Vertical distribution of zooplankton in Lake Nasser

Abstract

The composition and distribution of zooplankton communities in three depths (surface, 10-5m and 20-15m depths) along main channel of Lake Nasser were studied in 2013. The density of total zooplankton was increased to maximum during winter and autumn at surface water (39,362 and 63,100Ind.m -3, respectively) and gradually decreased with depth until attaining the lowest average density at 20-15m (12,460 and 8976Ind.m -3). During spring and summer, zooplankton was irregularly distributed through the water profile, where the highest average density was recorded at 10-5m depth (66,007 and 66,734Ind.m -3). Copepoda was the dominant zooplankton group at all depths, it represented about 70-76.2% of the total zooplankton count. Cladocera formed about 13.4%, 14.5% and 11% of total zooplankton density for surface, 10-5m and 20-15m depth. It was decreased with increasing depth during winter and autumn; however it attained its maximum density at 10-5m depth during spring and summer. Rotifera average density decreased with increasing depth. The dominant zooplankton species inhabiting Lake Nasser were strongly temperature-dependent. The study recommends the introduction of some pelagic fish species to consume the high persistence of zooplankton community at the upper 10meters of water column.