Limnological Changes in a Large Reservoir Following Vegetation Removal by Grass Carp

Abstract

ABSTRACT Grass carp (Ctenopharygodon idella) reduced the areal coverage of submersed macrophytes from 44% to 0% in a 8,100-hectare reservoir. This resulted in increased nutrient concentrations and abundance of all major phytoplankton divisions. During this seven-year study, conducted between 1979 and 1987, average annual chlorophyll a levels increased from 12–13 mg/m3 to 19–22 mg/m3. Water clarity declined, and this was attributable to higher algal biomass and not to increases in abiotic turbidity. Summer blue-green algal density and relative abundance to the phytoplankton increased over time coincident with macrophyte elimination. Densities of rotifers, cladocerans, and total zooplankton decreased approximately 1.5 years after macrophyte removal. This decline was likely due to increased abundance of planktivorous fishes.