Zooplankton and environmental characteristics of Shiroro Lake at the extremes of its hydrological cycle

We studied the newly-created Shiroro lake, Nigeria, at the extremes of its hydrological cycle: high water level (HWL) and low water level (LWL). Temperatures reflected prevailing weather conditions; pH, dissolved oxygen, turbidity and suspended solids were highest during HWL, but transparency, conductivity, NO ₃ ^– -N, PO ₄ ^3– -P and Na⁺ were higher during LWL. A total of twenty-six species of pelagic zooplankton were identified: five species of cladocerans, eight species of copepods, and thirteen species of rotifers. The freshwater medusa (Limnocnida) and Daphnia longispina were absent during HWL but present at LWL, suggesting seasonality of the zooplankton community. Thermocyclops consimilis and T. emini are new records for Nigeria, bringing to nine the number of known Thermocyclops species in Nigeria.     

The effect of different algal densities of Scenedesmus acuminatus on the population growth of Moina micrura Kurz (Crustacea: Anomopoda,Moinidae)

Six densities (0.5 × 10⁶, 1.0 × 10⁶, 1.5 × 10⁶, 2.0 × 10⁶, 3.0 × 10⁶, and 4.0 × 10⁶ cells ml^–1) of the micro-alga Scenedesmus acuminatus, were fed to the cladoceran, Moina micrura, in 40-litre glass aquaria. Moina population increased with increasing cell densities of Scenedesmus only up to treatment 3 (i.e. 1.5 × 10⁶ cells ml^–1) where a peak population of 11303 individuals per litre was obtained. Moinapopulation growth was inhibited at higher algal densities. The percentage of egg-bearing females and the number of eggs per egg-bearing females, followed a similar pattern. Comparatively, the peak production density of approximately 11000 Moina per litre, is interesting from a mass production point of view and indicates that S. acuminatus is a satisfactory micro-alga food for M. micrura.