Spatial and temporal distribution and diversity of zooplankton along a salinity gradient between the Lake Naivasha and the Lake Oloiden

There has been an increase in the water level in the Lake Naivasha (fresh water) which led to its merging with Lake Oloiden (saline). This was due to the increase in rainfall: associated with climate change. This may have an impact on the zooplankton community (biodiversity) due to the salinity gradient that resulted. A study was conducted to investigate the spatial and temporal distribution and diversity of zooplankton along a salinity gradient between the Lake Naivasha and the Lake Oloiden. The salinity was measured insitu using a YSI Multiparameter meter and zooplankton were sampled twice by towing a zooplankton net with a flow meter for 10 minutes (monthly, per site for one year). The zooplankton were identified and analyzed under a compound microscope (×100). The species diversity, evenness and species richness index were computed.  The salinity was higher in Oloiden ST1 and ST2 as compared to the rest of the sites while the correlation showed a slight positive association between salinity and zooplankton numbers. A total of 17 species were identified and they belonged to the following families: Branchionidae, Lecanidae, Trichocercidae, Sisidae, Daphnidae and Cyclopoidae. The density (Ind/l) was highest for daphnidae, cyclopoidae and sisidae; however, Lake Oloiden had a lower density as compared to the rest of the sites. The diversity index was low; H’= 0.87 for Oloiden ST2 and H’=0.64 for Crescent. Species richness (d) was highest (2.84) for Oloiden ST2 and lowest in Crescent (1.24). Species evenness was highest in Crescent (0.83) and lowest in Oseria (0.71). The diversity index, evenness and Margalef’s index was higher in Lake Oloiden as compared to Lake Naivasha. The salinity gradient had an impact on the distribution and diversity of zooplankton; species diversity, evenness and species richness increased with increase in salinity.