Temperature-dependent akinete formation strategies of the harmful cyanobacterium Dolichospermum circinale

•The harmful cyanobacteria Dolichospurmum circinale was found to form akinetes over a wide temperature range.•The rate of akinete formation was high at low temperatures and decreased with increasing temperature. By contrast, the total akinete concentration formed and its ratio to the total number of cells were higher at higher temperatures than they were at lower temperatures.•With increasing temperature, vegetative cell growth rate and empty akinete formation rate increased together. Empty akinetes accounted for the majority of the total akinete concentration and proportion at higher temperatures.•The change in vegetative cell size was proportional to the increase in growth rate with increasing temperature, while the akinete size was larger at lower temperatures than it was at higher temperatures.•Akinete formation and germination may be closely linked during summer cyanobacteria blooms. Cyanobacteria from the orders Nostocales and certain Stigonematales form akinetes, spore-like dormant cells that allow them to survive adverse environmental conditions. Temperature is known to be one of the key factors affecting akinete formation, but there is currently little known about akinete formation during cell growth over a wide range of temperature conditions and its relation to the overall survival strategy of cyanobacteria. Therefore, in the current study, we conducted a temperature-controlled experiment to analyze the akinete formation of a harmful cyanobacterium Dolichospurmum circinale using a growth chamber. We measured the concentration and size of both vegetative cells and different types of akinetes (free, attached, and empty type) under varying temperatures (5–25 °C). We also analyzed the buoyant ability and vertical migration velocity of trichomes along with changes in the volume of vegetative cells and akinetes. The total akinete concentration and ratio (number of akinetes to total number of cells) were both found to be higher at high temperatures (20–25°C) than they were at low temperatures (5–10°C) (p