The role of body size in the impact of common carpCyprinus carpioon water quality, zooplankton, and macrobenthos in ponds

Abstract

Common carp, a fish species blamed for profound adverse impacts on invaded freshwater ecosystems, can reach a large body size. We investigated the effects of carp size on water quality and on abundance of submerged macrophytes, zooplankton, and benthic macroinvertebrates in drainable ponds. Each pond was stocked with one of three age-classes of carp (young-of-the-year, 1-year-, and 2-year-old fish) corresponding to specific size ranges (classified as small, medium, and large carp). Water turbidity and chlorophyll a concentrations increased over time in the presence of all sizes of carp; ponds containing medium-sized fish tended to be most turbid. Submerged macrophyte biomass was not significantly affected by fish size. Neither total zooplankton nor macrobenthos biomass differed between ponds stocked with different-sized carp, but fish size was significant in determining the size composition of these communities. Copepods and small-bodied cladocerans were least abundant in the presence of small carp, while large cladoceran grazers were most suppressed in ponds with medium-sized fish. Among dipterans (primarily chironomids), which dominated the macrobenthos, densities of small larvae did not differ across fish sizes, while large larvae were more abundant in ponds stocked with small carp than in those with larger fish. Our results highlight the importance of fish body size in structuring aquatic communities, although the effects need not be linearly related to fish size. We caution against considering the effects of omnivorous fish on lower trophic levels to be unstructured and extrapolating the experimental results from one size range (developmental stage) to others.