A survey of phytoplankton and zooplankton communities in the newly created Tugwi-Mukosi reservoir, Zimbabwe, during the filling phase

Abstract

The plankton assemblages of Tugwi-Mukosi reservoir in south-eastern Zimbabwe were assessed seven months after impoundment to form a baseline for future monitoring and tracking of changes linked to the reservoir’s ontogenetic development processes. While cyanobacteria were the dominant group at all sites (50−70%), relative abundances of Bacillariophyceae and Chlorophyceae was considerable. The most abundant phytoplankton species were Microcystis aeruginosa and Aulacoseira granulata, whose abundances ranged from 3 200−28 800 ind. l−1 and 1 640−3 146 ind. l−1, respectively. Phytoplankton species richness in the reservoir ranged from 9 to 20, with the highest species richness in the north-eastern region of the reservoir. Zooplankton density was <1 ind. l−1 and after seven months since impoundment, the zooplankton community had not fully established. Twenty zooplankton species comprising of Rotifera, Copepoda and Cladocera were recorded. Cladocera, mainly Diaphanosoma excisum and Ceriodaphnia cornuta, were the most abundant followed by copepods, mainly Thermoclops sp. and Eodiaptomus japonicas. The dominance of Microcystis aeruginosa presents potential future challenges to water quality management, because increased nutrient loading can favour it, resulting in similar challenges being experienced in Lake Chivero. The establishment of an Integrated Lake Basin Management is strongly recommended to avert this.