Variations in zooplankton community structure and water quality conditions in three habitat types in northern Lake Victoria

Abstract

AbstractLake Victoria is vulnerable to increasing eutrophication, which has become manifested in ecological changes not yet fully understood. From October 2009 to January 2010, the influence of water quality on zooplankton community structure in three habitats in northern Lake Victoria, including sewage lagoons at the lake shores, Napoleon Gulf (NG) and the interface between the lake and the Nile River (also known as Source of the Nile River), was examined. Selected physico‐chemical parameters (dissolved oxygen concentration; water temperature; electrical conductivity; water depth) were measured in‐situ, while water samples were collected for chlorophyll‐a determinations. Zooplankton was sampled with conical plankton net (mesh size 60 μm; 0.25‐m mouth diameter). The NG and Source of the River Nile (SN) sampling sites exhibited significantly higher species richness, relative to the Sewage Lagoons (SL) site (F2,69 = 68.533; P < 0.05). Higher mean densities and dry biomass of zooplankton was generally a characteristic of the SL site (8715 ± 3241 ind L−1; 1862 ± 451 μg L−1), compared to the NG (119 ± 24 ind L−1; 53 ± 8 μg L−1) and SN sites (151 ± 26 ind L−1; 58 ± 9 μg L−1). Copepoda constituted a high numerical composition of the zooplankton at the NG and SN sites (>90% for both sites), while Rotifera dominated the zooplankton community at the SL site (97%). The mean values (±SE) of soluble reactive phosphorus (4060.7 ± 776.6 μg L−1) and nitrate–nitrogen (2121.7 ± 355.5 μg L−1) were much higher for the SL site, compared with the SN (8.2 ± 1.1 μg L−1; 28.6 ± 5.3 μg L−1, respectively), and NG site (7.8 ± 0.8 μg L−1; 32.7 ± 5.4 μg L−1, respectively). This study indicated the nutrient‐rich conditions observed at the SL site suppress the zooplankton species diversity, but favour species‐specific abundance and biomass. These study results indicate the zooplankton community structure can be used as a biological indicator of water quality in the Lake Victoria region.