Seasonal and spatial occurrence of plankton and environmental variables in Ogun coastal water on the Bight of Benin

Abstract

The influence of environmental variables on the seasonal and spatial distribution of plankton was studied for 24 months between February 2015 and January 2017 in the marine coastal water of Ogun State, Nigeria. The coastline was stratified into three sampling stations, and surface water samples were collected monthly per station for physico-chemical and plankton analyses. Mean values of physico-chemical parameters were: temperature (28.60±0.27°C), salinity (29.25±0.45‰), pH (7.38±0.07), electrical conductivity (42.13±0.33μS/l), total dissolved solids (29.59±0.30mg/l), dissolved oxygen (6.48±0.07mg/l), phosphate (1.36×10^-2±0.39mg/l) and nitrate (2.25×10^-2±0.65mg/l). The dominant phytoplankton and zooplankton groups were Diatomaceae (42.06%) and Calanoids (25.42%), respectively. Spatial diversity analysis of plankton in the study area showed that the highest (19, 35) species richness and abundance (5703, 12,452) for phytoplankton and zooplankton, respectively occurred in Site 3. Seasonal species richness of phytoplankton and zooplankton was higher in the wet (27, 40) than the dry (23, 38) season. Canonical correspondence analysis explained 77.8% of the influence of environmental variables on plankton distribution. Water temperature, dissolved oxygen, salinity, phosphate, pH, TDS and nitrate were the most marked factors that affected the distribution and abundance of plankton.