How Does Increased Eutrophication and Pollution in the Lake Victoria Waters Impacts Zooplankton?

Abstract

To understand how eutrophication and pollution impacts zooplankton in the Lake Victoria waters, zooplankton samples were collected during a 21 days survey conducted from 6^th to 27^th May, 2013 constituting a total of 71 sampling stations. A net of 60 μm nitex mesh was used for the purpose. The lake waters were categorized into six ecological zones with the understanding that, inshore waters are the most highly impacted as compared to nearby and far offshore. Comparing to the data collected in 2007, it can be concluded that zooplankton have decreased in abundance. The inshore waters indicated the highest abundance contrasting the far offshore. Cyclopoids dominated other zooplankton by 73% and were evenly distributed in all the waters while calanoids (18%) increased towards offshore locations. Rotifers were the least in abundance (4%), after cladocerans (5%) and were confined in the inshore waters. In regards to the fact that calanoids and cladocerans dominated the Victoria waters during 1930s and the fact that predation forces from zooplantivores fish (like Rastrineobola argentea Pellegrin 1904 (dagaa), haplochromines, and juveniles of Nile perch (Lates niloticus, L.)) are not responsible for the reversed situation, then the findings imply that increased eutrophication and pollution impacts the lake zooplankton by favouring the increase of cyclopoids and some species of rotifers while limiting the calanoids and cladocerans to mainly offshore locations. The current observed low abundance of zooplankton does not threaten the pelagic fishery of the lake.