Spatio-temporal variations in phytoplankton community structure in small water bodies within Lake Victoria basin, Kenya

Spatio-temporal variations of phytoplankton, expressed in terms of species composition and diversity collected at various sampling sites in small water bodies (SWBs) within Lake Victoria basin, Kenya, were investigated monthly from November 2010 to June 2011, in relation to selected physical and chemical water quality parameters. Temperature, D.O, TN and TP revealed a significant difference between the dams (p<0.005) unlike pH and BOD5. These SWBs were built during the pre-independence era and stocked with various species of fish. The dams provide water for both domestic and agricultural use. A total of 1392 phytoplankton species belonging to four families and 20 genera were identified in Kesses dam whereas in Kerita dam, a total of 376 phytoplankton species belonging to four families and 10 genera were identified. In Siaya dams, Yenga dam had three families of phytoplankton; Chlorophyceae, Euglenophyceae and Cyanophyceae with Mauna also recording four families: Chlorophyceae, Bacillariophyceae, Desmidiaceae and Cyanophyceae. All the SWBs generally registered low species diversity with majority of them recording a value of < 2. Seasonal variations in phytoplankton species composition and diversity were significant (P < 0.05) with low species composition and diversity occurring during the dry season, and being maximum following the end of the rainy season from November 2010 to March 2011, suggesting the possible influence of various environmental factors on the SWBs. Overall, water quality seemed to have had effect on the species diversity, dominance and richness of phytoplankton community structure.Key words: Community structure, small water bodies (SWBs), phytoplankton, species composition and diversity

Diversity, composition and abundance of macroinvertebrates associated with water hyacinth mats in Lake Victoria, Kenya

This study is set to investigate the macroinvertebrate community structure within water hyacinth in the Kenyan waters of Lake Victoria. This is helpful in determining the relationship between water hyacinth and macroinvertebrates. A total of four replicates were taken from 18 sampling stations within the lake using a Ponar grab and a 500 µm scoop net. The samples were washed through a 300 µm sieve and sorted alive in the field. The organisms were then identified to genus level and further categorized into functional feeding guilds using available keys and literature. The vertical position of the organisms at a water hyacinth mat was also examined. The data was then analyzed for diversity and abundance. One way ANOVA was further done to test any significant variation in community attributes between stations within the lake. All the physic-chemical parameters measured varied significantly though pairwise comparison revealed that most stations were in same sub set. A total of 14 orders and 34 genera were identified during the study. Out of which, 13 genera which include Chironomus, Lymneae, Hirudo, Tubifex, Platycnemis, Sympetrum, Trithemis, Melanoides, Biomphalaria, Ilybius, Elmis, Leptocerus, and Hexagenia were found at every sampling station. Most of the taxa found were predators probably feeding on mosquito larvae which could explain their absence. There was no significant difference in the diversity between stations though they varied in abundance. It is thus concluded that water hyacinth influences the distribution of macroinvertebrates and can thus be used to predict their presence. The feeding guilds were however assigned using existing literature. It is therefore recommended that a further study be done to confirm the feeding habits and the presence of mosquito larvae.Key words: Macroinvertebrates, hyacinth, Lake Victori