Involvement of microcystins, colony size and photosynthetic activity in the benthic recruitment of Microcystis

Abstract

Cyanobacterial blooms in aquatic environments are a worldwide problem that greatly depend on the recruitment of benthic Microcystis species. In addition to environmental factors, physiological characteristics are also crucial for benthic recruitment of Microcystis, although the exact details remain poorly understood. In the present study, we studied the involvement of physiological characteristics in benthic recruitment from three aspects: photosynthetic activity, colony size and intracellular microcystin (MC) content. After UV irradiation the Microcystis cells were damaged and in poor physiological state. Normal benthic Microcystis (NBM) exhibited higher recruitment than damaged benthic Microcystis (DBM). This might be explained by the difference in photosynthetic activity. Small benthic colonies (20–60 μm) could reinvade the water column from sediments more easily than large colonies. Furthermore, poor physiological state was correlated with lower survival of large colonies (140–220 μm) which might decompose into smaller colonies (40–80 μm). Toxic Microcystis not only survived more easily than non-toxic ones in sediments but also recruited more readily into the water column from sediments. This might be due to the presence of intracellular MCs. During the benthic phase, toxic Microcystis might consume or release intracellular MCs to acclimate to benthic environment. We also found that sediment mixing in the form of passive suspension facilitated recruitment, but physiological characteristics, an active process, played a more decisive role. This knowledge on the physiological characteristics of Microcystis expands our understanding of benthic recruitment.