THE CRUSTACEAN ZOOPLANKTON ASSEMBLAGE OF A RELATIVELY PRISTINE UTOR RIVER IN SOUTHERN NIGERIA

Abstract

The water quality and crustacean zooplankton of Utor River, a relatively pristine freshwater body in Edo State, Nigeria was investigated at four stations. The Utor River is slightly acidic, well oxygenated, oligotrophic and low in solids, conductivity, cations and heavy metals. A total of 380 individuals comprising eleven taxa were recorded, and the highest density was observed at Station 1 (29.9%) followed by Stations 2 (25.0%), while Stations 3 and 4 accounted for 24.2% and 21.1% respectively. Overall density showed no significant difference (P> 0.05). Copepoda represented by the family Cyclopoidae contributed 57.89% of the total density. The dominant species were Cryptocyclops bicolor, Ectocyclops phaleratus and Mesocyclops ogunnus. The Harpacticoida (15% of the population) was represented by one taxon Bryocamptus birsteini which was well represented in all the stations. The water quality assessment shows that the river is still relatively pristine and unperturbed. The crustacean zooplankton assemblage was cosmopolitan and dominated by the Copepoda in terms of the number of species and overall abundance, with Crypptocyclops bicolor as the most important species. The overall abundance and diversity of zooplankton was relatively low