Phytoplankton Diversity in the Cross River Estuary of Nigeria

Studies on the species composition, relative abundance, spatial distribution and diversity of phytoplankton assemblages in the Cross River Estuary were carried out for twenty-four months, across six (6) sampling stations. A total of 105 species of 57 genera, belonging to 5 families was observed. Bacillariophyceae (Diatom) was the most abundant phytoplankton family, constituting 71.58% of total Algal density, followed by Chlorophyceae (Green algae) with 13.84%, Cyanobacteria (Blue-green algae) with 12.69%, while Euglenophyceae (Green flagellates) and Dinophyceae (Dinoflagellates) recorded 0.88% and 1.01% respectively, of total phytoplankton abundance. Bacillariophyceae showed progressive importance from stations 1 to 6 while chlorophyceae and Euglenophyceae were more abundant in stations 1, 2, and 3. Cyanobacteria however, showed no spatial bias, whereas Dinophyceae were observed only in stations 4, 5 and 6. Bacillarlophyceae was the most dominant family, while chlorophyceae and cyanobacteria were observed to be subdominant groups. Similarity of species occurrence was generally observed in stations 1 and 2, station 3 and 4 and stations 5 and 6. Analysis of variance (ANOVA) showed significant variation (P<0.05) in community structure between stations 1, 5 and 6 whereas stations 1, 2 and 3 showed no significant difference (P>0.05) in composition of phytoplankton assemblages. High abundance of certain cyanobacteria taxa indicated environmental degradation.