Competitive Interactions Between Common Carp and Bighead Carp

Invasive species are a driving force of global ecosystem change and competitive interactions with other species are likely.  We investigated competitive interactions between two highly invasive species, common carp (Cyprinus carpio) and bighead carp (Hypophthalmichthys nobilis).  Before undergoing an ontogenetic shift to benthic macroinvertebrates, common carp rely on zooplankton until around 100 mm TL.  The potential for competitive interactions exist as bighead carp are obligate zooplanktivores.  In a replicated mesocosm experiment, we manipulated densities of juvenile common and bighead carp to infer the per-capita effects of inter- and intraspecific competition, as well as community effects by these two species.  We found that intraspecific competition had a greater influence on both common and bighead carp than interspecific competition.  Both species had strong negative effects on zooplankton density. Bighead carp also appeared to utilize rotifer populations as a food source, while the presence of common carp had a negative influence on benthic taxa richness.  The results of the study suggest common and bighead carp can coexist and appear to partition food resources during scarcity.