bighead and Silver Carp.  Ponds were sampled weekly for zooplankton abundance, chlorophyll a concentration, detrital N and P concentrations, and water column NH₄, NO₃, and PO₄ concentrations throughout each experiment.  Preliminary results suggest that Asian Carp presence does not significantly affect Gizzard Shad growth, although zooplankton density declined in the presence of Asian Carp over time.  This result could be due to a dietary shift by Gizzard Shad from zooplankton to detritus in the presence of Asian Carp.  Additionally, although chlorophyll a and water NH₄, NO₃, and PO₄ concentrations do not appear to differ in the presence or absence of Asian Carp, these fish may alter detrital quality, thereby providing a high quality alternative food source for Gizzard Shad.