Zooplankton Community Responses in a Perturbed Tropical Stream in the Niger Delta, Nigeria~!2009-07-22~!2009-10-22~!2010-04-09~!

Abstract

The effect of abattoir wastes and other anthropogenic activities on the distribution and abundance of zooplank- ton and environmental variables were investigated in Orogodo River, southern Nigeria. Samples of zooplankton were col- lected for a period of six months from three stations, representing upstream of the river course, effluent discharge point and downstream of the river course. A combined total of 79 species of zooplankton were encountered in the study. Station 1 recorded the highest number (78 species), station 2 with 22 taxa and station 3 with 72 representative taxa, showing re- covery in terms of diversity and abundance of zooplankton. Rotifers of the order Bdelloidea dominated all the stations and were relatively high in station 2 indicating their tolerance to a wide range of impact. Generally, the cladocerans were abundant at all stations. However, Moina micrura, and Thermocylops neglectus were the only members of this group re- corded in station 2. The low fauna diversity experienced in station 2 throughout the period of sampling showed strong evidence of impact arising from the abattoir waste discharge and heavy human activities at that station. Local environ- mental conditions (i.e. Temperature, flow velocity, depth, dissolved oxygen, alkalinity and conductivity) accounted for 69% of variation in zooplankton assemblages using canonical correspondence analysis (CCA). Seasonal trends in zooplankton community composition were also related to changes in environmental characteristics of the river. Our re- sults indicate that the changing water quality status of the Orogodo River affected the zooplankton diversity and abun- dance and such measure could be used as a biomonitoring tool to determine the ecological health of the river.