Brachionus falcatus and Platyias patulus indicating organic pollution in Ouémé River’s basin, Republic of Benin

Zooplankton is a biological compartment widely used in the bio-monitoring of aquatic ecosystems. It allows early detection of environmental disturbances even before reaching the upper compartments of interest to humans. The present study evaluated the ability of two rotifer species Brachionus falcatus and Platyias patulus to indicate organic pollution in the Ouémé River basin. Sampling was done between October 2014 and September 2015. Plankton net of 20 μm mesh size was used. Parameters such as NH4^+, NO2^- and PO4^3- were measured in water and used for the calculation of the Organic Pollution Index (IPO). The results showed that the occurrence of B. falcatus and P. patulus was 96.66% and 81.11%, respectively. Both species were particularly abundant in sites such as Kaboua and Vossa as well as downstream of the basin (Agonlin-lowé and Bonou). These strong abundances are linked to a very strong organic pollution in Kaboua and Vossa then to a high organic pollution at downstream. The least organically polluted station (Kpassa) had the lowest abundance of both species. B. falcatus and P. patulus are therefore two indicator species of organic pollution in the Ouémé River’s basin in Benin.