Ecological impacts of an exotic benthivorous fish in wetlands : a comparison between common carp (Cyprinus carpio L.) additions in large experimental wetlands and small mesocosms in Delta Marsh, Manitoba

Abstract

I examined the impacts of an exotic benthivorous fish, the common carp (Cyprinus carpio L.), in large (5-7 ha) experimental wetlands and in small (5 x 5 m) mesocosms located in Delta Marsh, Manitoba, Canada. In addition to following the impacts of common carp on water quality, sedimentation, and submerged macrophyte biomass, the impacts of common carp on phytoplankton, zooplankton, benthic invertebrates, and forage fish populations in the small mesocosms were intensively studied. As carp are often the dominant fish species found in degraded aquatic systems, the interaction between nutrient loading and carp, and the resulting impacts on important biotic and abiotic components were investigated through the small mesocosm experiments. In both the large experimental wetland cells and the small mesocosms common carp significantly increased turbidity and suspended solid concentrations, sedimentation rates, chlorophyll a concentrations, and reduced submerged macrophyte biomass and light penetration. These results indicate that carp can significantly affect water quality and nutrient cycling in wetlands and lakes of Manitoba, even at relatively conservative densities. However, carp only induced a shift to the turbid state in the small mesocosm experiments. Failure to shift the large wetland cells to the phytoplankton dominated state was likely due to high DOC concentrations and submerged macrophyte biomass in these large ponds, which reduced the ability of the common carp to increase phytoplankton biomass. At high densities of common carp in the fertilized enclosures, phytoplankton biomass was greatly reduced relative to the no carp and low carp treatments...