Spatial and temporal patterns in abundance and distribution of zooplankton in the Tanzanian waters of Lake Victoria

Abstract

Zooplankton composition and abundance, and its spatial and temporal distribution patterns were investigated from September 2005 to October 2007 at 51 sampling stations at various depths in the near shore, intermediate, and offshore waters of Lake Victoria. Relative to near shore (54.86 ± 32.33 ind. l−1) and far offshore (38.63 ± 11.14 ind. l−1), the intermediate waters (109.56 ± 64.70 ind. l−1) had highest abundance of zooplankton. A total of 43 zooplankton species were encountered: of those 26 species were rotifers, with Brachionus angularis, Brachionus calyciflorus, and Asplanchna sp. as the most abundant species. There were 9 species of cladocerans, with Diaphanosoma excisum and Bosmina longirostris as the most abundant species. There were 7 cyclopoid species with Thermocyclops emini, Tropocyclops tenellus, and Thermocyclops neglectus as the most abundant species. Only one calanoid species, Thermodiaptomus galeboides was encountered. Cyclopoid copepods were the most abundant (76.5%) followed by calanoids (11.3%), rotifers (8%) and cladocerans (4.3%). The present findings contrast with earlier studies from the 1930s and 50s, but agree with many thereafter. There is change of zooplankton composition and abundance with a trend towards small sized species instead of the large. Increased eutrophications, pollution, and predation pressure from an increasing abundance of dagaa, juvenile perches, and reappearing haplochromines, among others, are responsible for the observed spatial and temporal variability in distribution and abundance patterns, and generally, change.

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).…”

“…The dominance of zooplankton species by cyclopoid copepods in Shirati Bay agrees with the results reported by Waya and Mwambungu (), Ngupula et al . (), Vincent et al . () and Waya et al .…”

“…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.…”

Diet of Silver Cyprinid, Rastrineobola argentea in Lake Victoria, Kenya.

“…Results for the spatial diet composition differ from Owili (1999) who reported the dominance of cladoceran in the diet of R. argentea in the Nyanza gulf of Lake Victoria. The change in diet among stations could be attributed to the environmental effectscausing changes in zooplankton community (Ngupula et al, 2010). According to Wanink et al (2002) the zooplanktivore fish (i.e.…”

“…The fish therefore, has a crucial role in the ecosystem of Lake Victoria as a link between the zooplankton and the top predators (Manyala and Ojuok, 2007). The composition and abundance of zooplankton community in Lake Victoria has changed significantly following the deteriorating water quality caused by increased disturbances in its catchments (Ngupula et al, 2010). This is thought to have an impact on the feeding ecology of R. argenteain the lake since zooplankton forms its major food item.In regard tothis effect, the study aimed to determine the diet composition, ontogenic shift, spatial variation in diet composition, diel feeding and food selection ofR.…”