Variation in Colony Size of Microcystis aeruginosa in a Eutrophic Lake during Recruitment and Bloom Formation

Variation in colony size of Microcystis aeruginosa was investigated in Lake Taihu during recruitment and bloom formation from March to June. Single cells remained at the same level throughout the study period, making up between 30 and 40% of total units. Small colonies of < 20 cells also constituted a major part of the recruited population, and larger colonies with >20 cells were not observed until mid-April. Much larger colonies composed of >200 cells were only observed occasionally in May but were frequent in June when a surface bloom formed in the lake, suggesting that colonies consisting of hundreds or thousands of cells are necessary to form blooms. Although the number of large colonies was small, the cells of these large colonies accounted for over 90% of the total population. The mean number of cells per colony increased significantly from May and reached over 120 in June. which coincided with bloom formation.