Abstract

The effect of hydroclimatic conditions on phytoplankton was investigated in Ejirin, part of Epe lagoon, south-western Nigeria from December, 2012 to May, 2013. The data obtained for hydroclimatic features responded to rainfall pattern during the study period. The water remained acidic throughout the sampling period as pH value was ≤ 6.6 and salinity value ≤ 0.01%. The micronutrients varied throughout the sampling period and showed a correlation with rainfall. Chlorophyll a (Chl. a) concentration showed a correlation with conductivity, rainfall and surface water temperature, with a mean value of 0.021 mg L-1. Transparency, salinity, silicate and reactive phosphate showed a dominant effect on the phytoplankton community. The total number of phytoplankton species recorded during dry months differed significantly with that of the wet months (t* = 2.723, P > 0.05). A total of 105 species belonging to 5 divisions were recorded throughout the study period: Bacillariophyta (81.3%); Cyanobacteria (10.71%); Chlorophyta (6.5%), Eugleanophyta (1.35%) and Chrysophyta (0.13%). Diatoms were the dominant species in both the dry and wet months with 12 centric and 35 pennate forms. Phytoplankton density correlated significantly with silicate and TDS, indicating the possible effect of silicate on the diatoms and TDS on the whole community.

Key words: Cyanobacteria, phosphate, salinity, transparency.