Composition and structure of phytoplankton community in Ouémé River basin, Republic of Benin

This study aimed to assess the composition and structure of floating phytoplankton assemblage in Ouémé basin. Phytoplankton samples were collected monthly from October 2014 to September 2015. Quantitative samples were taken with a horizontal Van-Dorn sampler and 20 μm mesh plankton net was used for additional qualitative sampling. Microscopic observation of phytoplankton allowed identification of 208 species including 70 Bacillariophyta species, 58 Chlorophyta species, 24 Charophyta species, 21 Euglenophyta species, 18 Cyanophytes species, 9 Phyrrophyta species, 5 Ochrophyta species and 3 Cryptophyta species. The Shannon diversity index varied from 2.4 bit.ind^-1 and 3.1 bit.ind^-1 showing a relatively good diversification of the community. The population appears largely dominated by 14 species which represent 83.8% of the total phytoplankton. Aulacoseira granulata and Euglena gracilis were the most predominant species with respectively 40.17% and 15.91% relative abundance. Regarding the horizontal pattern of phytoplankton abundance, downstream stations have the greatest abundances. So, the results suggest that downstream stations are richer in phytoplankton which structure differs from that in upper stations.