Impact of three-spined sticklebackGasterosteus aculeatuson zooplankton and chlain shallow, eutrophic, brackish lakes

The 3-spined sticklebackGasterosteus aculeatusoften dominates fish communities in eutrophic, brackish, north-temperate lakes where it is thought to contribute significantly to the low zooplankton biomass and low grazing pressure on phytoplankton. To elucidate its effect on zooplankton community structure and phytoplankton biomass (chla), we conducted a 5.5 mo enclosure experiment with sticklebacks at different densities in high nutrient concentrations and a salinity of 2 psu. Increasing fish density (0 to 10.2 sticklebacks m–2) led to substantial changes in the zooplankton community structure, an increase in phytoplankton chla, and a reduction in water clarity. At densities below 4 to 6 sticklebacks m–2, large-bodied cladocerans dominated the zooplankton biomass, the zooplankton: phytoplankton biomass ratio was high (>1), and chlawas accordingly low (