Zooplankton assemblage of a tropical rainforest river in Nigeria

The community structure of zooplankton of Osse River at Ifon in Ondo State (Nigeria) was investigated at four sites between February and July 2009. Among the physical and chemical parameters studied, flow rate was significantly higher (P < 0.001) in station 2 than other stations which were not significantly different (P > 0.05) from each other. The study revealed the occurrence of 26 species of zooplankton, comprising 9 species of Rotifera, 12 species of Cladocera and 5 species of Copepoda. Rotifera accounted for 55.46% of the total number of organisms encountered, while Cladocera and Copepoda contributed 30.25% and 14.29% respectively. Lecanidae was the dominant family of rotifers, while the Sididae and Cyclopidae were the most dominant cladocerans and copepods recorded. The overall abundance of zooplankton was significantly different (P < 0.05) among the study stations. A posteriori Duncan Multiple range (DMR) test showed that the abundance was significantly higher (P < 0.05) in 2 stations. Diversity indices comprising Margalef index, Shannon-Wiener and Evenness indices were highest in station 3. The impact of cultural eutrophication on the abundance and diversity of zooplankton is reported.Keywords: Zooplankton, Community structure, Abundance, Distribution, Freshwater, Tropical River