Comparison of the impact of native (Scardinius erythrophthalmus) and invasive (Carassius auratus gibelio) omnivorous fish on plankton and bethic algae communities, water quality and submerged macrophytes

Abstract Shallow lakes are often rich in submerged macrophytes that play an important role in functioning of shallow lake ecosystems. Omnivorous fish can intensify eutrophication by enhancing the growth of phytoplankton, leading to higher water turbidity and light attenuation with negative effect on the growth of submerged macrophytes. However, the effects of different omnivorous fish species on aquatic ecosystem are not necessarily the same. A 70-day outdoor experiment was conducted in mesocosms containing meadow-forming arrowhead (Sagittaria sagittifolia) and canopy-forming clasping leaf pondweed (Potamogeton perfoliatus) to test the hypothesis that different species of omnivorous fish, the native species Rudd (Scardinius erythrophthalmus) and invasive Prussian carp (Carassius auratus gibelio) have different effects on plankton and benthic algae communities, water quality and submerged macrophytes growth. Both fish species increased the phytoplankton biomass and the concentrations of total and inorganic suspended solids and decreased water transparency and Prussian carp had a stronger effect than Rudd. The fish also changed the phytoplankton composition decreased the densities of zooplankton, except rotifers with more pronounced impact by the Prussian carp. Rudd decreased the dry weight of the above-ground part of arrowhead and of pondweed roots, while Prussian carp decreased the biomass of the whole pondweed. Canonical analyses showed that impact of all studied factors on pondweed growth was 2.6 times greater in Prussian carp than in Rudd treatments. Our findings thus showed differential effects of the two omnivorous fish species on plankton communities, water quality and submerged macrophytes, with Prussian carp having more pronounced impact than Rudd.