Composition, Distribution and Spatio-Temporal Dynamics of Phytoplankton Community of the Tropical Freshwater Stream, Ikoro Stream, Edo State, Nigeria

The objective of this paper is to investigate the Composition, Distribution and Spatio Temporal Dynamics community of the tropical freshwater stream, Ikoro Stream, Edo State, Nigeria using appropriate standard methods. A total of 83 phytoplankton taxa comprising five taxonomic divisions, namely Chlorophyta (55%), Bacillariophyta (32%), Cyanophyta (7%), Euglenophyta (5%) and Rhodophyta (1%) were identified. The Chlorophyta were mainly Desmidiaceae; Bacillariophyta were mainly Diatomaceae and Naviculaceae; Cyanophyta represented by Chroococcaceae, Nostocaceae, and Oscillatoriaceae; Euglenophyta represented by Euglenophyceae and Rhodophyta by the single species Batrachospermum vagum. Fragillaria sp. was identified as the most ubiquitous taxon, with an overwhelming 96% occurrence across almost all sampling months and stations. Other highly frequent taxa included Surirella elegans (67%), Pinnularia cardinaliculus (63%), and Cladophora oligoclona (54%). Conversely, Chlorophyta richness was heavily driven by true desmids (e.g., Closterium, Cosmarium, and Micrasterias), alongside filamentous forms such as Spirogyra and Oedogonium. Spatio-temporal dynamics were influenced by seasonal climate shifts. Spatial variations were minor, though Station 3 displayed a slightly more robust distribution of desmids and euglenoids later in the sampling season. From a bio-indicator perspective, the minimal presence of organic pollution markers - specifically Cyanophyta (Anabaena, Oscillatoria) and Euglenophyta (Euglena, Phacus) indicates that Ikoro Stream is relatively pristine and free from heavy agricultural or anthropogenic eutrophication. This ecological integrity is further corroborated by the presence of the red alga Batrachospermum vagum (21% occurrence), a sensitive indicator of clean, well-oxygenated, flowing lotic systems. On the whole, the study demonstrates that Ikoro Stream maintains a stable ecological balance, providing crucial baseline data for local watershed conservation and management.