Abstract

Benthic Macroinvertebrates in Kenyan waters of Lake Victoria were sampled on a monthly basis from March 1994 to March 1995. Sampling was carried in 10 stations representing all the six major ecological zones/habitats. Concurrently, water parameters dissolved O2, pH, temperature, conductivity, turbidity and transparency were measured at the same site as the benthos. In addition, water samples for analysis of alkalinity, hardness, nutrients (NO3, NO2, PO4), Silica, heavy metals (Fe, Pb, Cu, Mn, Zn, Cd, Cr), were collected. Sediment were also sampled for heavy metal analysis and organic content.
  Deep-water stations (zone VI, > 12 m) were characterized by very low species richness and abundance. Only three species Branchiura sowerbyi Beddard (Oligochaeta), Chironomus formasipennis (Diptera) Sphaerium nyanzae Smith (Mollusca) were recorded in deep waters. Stations in shallow waters (< 3.5 m) near river mouths in zones I and V were characterized by very low species richness and extremely high abundance of one or two species. The Oligochaete family Tubificidae dominated in abundance in these two zones. Other species were the mollusc Sphaerium nyanzae Smith and the swamp worm Alma emini. Michaelsen. In the other stations, molluscs Melanoides tuberculata Muller and Bellamya unicolor Olivier dominated in abundance. Other species were larvae and nymph of insects belonging to the orders/families Chironomidae, Ephemeroptera, and Trichoptera. The dominant species were Povilla adusta Navas, Caenis spp. and Libellula spp. (Odonata).
  Multivariate analysis using CANACO showed that in deep waters (zone VI) benthos species composition and abundance was mainly influenced by oxygen. On the other hand, industrial effluents from agriculture-based industries in the catchment were the determinant of benthos distribution in shallow waters near river mouths in zones I and V.