Abstract

This paper reported a two season study of diversity, spatial distribution, species composition of phytoplankton and physico-chemical characteristics of the Eastern Obolo River Estuary between June and November 2015 and December and May, 2016. Water conductivity (≥675) showed direct relationship with phytoplankton abundance, turbidity showed strong correlation with species density as well. Species were more evenly distributed across 3 stations at dry season and poorly distributed across 3 stations at wet season. Shannon-wiener index (H)  showed differences within the stations and seasons. Simpson’s diversity index (D) recorded the lowest in station 2 for both seasons. A wide range of phytoplankton species distributed in 5109 individual species, 85 taxa, 16 orders, 8 classes and in 5 divisions during wet season while in dry season 6906 individual species, 84 taxa, 18 orders, 6 classes and 4 divisions were found. The abundance of phytoplankton in dry season occurred in the sequence Baccillariophyta (79%) > Cyanophyta (12%) > Chlorophyta (7%) Dinophyta (2%) while in wet season the sequence was thus; Bacillariophyta (60%) > Chlorophyta (22%) > Cyanophyta (15%) > Dinophyta (3%) > Euglenophyta (0%) respectively. Bacillariophyta were the most dominant both in abundance and species composition in both seasons.

Key words: Chlorophyll-a, evenness, diversity, spatial distribution.