Analysis of the top-down and bottom-up effects on zooplankton biomass in eutrophic Lake Yeniçağa

Several aquatic ecological studies have focused on the contrasting effects of top-down and bottom-up interactions on zooplankton communities. It is essential to comprehend the relative strength of these interactions to evaluate the trophic interactions of pelagic food webs, an area that is still extensively researched due to its complexity. Therefore, we examined the biomass of zooplankton over a one-year period in a freshwater lake that is subject to multiple stressors such as anthropogenic activities, eutrophication. Top-down effects, namely fish biomass, and bottom-up effects, including total phosphorus, total nitrogen, and chlorophyll a concentrations were considered. Structural equation modelling (SEM) was employed to evaluate the relative impact of top-down and bottom-up effects on zooplankton. The SEM analysis revealed that zooplankton is influenced by both top-down and bottom-up effects in Lake Yeniçağa. The biomass of cladocerans was found to have a negative correlation with increasing chlorophyll a, while the Calanoida group was negatively affected by both fish biomass and chlorophyll a from top-down and bottom-up controls. The fish biomass had a positive effect on both Cyclopoida and Rotifera, but only Rotifera showed a negative interaction with chlorophyll a. Direct bottom-up effects of total phosphorus and total nitrogen on chlorophyll a were found, with total nitrogen having a stronger interaction than total phosphorus.