Zooplankton Community Responses in a Perturbed Tropical Stream in the Niger Delta, Nigeria

ABSTRACT

The effect of abattoir wastes and other anthropogenic activities on the distribution and abundance of zooplankton and environmental variables were investigated in Orogodo River, southern Nigeria. Samples of zooplankton were collected 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 recovery 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 recorded 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 environmental 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 results indicate that the changing water quality status of the Orogodo River affected the zooplankton diversity and abundance and such measure could be used as a biomonitoring tool to determine the ecological health of the river.

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