Impact of Zooplankton Grazing on Phytoplankton Community Dynamics in Lake Nasser: An In-Depth Experimental Study of Predator-Prey Interactions

Hussian, Abd-Ellatif; Hegab, Mahmoud

doi:10.21608/ejabf.2025.446896

Impact of Zooplankton Grazing on Phytoplankton Community Dynamics in Lake Nasser: An In-Depth Experimental Study of Predator-Prey Interactions

Authors

10.21608/ejabf.2025.446896

Abstract

Through managed enclosure experiments conducted in Lake Nasser during autumn 2023, how zooplankton grazing rapidly reshapes phytoplankton communities was addressed. Four treatments were tested: a zooplankton-free control, natural zooplankton density (Treatment A), double density (Treatment B), and triple density (Treatment C). Across the 45 identified phytoplankton species, Cyanophyceae dominated (42% of total density), followed by Bacillariophyceae (31.5%) and Chlorophyceae (18.7%). Within 72 hours, intense grazing pressure in Treatment C reduced total phytoplankton density by 57%, from 2.8 × 10⁶ to 1.2 × 10⁶ cells/L. Zooplankton exhibited clear selective feeding, strongly targeting Bacillariophyceae—particularly Cyclotella glomerata, Synedra ulna, and Melosira granulata—as well as Chlorophyceae, while Cyanophyceae showed greater resistance to grazing. These findings highlight the pivotal role of zooplankton in structuring phytoplankton assemblages and underscore their potential as a biomanipulation tool for managing eutrophic lakes through targeted grazing control.

Keywords