Plankton Composition in Relation to Water Quality in the Coastal Waters of Nigeria

Coastal waters of Ondo State, Nigeria have diverse assemblage of fish, yet there is dearth of information on its plankton composition. This study investigates plankton components in relation to physicochemical characteristics of the coastal waters bordering Olotu, Ayetoro and Bijimi in providing baseline information that can be used for planning and implementation of policies for monitoring, impacts assessment and conservation. Surface water samples were collected on monthly basis from March to June 2015 to analyze physicochemical parameters while plankton net of 55μm mesh size was used for collection of plankton using standard methods prescribed by APHA. The light and dark bottle method was used to determine primary productivity. Shannon-wiener, Margalef and Equitability Indices were used for diversity. Values of the physicochemical parameters observed ranged as follows: temperature, 27.47±2.06-29.27±0.31ºC; turbidity, 43.43±0.91-65.33±2.52NTU; pH, 5.54±0.31-6.12±0.30; BOD, 2.20±0.29-5.43±0.54 mg/l; COD, 6.08±2.71-6.66±1.52 mg/l; dissolved oxygen, 6.39±0.39-7.78±0.19 mg/l and salinity, 2.03±0.06-3.77±0.04 mg/l. Fifteen species of phytoplankton and three developmental stages of zooplankton were recorded. Phytoplankton accounted for 83.3% as against 16.7% zooplankton. Diatoms (93.3%) and dinoflagellates (6.7%) represented phytoplankton whereas 66.7% of zooplankton belonged to the phylum Arthropoda. Primary productivity ranged between 132.194±13.48m-3hr-1 and 134.48±15.27m-3hr-1. Some dominant species recorded were Coscinodiscus, Biddulphia, Copepod, Skeletonema and Ditylum. pH and Temperature were major determinant of the composition, diversity and abundance of plankton. The observed plankton group indicates the suitability of the creeks as habitat and breeding ground for diverse aquatic species. The water quality falls within acceptable range hence the environment can be classified as healthy ecosystem.