Stream invertebrates
In East Africa, stream invertebrates typically display a moderate biodiversity, squeezed as they are between semi-permanent high altitude running waters, which are naturally characterised by a moderate number of species, and lower reaches affected by high temperatures and pollution. Erosion caused by farming and cattle husbandry is responsible for the very high sediment yield that affects streams in Sub-Saharan Africa. In the Naivasha Basin these impacts are noticeable already at 2500 m a.s.l.
Common larvae of stream invertebrates include mayflies (Ephemeroptera) represented mainly by the families Baetidae, Caenidae and Heptageniidae, with other families, such as Leptophlebiidae and Oligoneuridae being relatively rare. Plecoptera are restricted to the single 'sibling species group' Neoperla spio (Perlidae), occasionally found in the Naivasha Basin; their occurrence does not seem to correlate with clean and well oxygenated mountain streams as is generally the case with Plectoptera in temperate regions.
Trichoptera are relatively diverse, the commonest belonging mainly to the net-spinning Hydropsychidae and Philopotamidae, and to the the case-making Leptoceridae, Lepidostomatidae and Goeridae. Other families such as the tube-making Polycentropodidae are less common. Pisuliidae, a small entirely afrotropical trichopteran family, is also occasionally reported.
Running water beetles (Coleoptera) are represented mainly by members of the Elmidae and Scirtidae families. Diptera larvae include chironomids and tipulids.
Research conducted on stream invertebrates in Kenya (Dobson et al. 2002, 2007; Masese et al. 2014) highlights a different role and composition of common invertebrate functional feeding groups than would be expected when using knowledge gathered from observations of stream invertebrates in temperate regions. The shredder guild, in particuar, tends to be dominated by freshwater crabs of the genus Potamonautes (Potamonautidae) and by tipulid larvae (Diptera). In the Naivasha basin, crabs are becoming progressively replaced by the Red Louisiana crayfish, introduced to the lake, which is expanding its distribution by towards higher river reaches.
