Physiological variations of bloom-forming Microcystis (Cyanophyceae) related to colony size changes during blooms

Abstract

Li Y. and Li D. 2012. Physiological variations of bloom-forming Microcystis (Cyanophyceae) related to colony size changes during blooms. Phycologia 51: 599–603. DOI: 10.2216/11-126.1Microcystis has been intensively studied, but previous studies using laboratory cultures did not explain why colony size differed widely and frequently during natural blooms. This study was designed to unravel the mechanism for changes in biomass that accompany different sized colonies and to establish the basis for physiological variation. Monitoring colonies during blooms indicated that biomass variations for different sized colonies were associated with the frequent alteration of environment factors. Large-sized colonies had a higher carotenoid content (F = 10.74, P = 0.029) and phycocyanin content (F = 8.28, P = 0.041) during July and August; small-sized colonies had a higher total carbohydrate content (F = 9.43, P = 0.033) and higher nitrate reductase activities (P < 0.01, ANOVA). No significant difference was observed for alkaline phosphatase activities among different sized colonies (P < 0.05, ANOVA). We proposed that some key environmental factors combined with physiological variations in different sized colonies resulted in colony size succession. The selection of colony size may be an adaptive mechanism that promotes the formation, dominance and persistence of cyanobacterial blooms in eutrophic water bodies.