The effect of fish stocking on mountain lake plankton communities identified using palaeobiological analyses of bottom sediment cores

Elwira Sienkiewicz,Michał Gąsiorowski

doi:10.1007/s10933-015-9870-2

Elwira Sienkiewicz, Michał Gąsiorowski

Open Access

https://doi.org/10.1007/s10933-015-9870-2

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Abstract

The artificial introduction of fish into a naturally fishless lake can effectively modify the food web and trophic status of that lake. We observed changes in the zooplankton community after stocking fish in Przedni Staw Polski, an oligotrophic mountain lake in the Tatra Mountains (Poland). Results were compared with observations about a stocked lake that naturally contained fish (Morskie Oko), and with two fishless lakes that served as reference sites. The main change observed in the cladoceran community of Przedni Staw Polski was the elimination of large-bodied Daphnia ~10 years after stocking fish. The introduction of fish also affected the phytoplankton community and resulted in an increase in diatom species related to higher trophic state, most likely due to the fish-induced alteration of the phosphorus cycle. Moreover, all of the studied lakes have been influenced by global and regional climatic and environmental changes, including intensive tourism and acid deposition. Changes in diatom communities were observed after fish stocking even in the lake with a natural fish population, while the zooplankton did not reflect higher fish density. These findings suggest that the natural balance between fish and phytoplankton was destroyed by fish stocking, and although it caused eutrophication in the lake, the higher fish density did not strongly modify the species composition of Cladocera.

Highlights

Fish are a very important element of the food web of a lake
Based on the Principal Component Analysis (PCA) trajectories of diatom and cladoceran sample scores, the most intense alterations occurred in the period of fish introductions
We observed a decline in large-bodied zooplankton immediately after fish stocking in a primary fishless lake and no significant change in a lake with a natural fish population

Summary

Introduction

Fish are a very important element of the food web of a lake. According to the top-down hypothesis, as top predators, fish can control the trophic state of a lake (Carpenter and Kitchell 1993). By selective predation on large-bodied zooplankton, planktivorous fish can effectively eliminate phytoplankton grazers and indirectly induce phytoplankton blooms. When fish are introduced to an oligotrophic, naturally fishless lake, it can quickly restructure the food web by effectively eliminating large-bodied cladocerans and copepods (Tiberti et al 2014). Fish stocking indirectly causes an increase in nutrient contents and algal biomass (Carpenter et al 1995). An increase in total phosphorus above 10 lg L-1 in the water of an oligotrophic lake leads to an alteration towards eutrophication. A higher nutrient load accumulates, which is available to phytoplankton and leads to increased algal production under conditions of reduced grazing by zooplankton (Schindler et al 2001; Wolfe et al 2003). Phosphorus release is controlled by many processes, which can be physical (e.g., resuspension, temperature), chemical (e.g., pH, redox state) or biological (e.g., bioturbation, submerged macrophytes) (Temporetti and Pedrozo 2000)

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