Influence of Environmental Factors on the Dynamics and Toxicology of Microcystis and Anabaena in Eutrophic Ponds

Blooms of Microcystis are common in fish ponds in Bangladesh which vary distinctly with season to season. A study on the seasonal changes of Microcystis and Anabaena was carried out over a period of 12 months from March 2021 to February 2022 in two rural fish ponds to see the effect of environmental factors on the seasonal dynamics of these two species. Cyanobacterial community comprised of seven genera and 15 species of which Microcystis was found to be the most dominant genus. Overabundance of Microcyctis may suppress the growth of Anabaena and other microalgal species. In both ponds, Microcyctis was found to be the dominant during the summer and the spring, whereas Anabaena was only characterized in summer. Moderately higher temperature, nitrate–nitrogen, and phosphate–phosphorus enrichment increased the biomass of both Microcystis and Anabaena. Microcystin was found in all the seasons with the highest quantity in summer in the cyanobacteria samples collected from both of the ponds. The highest concentrations of MCs were 22 and 65 μg/L of the sampled water during the peak bloom period of blue-green algae in pond 1 and pond 2, respectively. The high concentration of microcystin in water seems to be a pernicious warning for aquatic organisms as well as human health. Further studies in detail on the relationship between microcystin and cyanobacterial growth under different environmental factors seem to be necessary.