Etude Préliminaire de la Diversité et de la Structure du Peuplement Zooplanctonique de la Rivière Okpara au Bénin

Abstract

The objective of this study was to assess the diversity and structure of zooplankton in the Okpara River. The river's zooplankton were identified and their community structure assessed at nine selected stations using taxonomic richness, density, the Shannon diversity index and the Pielou equitability index. A total of 68 species of zooplankton were recorded, divided into three groups: rotifers (57), copepods (07) and cladocerans (04). The number of species was higher in the lower reaches than in the upper and middle reaches. Rotifers were the most abundant group with 78.25% of the total abundance, followed by copepods (20.7%) and cladocerans (1.3%). Keratella valga and Tropocyclops confinis were the most abundant species. Mytilina sp., Asplanchna girodi, Anuraeopsis sp., Lepadella sp., Asplanchna brightwellii, Asplanchna navicular, Trichocerca sp. and Trichocerca tenuior were recorded at all stations. The values for abundance and density of zooplankton are higher in the dry season than in the rainy season. The values for species richness, Shannon diversity index and Pielou equitability are higher in the wet season than in the dry season. The strong presence of certain pollution indicator species such as Asplanchna brightwelli, Brachionus angularis and Brachionus falcatus could indicate the presence of organic pollutants in the river. Effective monitoring measures therefore need to be put in place to protect the river from anthropogenic intrusion.