Phytoplankton Composition and trophic state of Guessabo lake (Upstream in Buyo lake, Ivory Coast)

Abstract

Objectives: The trophic quality of Guessabo Lake (Ivory Coast) under the influence of fishing and agriculture was analysed starting according from the phytoplankton composition. Methodology and results: Sampling spatio-temporal in pelagic zone were made from a plankton net and supplemented with an integrated sampler. A total of three hundred and forty six species were identified. The groups, by orders of prevalence are, Chlorophyta with 164 species (48 %), Euglenophyta with 64 species (19 %), Cyanobacteria represented by 53 species (16 %), Bacillariophyta with 50 species (15 %) and, the other groups (Pyrrophyta, Chrysophyta and Xanthophyta) represented by 15 species (4 %). On the level of sampling stations of Guessabo Lake, 239 species were identified in Guemon sector against 231 and 257 species respectively in bed of the lake and Haut Sassandra sector. Concerning Guemon sector, 181 species were recorded at station G1 and 192 at station G5. In bed of lake (Channel), 154 species were listed at station G2, whereas 157 and 168 species were observed respectively at stations G4 and G6. For Haut Sassandra, stations G3 and G7 respectively presents 208 and 211 species. During this study, 103 species constant were listed against 66 species additional and 170 species accidental. In the floristic list, 73 species are common to all sampling stations. Sorensen index showed a similarity between the sectors and sampling stations. Trophic index based on Phytoplankton composition indicated that lake is from mesotrophy to eutrophy state.

Key words: Phytoplankton, lake, mesotrophy, eutrophy; Ivory Coast.