Experimental Evaluation of Food Chain Manipulation as a Means for PreventingAlgal Blooms in Lakes

摘要

The study investigated means of manipulating lake food chains to enhance grazingby zooplankton and thereby to decrease algal biomass and to improve water clarity. Experiments were conducted at two levels. The authors monitored a relatively deep, stratified lake for two years prior and one year following the removal of fish by treatment with rotenone and they manipulated zooplankton, fish, and nutrients in two series of experiments in 7000 liter mesocosms. Fish removal resulted in a shift in the zooplankton community to larger species, a substantial improvement in water clarity, and a decline in algal biomass. Mesocosm experiments showed that zooplankton communities dominated by moderate-sized native zooplankton or by introduced Daphnia pulicaria were equally effective in preventing algal blooms under both ambient and highly enriched nutrient levels when fish were absent. Introduced D. pulicaria out competed native zooplankton, suggesting that the association of large Daphnia with low algal biomass is due to competition.