Arriving in better shape: Benthic Microcystis as inoculum for pelagic growth

Changes of the benthic Microcystis community during the time of reinvasion and its influence on the planktonic inoculum were investigated in a laboratory experiment and in a shallow lake (Quitzdorf Reservoir, Germany). Reinvasion was quantified by the diminution of benthic Microcystis abundance, and moreover, by the increase of Microcystis in the water column. Laboratory investigations revealed that the migration of Microcystis from the sediments was elevated by the increase of water temperature from 9 to 15 °C. The extent of reinvasion was more pronounced in light than in dark treatments. Moreover, the reinvasion was accompanied by losses of Microcystis which disappeared from the sediments. In the laboratory experiment it was demonstrated that Microcystis got lost especially under dark conditions. This was supported by the lower photochemical vitality of dark-exposed Microcystis compared to the light-exposed ones.As a consequence of the recruitment from sediments to the water column the morphospecies composition of the Microcystis community changed. Furthermore, the mcyB genotypes of the Microcystis morphospecies were determined. From this morphotype-genotype relation it can be assumed that the composition of Microcystis genotypes at the onset of pelagic growth results from a selective recruitment of mcy+ genotypes from the sediment to the water column.