Analysis of the top-down and bottom-up controls on the zooplankton of eutrophic freshwater Yeniçağa Lake (Turkey)

Abstract

Abstract The objective of this study is to determine the relationship between zooplankton biomass and the factors that affect it and to assess the trophic status in Yeniçağa Lake, Turkey. For this purpose, chlorophyll-a values were used as the bottom-up effect, while planktivorous fish CPUE was used as the top-down effect. Additionally, to understand which nutrient has a stronger impact on chlorophyll-a, total nitrogen, and total phosphorus values were determined. Structural Equation Modeling was used to examine the bottom-up and top-down relationships, and it was understood that Cladocera, Calanoida, and Rotifera groups were negatively controlled by bottom-up effects, while Calanoida is negatively controlled and Cyclopoida and Rotifera are positively controlled by top-down effects. Moreover, it was understood that chlorophyll-a is influenced by both total nitrogen and total phosphorus, with a higher impact of total nitrogen. To determine the trophic status, chlorophyll-a, total phosphorus, Secchi depth, and Carlson TSI Indices obtained from these values were used. According to the findings from these values, the lake can be considered to be at the eutrophic level with a hypertrophic tendency.