Population dynamics and akinete formation of an invasive and a native cyanobacterium in temperate lakes

Abstract

Most cyanobacteria of the order Nostocales in the temperate zone survive winters in the sediment as akinetes. The present study compared seasonal population dynamics and the formation of akinetes of the invasive cyanobacterium Cylindrospermopsis raciborskii with the native species Aphanizomenon gracile in three German lakes. The effect of light, temperature and growth rate on akinete formation was investigated in the field over a 3-year period and additionally in a culture study with nine different C. raciborskii and A. gracile strains. The results of the field study showed, for both species, a strong negative correlation between akinete formation and light and temperature, and a weaker negative correlation between akinete formation and the net growth rate of the populations. Akinete formation of the isolates was mainly affected by temperature and not by light intensity. The investigation of the seasonal population dynamics showed that the growth period of C. raciborskii in the pelagic zone was on average 64 days shorter compared with A. gracile. However, the amount of akinetes produced by C. raciborskii during 1 year was, in more than half of the cases, similar or higher than that produced by native A. gracile. The ratio of akinetes to total cell number was significantly higher for C. raciborskii compared with A. gracile, 9 and 2%, respectively. Therefore, we conclude that C. raciborskii populations in temperate lakes have a similar potential for an akinete-based life cycle performance as do the native A. gracile populations.