Phytoplankton species composition and abundance in a freshwater ecotone, Akwa Ibom State, South-Eastern Nigeria

Abstract

Phytoplankton composition and abundance could be used to evaluate the health of any aquatic ecosystem. Phytoplankton species were quantitatively sampled for twelve calendar months from Abak River, Nigeria using standard methods. Data generated were pooled and subjected to appropriate statistical analysis including descriptive and inferential statistics. The results showed that 3,901 cells/l, 45 species, 36 genera and 4 phytoplankton taxonomic groups were identified. The dominant species in terms of number of cells/l was Phormidium valderiae (1,770 cells/l; 45.37%) while the least (1 cell/l; 0.02%) were Closteriopsis longissima and Netrium digitus. Order of significance in terms of number of species was: Chlorophyta (20 species; 44.45 %) > Bacillariophyta (15 species; 33.33%) > Cyanophyta (9 species; 20.00%) > Xanthophyta (1 species; 2.22%). Dominance of the phytoplankton cell counts were observed in the following trend: Cyanophyta (65.27%) > Bacillariophyta (20.06%) > Chlorophyta (13.30%) > Xanthophyta (1.38%). Low abundance of this flora accompanied by the high occurrence of Cyanophyta cells and species are indications of pollution of this important aquatic ecosystem. Hence, wastes generation and dumping without pretreatments into the river especially, organic and inorganic fertilizers should be discouraged. Keywords: Phytoplankton group, abundance, species composition, cell counts