PRIMARY RESEARCH PAPER Ecological impacts of an exotic benthivorous fish, the common carp (Cyprinus carpio L.), on water quality, sedimentation, and submerged macrophyte biomass in wetland mesocosms Pascal H. J. Badiou • L. Gordon Goldsborough Received: 10 August 2014 / Revised: 5 February 2015 / Accepted: 9 February 2015 Ó Springer International Publishing Switzerland 2015 Abstract We examined the interactions of the common carp (Cyprinus carpio L.) and nutrient additions on water quality, sedimentation rates, and submerged macrophyte biomass in mesocosms in Delta Marsh, Manitoba, Canada. We wanted to determine if carp and nutrients interacted synergisti- cally to increase phytoplankton biomass. A two-by- three duplicated, factorial design had the following treatments: (1) control mesocosms with no carp or nutrient additions; (2) low carp density and no nutrient additions; (3) high carp density and no nutrient additions; (4) no carp and nutrient additions; (5) low carp density and nutrient additions; and (6) high carp density and nutrient additions. The presence of carp increased ammonia concentrations, turbidity, and phytoplankton biomass as expected but did not increase total reactive phosphorus concentrations. The presence of carp did not appear to interact synergistically with nutrient additions to increase phytoplankton as has been suggested by others. In mesocosms with high carp density and receiving nutrient enrichment, phytoplankton appeared to be suppressed relative to mesocosms receiving nutrient enrichment only, and nutrient enrichment and low carp density. Overall, the presence of carp appears to mimic the effects of eutrophication. Our results demonstrate that carp can cause a shift from a clear, macrophyte- dominated state to a turbid phytoplankton-dominated state at a biomass of less than 600 kg ha -1 . Keywords Common carp Á Eutrophication Á Wetlands Á Water quality Á Mesocosms Á Phytoplankton Á Suspended solids Á Turbidity Introduction Common carp (Cyprinus Carpio L.; hereafter ‘carp’) has a near-worldwide distribution and is one of the most introduced fish species (Badiou et al., 2011). Carp have been introduced to more than 100 countries, usually for aquaculture. Although carp can be valuable as a food and sport fish, it can cause numerous environmental changes when it invades and becomes established in freshwater ecosystems where it does not occur naturally. In particular, carp appears to reach a superabundance in regions of North America and Australia that are characterized by large spatially connected habitats and environmental instability Handling editor: Stuart Anthony Halse P. H. J. Badiou (&) Institute for Wetland and Waterfowl Research, Ducks Unlimited Canada, Box 1160, Stonewall, MB ROC 2ZO, Canada e-mail: p_badiou@ducks.ca L. G. Goldsborough Department of Biological Sciences, University of Manitoba, Winnipeg, MB R3T 2N2, Canada e-mail: gordon.goldsborough@umanitoba.ca 123 Hydrobiologia DOI 10.1007/s10750-015-2220-6