Diversity of harmful diatom species in the upper reaches of Bonny Estuary, Niger Delta, Nigeria

Abstract

This research was carried out to assess the abundance and distribution of harmful diatoms in the upper reaches of the Bonny Estuary between December 2021 and November 2022. Three sampling stations were established using the ArcGIS tool.Microalgae species were sampled with 20μm mesh plankton net. Some physicochemical parameters were determined in situ, while nutrients were analyzed in the laboratory using the APHA 4500 Method. A total of 8 genera and 18 species, with four genera of centric diatoms (8 species) and four genera of pennate diatoms (10 species) were recorded. The least mean density value (318.33 CellsL -1 ), was recorded for Thalassiosira eccentrica species, while Cyclotella meneghiniana recorded the highest density value (1146.67 CellsL -1 ), for centric harmful diatoms. Nitzchia vermicularis recorded the least density value (602.34 CellsL -1 ) and Navicula amphibola recorded the highest density value (2022.34 CellsL -1 ) for pennate harmful diatoms across the sampled stations. The percentage composition recorded 64% for pennate diatoms and 36% for centric diatoms.Salinity and temperature showed a strong positive correlation with pennate diatoms and pH, nitrate and phosphate also showed a strong positive correlation, with harmful centric diatoms. Diversity indices revealed Shannon's index ranged between 2.77-2.86 and species evenness ranged between 0.89-0.91, while Margalef range value 2.59-2.60 were considered moderately stable. All species were evenly spread across all stations. Further research is necessary to develop effective management strategies that can mitigate the possible formation of blooms and their harmful effects in the upper reaches of the Bonny Estuary.