Effects of adult common carp (Cyprinus carpio) on multiple trophic levels in shallow mesocosms

We examined the effects of adult common carp (Cyprinus carpio) on shallow aquatic ecosystems and compared the effects with those of a native benthic fish, channel catfish (Ictalurus punctatus). Experimental ponds contained enclosures (0.06 ha) with a low carp biomass (174 kg·ha^-1), high carp biomass (476 kg·ha^-1), high catfish biomass (416 kg·ha^-1), and no fish. We measured abiotic factors (turbidity, suspended solids, total phosphorus), as well as effects on adjacent trophic levels (aquatic macrophytes, zooplankton, and aquatic macroinvertebrates) from July to September. Common carp was positively related to total phosphorus, turbidity, suspended solids, and zooplankton biomass, and negatively related to macrophyte and macroinvertebrate abundance. Suspended solids in the carp treatments consisted primarily of inorganic particles. Carp were either positively or negatively related to phytoplankton, depending on zooplankton abundance. A high biomass of carp had greater effect on nutrients, turbidity, and suspended solids than a low biomass. Channel catfish was positively related to total phosphorus concentrations and altered zooplankton composition, but did not affect turbidity, suspended solids, macroinvertebrates, and macrophytes. These results suggest that common carp have a stronger influence on water quality and aquatic community structure than benthic fish native to North America.