The composition and diversity of planktonic algae in a sluggish tidal freshwater/brackish mangrove dominated creek (Ipa Itako) part of the Lagos lagoon was investigated for twelve months (February 2010 - January 2011). The surface water pH varied between 6.5 (December 2010) and 8.6 (August 2010) indicating a slightly acidic to alkaline nature of the creek. The salinity was higher during the dry months (November- April) and phosphate - phosphorus and nitrate-nitrogen recorded highest values (3.50 and 16.70 mg/L) respectively in June, 2010. Ninety three species belonging to forty nine genera from five classes (Bacillariophyceae, Chlorophyceae, Euglenophyceae, Cyanophyceae and Xanthophyceae) were recorded. Bacillariophyceae constituted the most abundant group making up 72.85% of cells/ml followed by the Chlorophytes (18.02%) then the blue green (7.65%), euglenoids (1.40%) and xanthophytes (0.07%) with only Vaucheria sp. recorded as a representative of the group. Higher phytoplankton diversity and cell counts were recorded in the dry months than in the wet months. Navicula, Pinnularia, Cymbella (Diatoms) and Closterium (Chlorophyceae) were more frequently occurring species. Community structure analysis indices used indicated a diverse but stressed environment.
Key words: Diversity, phytoplankton, creek, eutrophication.
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