Environmental variables, algal pigments and phytoplankton in the Atlantic Ocean off the coast of Badagry, Lagos

Abstract

The phytoplankton diversity, environmental variables and algal pigments of the Atlantic Ocean off the coast of Badagry, Lagos were investigated for twelve months between May 2015 and April 2016. The water chemistry characteristics reflected sea water conditions. At the two stations, the range of values recorded for some physico-chemical variables were rainfall (4.1 - 449.3mm), air temperature (23 - 30°C), water temperature (25-31°C), salinity (26.6 - 31.81‰), pH (7.9 - 8.12) and total dissolved solids (26980.1–32900.1mg/L), The phytoplankton diversity consisted of 44 species belonging to three main algal groups namely: 30 species of diatoms (Bacillariophyta) making up 80.49%, five species of blue-green algae (Cyanophyta) making up 13.57% and nine species of dinoflagellate (Dinophyta) accounting for the remaining 5.94%.. Notable species were Coscinodiscus centralis, Coscinodiscus radiatus, Thalassionema nitzschioides and Thalassionema longissima (Diatoms) and a blue-green algae Trichodesmium thiebautii. Nitrate was the key limiting nutrient with regards to algal pigment concentration. The values for the correlation of chlorophyll a (r=0.590, p <0.05), chlorophyll b (r=0.496, p<0.01) and phaeophytin a (r=0.286) with nitrate were significantly positively correlated. Hence, Nitrate is the trigger nutrient for increased algal pigments concentration in the study area.

Keywords: Sea, Lagoon, neritic, diatoms, physico-chemical, phytochemicals