The Role of Common Carp in Shallow Lake Ecosystems

Common carp Cyprinus carpio influence aquatic ecosystems through middle-out effects.  Previous work on the effects of common carp primarily focused on invertebrates and water quality at small spatial scales (i.e., mesocosms) with fewer studies identifying their influence on aquatic biota with whole-lake experiments.  We used mensurative and manipulative approaches to study the effects of common carp on shallow lakes in the Nebraska Sandhills.  The mensurative approach compared fish populations of five different species (yellow perch Perca flavescens, bluegill Lepomis macrochirus, northern pike Esox lucius, largemouth bass Micropterus salmoides, black bullhead Amerius melas), chemical, physical, and invertebrate densities in eight lakes with and eight lakes without common carp.  Largemouth bass, black bullhead, and bluegill appeared to be more affected, some positively and some negatively, by the presence of common carp; whereas yellow perch and northern pike relative abundance, size structure, condition, growth, mortality, and recruitment were unaffected.  Some zooplankton were more abundant in lakes with common carp while benthic invertebrate densities were generally lower in lakes with common carp.  A whole-lake biomanipulation experiment was conducted by renovating a lake with abundant common carp and comparing the physical, chemical, and invertebrate communities before (3 years) and after (3 years) the renovation, with the addition of a control lake without common carp.  Submergent vegetation and water clarity were greater after common carp removal.  Macroinvertebrate biomass generally increased following the removal of common carp.  These results indicate common carp can influence aquatic ecosystems by altering the physical habitat, invertebrate densities and ultimately sport fishes.