PLANKTON AND PRIMARY PRODUCTIVITY OF LAKE MANZALA, EGYPT

Primary production and distribution and abundance of phyto- and zooplankton of lake Manzala were investigated from June 1985 to June 1986. Primary production varied from 4.1 to 28.7 g O2 m-2 d-1 with the highest values 24.2 and 28.7 g O2 m-2 d-1 recorded in the eastern and southern sectors and the lowest value 4.1 g O2 m-2 d-1 recorded in the northern sector. The seasonal mean production for the lake was estimated at 13.3 g O2 m-2 d-1. Mean phytoplankton abundance ranged from 32.7 107 to 76.1 107 cells m-3 with a mean value of 48.107 cells m-3. Diatoms were the dominant phytoplankton group comprising 52 to 90 % by number. The greatest relative abundance (87 to 90%) was recorded in the southern sector. Mean zooplankton abundance ranged from 30.1 103 to 44.4 103 organisms m-3 in the eastern sector to 5.5.103 in the northern sector. In response of eutrophication, the species composition changed significantly over the last 20 years. Cladocerans represented less than 1% of zooplankton during 1959/60, but 75% in 1985/86. Rotifers constituted 40% in 1959/60, and only 1% in 1985/86. Cirriped larvae declined from 21% to 1%. © 1990 Kluwer Academic Publishers.