Zooplankton communities in Lake Nasser, Egypt, under the current flood regime, before the construction of Grand Ethiopian Renaissance Dam (GERD)

Abstract

This study focuses on changes in zooplankton composition and abundance in Lake Nasser during different flood periods before the construction of the Grand Ethiopian Renaissance Dam (GERD). Field surveys were carried out in August 2016 (flood period), December 2016 (post-flood period), and May 2017 (pre-flood period). Fifteen sampling sites representing five sectors were selected to cover the lake whole area. The results revealed a highly significant difference (p ≤ 0.016) in the density of all identified zooplankton groups among different flood seasons and lake locations. The zooplankton standing crop during the flood was higher, by a factor of approximately 3.7, than that recorded in post-flood and pre-flood periods. Zooplankton was dominated by medium-sized Copepoda, two cyclopoids (Thermocyclops neglectus and Mesocyclops ogunnus) and one calanoid (Thermodiaptomus galebi). The euplanktonic rotifer Keratella cochlearis dominated, during post-flood and pre-flood periods, constituting approximately 83% and 77% of total rotifer densities, respectively. Keratella tropica occurred in greatest density during flood made up 52.6% of total rotifers. Diaphanosoma mongolianum was the main cladoceran during flood and post-flood periods, whereas Ceriodaphnia dubia densities were highest for pre-flood periods. This study found that flood regime affect zooplankton composition and density in Lake Nasser.