Abstract
The physico-chemical characteristics, phytoplankton composition and distribution at the East mole area of the Lagos harbour were investigated between January and June, 2012. The physico-chemical conditions varied between high brackish and sea water chemistry. Records were Air (26 - 330C) and Water temperatures (28 - 310C), Salinity (19.40 - 30.720/00), Nutrients (Nitrate ≥ 3.11 mg/L; Phosphate ≥ 0.65 mg/L, Sulphate ≥ 878.6mg/L), alkaline pH (7.75 – 8.48), Transparency (141.2 - 236.5cm), Alkalinity (33 - 85.2mg/L), Conductivity (32700 – 49,600 µS/cm), Dissolved Oxygen (4.8 - 5.4mg/L) and Chlorophyll a concentrations (8.5 - 10.1mg/L). Chlorophyll a concentration was positively correlated with Salinity (r = 0.81), Total Dissolved Solids (r = 0.80), Conductivity (r = 0.81), Rainfall (r = 0.13), Phosphate (r = 0.87), Sulphate (r = 0.65), Silica (r = -0.62), Nitrate (r = 0.10), Dissolved Oxygen (r = -0.38) and Air temperature (r = -0.61). The phytoplankton diversity consisted of three main algal groups namely - Diatoms, Blue-green algae and Dinoflagellates. A total of 32 species belonging to 18 genera were observed. Diatoms formed the more abundant group making up 22 species from 13 genera. The Blue-green algae recorded five species from three genera and Dinoflagellates with five species from two genera. In terms of diversity, the dry season (Jan. – Apr. 2012) recorded a relatively higher phytoplankton diversity (S) and abundance (N) than the wet season. In terms of diversity, the Diatoms, reported 68.75% (Centric - 50% and Pennate diatoms –18.75%), while the Blue-green algae and the Dinoflagellates recorded 15.63% respectively. In terms of phytoplankton abundance, the month of February recorded the highest outcome. The biological indices reflected a similar trend of occurrence as the species composition and distribution. Notable species were Coscinodiscus centralis, Coscinodiscus radiatus, Synedra crystallina, Trichodesmium thiebatii, Ceratium bicephalum and Oscillatoria trichodes.