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

Abstract

Lake 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 lm; 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 (F 2,69 = 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 lg L )1 ), compared to the NG (119 ± 24 ind L )1 ; 53 ± 8 lg L )1 ) and SN sites (151 ± 26 ind L )1 ; 58 ± 9 lg 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 lg L )1 ) and nitrate-nitrogen (2121.7 ± 355.5 lg L )1 ) were much higher for the SL site, compared with the SN (8.2 ± 1.1 lg L )1 ; 28.6 ± 5.3 lg L )1 , respectively), and NG site (7.8 ± 0.8 lg L )1 ; 32.7 ± 5.4 lg 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.

Temporal patterns in phytoplankton, zooplankton and fish composition, abundance and biomass in Shirati Bay, Lake Victoria, Tanzania

“…The dominance of zooplankton species by cyclopoid copepods in Shirati Bay agrees with the results reported by Waya and Mwambungu (2004), Ngupula et al (2010), Vincent et al (2012) and Waya et al (2014), indicating cyclopoid copepods constitute the most dominant zooplankton group in Lake Victoria waters. The observed dominance of cyclopoid copepods is associated with their versatile feeding habits and efficient ability to escape from fish predators (Bradley et al 2012).…”

“…(), Vincent et al . () and Waya et al . (), indicating cyclopoid copepods constitute the most dominant zooplankton group in Lake Victoria waters.…”

“…Since 1990s, Lake Victoria has exhibited wide fluctuations in such abiotic factors as nutrient loading (Vincent et al . ). The lake has experienced extensive eutrophication manifested with the occurrence of low dissolved oxygen concentrations in deep water layers during the thermal stratification period (Hecky et al .…”

“…Biotic factors, in turn, include seasonal variations in food (phytoplankton) and top-down control by fish and other predators (Isumbisho et al 2006). Since 1990s, Lake Victoria has exhibited wide fluctuations in such abiotic factors as nutrient loading (Vincent et al 2012). The lake has experienced extensive eutrophication manifested with the occurrence of low dissolved oxygen concentrations in deep water layers during the thermal stratification period (Hecky et al 1994).…”

“…Previous studies focused on studying phytoplankton and zooplankton composition, abundance and biomass as separate groups, without considering their ecological interactions. Phytoplankton studies for Lake Victoria include those by Lung'ayia et al (2000), Machiwa et al (2005), Mbonde et al (2004), Sekadende et al (2005a), Ngupula et al (2011) and Sitoki et al (2012), while zooplankton studies have been conducted by Mavuti and Litterick (1991), Mwebaza-Ndawula (1994), Waya and Chande (2004), Waya and Mwambungu (2004), Ngupula et al (2010), Vincent et al (2012), Ngupula (2013) and Waya et al (2014). Despite the importance and interactions of phytoplankton with zooplankton in fisheries production, there is a paucity of information regarding their composition, abundance and biomass, and their relationship in the inshore waters of Lake Victoria, particularly in Shirati Bay.…”