Abundance and Diversity of Zooplankton in the Lower Reach of the Opobo River, Rivers State Nigeria

Abstract:

Zooplankton are diverse group of organisms with little or no swimming ability. They are the animal component of plankton, have short life cycle and quickly respond to changes in their environment; hence, their abundance and community structure serve as an essential tool in providing information on the water quality of a given aquatic environment which may serve as an indicator of the ecological status of the water body. The aim of this study is to determine the abundance and diversity of zooplankton in the lower reach of the Opobo river. In this study, 6 stations namely Opu-Kala-Ama (ST 1), Uta-Ewa (ST 2), Ascon Jetty (ST 3), Opobo Town (ST 4), Queens Town (ST 5) and Down-Below (ST 6) were chosen along the river. Zooplankton samples were collected monthly by towing a plankton net of 35 µm mesh size and 0.196m2 mouth surface area from a motorized boat and preserved in 4% formalin. Sampling was for a period of 6 month (March- August 2008). Identification and counting of zooplankton were done with a compound microscope of 10x10 magnifications. Data was analysed using XLSTAT and JMP statistic package. Comparing of means and multivariate analysis was done using ANOVA and PCA (Principle Component Analysis) respectively. A total abundance of 30,368 zooplankton measured in cell/ml was recorded. The diversity structure comprised of 12 Zooplankton species belonging to 9 families (Copepoda 82%, Decapoda 3%, Gastropoda 4%, Bivalve 3%, Echinodermata 2%, Spirotricha 2% Polychaete 1%, Rotifera 3% and Cladocera 0.1%). Acartia longiremis showed high dominance in nearly all the stations exception of Opu Kala-Ama which was dominated by Calamus finmarchicus. Zooplankton diversity indices showed a fairly high Shanon diversity index only in ST4 (2.05) and low Margalef diversity index in all the stations. The findings of this work revealed that the Opobo river has high zooplankton abundance with low diversity.