Seasonal distribution of phytoplankton in the Aby lagoon system, Ivory Coast, West Africa

Abstract

Seasonal variability of phytoplankton species composition, abundance and physical and chemical factors influencing phytoplankton dynamics were investigated in the Aby lagoon system, south-eastern Ivory Coast, covering the  main climatic seasons in 2006–2007. Seasonal and spatial variability of nutrient concentrations in the system were influenced by freshwater inflow from the Bia  and Tanoé rivers. The decrease in the salinity gradient in Aby Lagoon, which is  permanently stratified during the long dry season, increased the bottom inputs of soluble reactive phosphate and soluble reactive silicate which, in combination  with good light penetration during the long dry season, enhanced phytoplankton  production in the system. During the rainy seasons, water discharges into the system washed phytoplankton biomass out, preventing the development of  blooms. Overall, 192 taxa from eight phyla were recorded: Bacillariophyta  (32%), Chlorophyta (31%), Cyanobacteria (23%), Euglenophyta (12%), Dinophyta (0.5%), Xanthophyta (0.5%), Chrysophyta (0.5%) and Rhodophyta (0.5%). During the long dry season, Cyanobacteria cells comprised >50% of the phytoplankton abundance. The main phytoplankton taxa responsible for this high abundance were Microcystis aeruginosa, Oscillatoria princeps, Pseudanabaena limnetica, Aphanizomenon sp. 2 and Anabaena planctonica.

Keywords: abundance, choked lagoon, community distribution, diversity, environmental variables, river inputs

African Journal of Aquatic Science 2011, 36(3): 321–330