Ichthyochory in a temperate river system by common carp (Cyprinus carpio)

Some fish are important dispersal vectors of aquatic plants (i.e., ichthyochory), yet few examples have been documented outside of the Neotropics. Although highly modified and degraded, the upper Illinois River Waterway supports common carp (Cyprinus carpio) populations and abundant aquatic vegetation. As common carp have been previously documented to consume aquatic vegetation seeds, we assessed diets to determine the potential for common carp to function as dispersal vectors for aquatic vegetation seeds that may be important for restoration of rivers and floodplain wetlands. Whole seeds occurred at a high frequency and 42 seed taxa were discovered in the digestive system of common carp. Electivity analysis indicated that most seeds present were incidentally ingested; however, common carp diets contained seeds of wild celery (Vallisneria americana) at rates greater than expected by random chance. Our study indicates common carp may fill a similar functional role of seed dispersal for aquatic plant communities in temperate large river systems as they do for fruiting plants in the Neotropics. Our results highlight an understudied aspect of temperate freshwater ecology – fish as a potential influence on plant dynamics and resources in rivers. Fish-mediated seed dispersal has important but poorly understood implications and should be further explored.