ZOOPLANKTON PERIODICITY AND ENVIRONMENTAL VARIABLES IN SHIRORO LAKE, NIGERIA

Abstract

Zooplankton dynamics and periodicity in a water body provide useful information on the ecological status of the water body and may serve as bio-monitors of ecosystem health. In this study, we investigated the monthly variation of zooplankton community structure and the environmental variables of Shiroro Lake in north central, Nigeria between January 2013 and December 2015 using standard methods with the aim of ascertaining the ecological status and ecosystem health of this lake. Results obtained indicated that most of the physicochemical parameters examined showed variations within the months as affected by the rainfall regime. Temperature fluctuated between 20.8 and 27.4oC, pH (7.19 – 8.04), transparency (17.8 – 23.73cm), dissolved oxygen, DO (3.34 – 8.04 mg/l), BOD (2.34-3.33mg/l), total hardness (25.57 – 36.43mg/l), alkalinity (13.45 – 15.72 mg/l), phosphate (0.22 – 0.32 mg/l), magnesium (0.26 - 0.35mg/l), nitrate (0.29 – 0.61mg/l) and total dissolved solids (90.5 – 154.5mg/l). Diversity was rather low with only 19 genera recovered from the water body consisting of 5 Rotifers, 6 Cladocera and 8 Copepods. Generally, abundance was significantly higher in the dry season (November – April) as compared with the wet season period (May – October). Although, the cladocerans (Moina and Diaphanosum) had significantly higher abundance values, Keratella (Rotifer), and Ceriodaphnia (Cladocera) were the dominant taxa occurring in all the months. Furthermore, the zooplankton population fluctuated well with the temporal changes in environmental variables with DO and nutrients (phosphate and nitrate) accounting for most of the variations observed by Canonical Correspondence Analysis (CCA). The Shiroro Lake is a stressed water body owing to the numerous human activities occurring there. Care should therefore be taken to protect and preserve the fauna species by ameliorating the effects of the pollution.