Effects of Common Carp (Cyprinus Carpio) in a Shallow, Temperate Freshwater Lake

Common carp (Cyprinus carpio L.) can significantly affect plant and animal communities, as well as nutrient cycling in shallow, freshwater environments. Carp mechanically damage plants by uprooting and/or breaking stems, as well as increasing turbidity and nutrient cycling through sediment resuspension. Increased turbidity reduces light penetration in the water column and can reduce macrophyte abundance. These changes decrease refugium for invertebrates and juvenile fish. We used two types of cages to determine the direct and indirect effects of carp on macrophytes and food web dynamics. The first experiment was conducted in 5m x 5m cages with carp (at ambient densities) and no carp controls. A second experiment, using 15m x 5m exclosures, was also performed to exclude carp from existing macrophyte beds. We used threesided cages of the same size open to the lake as controls (carp present). We found changes in macrophyte abundance and species composition, as well as abundance and diversity of invertebrates in our small enclosures. In our large exclosures, carp significantly reduced macrophyte stem length and biomass relative to controls. However, in the large exclosures, we found invertebrate diversity, total abundance and species richness did not differ between treatments.