SPATIO-TEMPORAL DISTRIBUTION OF CRUSTACEANS IN A SHALLOW LAKE, LAKE ZIWAY

Abstract

Abstract This study presents spatio-temporal variations of crustacean community in relation to turbidity and predation in one of the Ethiopian Rift Valley lakes, Lake Ziway, based upon one year biweekly sampling data. Abundance of cladocerans correlated best with secchi depth (P<0.0001) and weakly and negatively with Chlorophyll a (p=0.0067). Copepods responded to Chlorophyll positively (p=0.0003) but not to secchi depth. Three major peaks in total crustacean biomass were recorded inshore but a single maximum (less than half of the inshore value) offshore. Abundance and biomass were highest inshore, where a macrophyte belt along the shore of the lake provides shelter and enables the crustaceans to avoid predation. Mean annual biomass of zooplankton was 82.5 mg m -3 . Dominant crustaceans: Moinamicrura, Thermocyclopsdecipiens and Mesocyclopsaequatorialis, contributed 90.8 % of the total annual zooplankton biomass. Temporal variation in crustacean biomass was associated with water transparency. Minimum total cladoceran biomass was recorded during the wet season. On the other hand predation by catfish and Chaoborus on larger sized copepods leads them to show diel migration in such a turbid shallow lake and to a shift in zooplankton community structure where small sized Thermocyclops and pre-adult copepods were dominant throughout the sampling period.