Linking Nutrient Dynamics to Assess the Impact of Invasive Asian Carp on Native Communities

Introduced species may alter primary productivity and nutrient content in invaded ecosystems, affecting condition of native species.  In the central U.S., Asian Carp (Hypophthalmichthys spp.) may alter nutrient pathways, plankton communities, and native Gizzard Shad (Dorosoma cepedianum) condition and abundance. We conducted a series of pond mesocosm experiments to assess competition between Gizzard Shad and Silver Carp (H. Molitrix) and effects of Silver Carp decomposition on native communities.  Ponds were sampled weekly for variables including zooplankton abundance, chlorophyll a concentration, water NH₄, NO₃, and PO₄ concentrations, and detrital nutrient concentrations.  Guts from each species were sampled at the conclusion of the experiment.  Asian Carp presence did not significantly affect gizzard shad growth, although zooplankton density and chlorophyll a concentration declined with Asian Carp presence.  Gizzard shad consumed mostly detritus, indicating a lack of competition.  Although Asian Carp do not appear to affect water NH₄, NO₃, and PO₄ concentrations, they may enhance detrital quality, through excretion or carcass decomposition, thereby providing a high quality food source for Gizzard Shad.