Ecological Approach of Plankton Responses to Water Quality Variables of a Tropical River, South-Eastern Nigeria: A Bio-indicator-based Community Assessment of Idundu River

In the present study, the water quality variables of the Idundu River were assessed by evaluating the Plankton community. Three sampling stations: Station 1 (minimal fishing), station 2 (artisanal fishing area/ cluster of human settlements) and station 3 (fisheries landing area, dredging) representing regions along the stretch of the watershed with considerable economic importance and anthropogenic activity, were selected within the period of six (6) months. The study determines plankton distribution, diversity and some water quality variables of Idundu River, and how they influence plankton abundance. The results of this study reveal that water quality variables (mean ± SD) of the River were pH (6.526 ± 0.104), surface water temperature (26.224 ± 0.106˚C), dissolved oxygen (1.474 ± 0.135 mg/l), nitrate (0.026 ± 0.001 mg/l) and phosphate (0.015 ± 0.000 mg/l). All the water quality variables assessed were within the acceptable range. A total of 23 phytoplankton species belonging to five families, totalling a numerical abundance of 368 individuals/L were observed. Bacillariophyceae was the most abundant phytoplankton family (63.81%), followed by Chlorophyceae (17.41%), Dinophyceae (7.87%), Cryptophyceae (9.77%), and the least abundant was Zygnemophyceae accounting for (1.08%). A total of 20 zooplankton species belonging to five phyla, totalling a numerical abundance of 140 individuals/L were observed. Rotifera was the most abundant zooplankton phylum (35.69%), Arthropoda (30.62%), Ciliophora (17.79%) and Annelida (12.15%); the least abundant was Nemata (2.85%). Principal component analysis (PCA) for plankton organisms showed that phytoplankton were more homogenously distributed than zooplankton during the study period. Shannon Wiener and Margalef’s diversity index showed that the River is in a healthy condition and the equitability level was high across all the stations, indicating even plankton distribution.