Relationships between fisheries, foodweb structure, and detrital pathway in a large shallow lake

We modeled energy transfer and trophic position of fish, plankton, and macroinvertebrates and the relative importance of top-down versus bottom-up processes in Lake Võrtsjärv, a large shallow eutrophic lake in Estonia (northeastern Europe). We employed input values based on 37 years of biomass and fishing activity monitoring for calibrating the Ecopath with Ecosim (EwE) model. Energy flows from primary producers and detritus, represented by total system throughput, were nearly equal (51 and 49%, respec- tively). Simulation revealed that top-down and bot- tom-up forces were at play, metazooplankton was not efficiently grazing phytoplankton production, and a trophic cascade proceeded through macroinverte- brates rather than through zooplankton. Detritivory was responsible for the relatively low trophic position of Võrtsjärv fish compared to other lakes. Bottom-up processes were the main drivers for the dual, primary production- and detritus-based pathways in energy flow. Our findings suggest that the predicted biomass increase of cyanobacteria in shallow lakes in the future will strengthen the reliance of consumers on the detrital pathway at the expense of the primary production pathway.This research was supported by the Start-Up Personal Research Grant PUT 777 to FC and UB, by IUT 21-2 of the Estonian Ministry of Education and Research, and by MARS project (Managing Aquatic ecosystems and water Resources under multiple Stress) funded under the 7th EU Framework Programme, Theme 6 (Environment including Climate Change), Contract No.: 603378 (http://www.mars-project.eu).This research was supported by the Start-Up Personal Research Grant PUT 777 to FC and UB, by IUT 21-2 of the Estonian Ministry of Education and Research, and by MARS project (Managing Aquatic ecosystems and water Resources under multiple Stress) funded under the 7th EU Framework Programme, Theme 6 (Environment including Climate Change), Contract No.: 603378 (http://www.mars-project.eu)