Seasonal Shifts in the Morphological Traits of Bloom-Forming Cyanobacteria in Lake Chaohu, China

Harmful cyanobacterial blooms in eutrophic water bodies pose a major threat to the environment and to human health. The morphological functional traits of cyanobacteria play important roles in maintaining their competitive advantages. To explore the regulatory mechanisms of the morphological functional traits of different bloom-forming cyanobacteria, we performed a one-year-long phytoplankton survey from November 2016 to October 2017 in Lake Chaohu, China. The colony size and cell diameter of the dominant cyanobacteria were measured, and their relationships were analyzed. The results showed that Dolichospermum flos-aquae and Microcystis aeruginosa were the dominant cyanobacteria in the lake. Microcystis was the dominant species during the summer; the growth of Dolichospermum growth surpassed that of Microcystis, and Dolichospermum became the dominant species in the late autumn, winter and spring. From winter to spring, the colony size of Dolichospermum decreased from 222.25 mu m to 10.51 mu m, and the individual cell diameter increased from 6.5 mu m to 7.4 mu m. From summer to autumn, Dolichospermum showed enlarged colony sizes and reduced cell diameters. The Microcystis colony size increased from 83.71 mu m in the spring to 196.71 mu m in the summer and autumn, while cells diameter remained essentially at 3-4 mu m from March to October in Lake Chaohu. The relationship between colony size and cell diameter in Dolichospermum was significantly positive, while that of Microcystis was not significant. These results suggest that Dolichospermum may maintain biomass through a trade-off between cell diameter and colony size, and that a flexible morphological regulatory mechanism exists. This study seeks to improve our understanding of how bloom-forming cyanobacteria maintain their dominance by regulating their morphological traits.