Ecological Drivers of Phytoplankton Community Structure in Egbe Reservoir, Southwestern Nigeria

Phytoplankton communities serve as vital indicators of aquatic ecosystem health. This study investigates how environmental factors are related to the types of phytoplankton found in three places (Ode, Osse River, Downstream) in Egbe Reservoir, Nigeria, using Canonical Correspondence Analysis (CCA) and diversity indices. CCA revealed two axes explaining 99.99% of the constrained variance, demonstrating robust species-environment associations. Axis 1 (65.54%) correlated positively with phosphate, temperature, pH, total dissolved solids, conductivity, dissolved oxygen, and nitrate, but inversely with chlorophyll-a. Genera like Chlorella and Nannochloris were linked to higher nutrient and temperature conditions (positive Axis 1), contrasting with Cryptomonas and various diatoms favouring lower levels. Leptocylindrus exhibited distinct preferences, characterised by negative axis 1 and positive axis 2. Diversity analysis showed that Ode had the highest species richness (17 taxa and 242,917 individuals). The Osse River exhibited the highest diversity (Shannon = 2.05, Simpson's 1-D = 0.8162) and evenness (0.5976), reflecting a more balanced community structure. Downstream stations displayed a diminished diversity and increased dominance. These findings highlight the profound impact of physicochemical gradients on phytoplankton, which is vital for biomonitoring and management of tropical reservoirs.