Sequence of Microcystis colony formation during recruitment under natural conditions

Colony formation by Microcystis is considered to play an important role in bloom development. Population dynamics of benthic and pelagic Microcystis colonies and single cells were investigated in Lake Taihu during recruitment from the sediment. Our results showed that the number of Microcystis single cells in both the water column and sediment was much higher than that of colonies during winter and early spring. In late May, cell density of single cells in the water column was greater than 1 x 10(5) cells ml(-1). This result also suggested that only a portion of the Microcystis single cells formed colonies during recruitment. Microcystis single cells formed colonies on the surface of the sediment where the temperature and light intensity were lower than in the water column. The temporal variation in morphology and colony size of Microcystis in both the water column and sediment demonstrated that a possible sequence of Microcystis colony formation is that colony-forming process begins with loose amorphous colonies formed from single cells in the sediment, then changing to firm amorphous colonies. Afterwards, firm amorphous colonies rise into the water column and some form typical M. ichthyoblabe colony morphology.