Zooplankton associations and environmental factors in Ogunpa and Ona rivers, Nigeria.

Zooplankton abundance, composition and environmental parameters were monitored in two tropical rivers over a twenty month period. The data was subjected to cluster, factor and correlation analysis to determine the grouping pattern of zooplankton and their relationship to environmental parameters. Environmental factors in Ogunpa and Ona rivers--included buffering capacity, trace metal ions, pH-temperature/transparency--were primarily influenced by rainfall. The dominance of the Rotifera in both rivers was attributed to their short developmental rate and fish predation on larger zooplankton. Two groups of associations were identified in each river--a commonly occurring species group exhibiting strong homogenous correlation with environmental factors and a predominant group exhibiting weak correlation with environmental factors and whose abundance/composition may be defined by biotic factors.