Abstract
Primary productivity and distribution and abundance of phyto-and zooplankton of lake Manzala were investigated from June 1985 to June 1986. Primary productivity varied from 4.1 to 28.7 g O2/sq m/day with the highest values 24.2 and 28.7 g O2/sq m/day recorded in the eastern and southern sectors, respectively, and the lowest value 4.1 g O2/sq m/day recorded in the northern sector. The seasonal mean production for the lake was estimated at 13.3 g O2/sq m/day. Mean phytoplankton abundance ranged from 327 million to 761 million cells/cu m with a mean value of 481 million cells/cu m. 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 30,100 to 44,400 organisms/cu m in the eastern sector to 5,500 in the northern sector. In response to eutrophication, the species composition changed significantly over the last 20 yr. Cladocerans represented < 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%. (See also W90-11859) (Author 's abstract)