RESPONSES TO FOOD-WEB MANIPULATION IN A SHALLOW WATERFOWL LAKE

We evaluated effects of fish removal from a large, shallow lake that historically was an important feeding area for migrating diving ducks. In the decade before fish removal, turbidity was high, submerged macrophytes and benthic macroinvertebrates were not abundant, and waterfowl use was negligible. Zooplankton and benthic macroinvertebrates increased during the first three post-treatment years. Water clarity improved initially in response to cladoceran grazing, allowing expansion of submerged macrophytes. Subsequent increases in water transparency may have been related to decreased sediment resuspension and lower algal biomass owing to allelopathic inhibition or nutrient competition from submerged macrophytes. Use by migrating diving ducks increased dramatically, apparently owing to changes in macroinvertebrate and plant foods.