Influence of light, sediment mixing, temperature and duration of the benthic life phase on the benthic recruitment of Microcystis
Résumé
The benthic recruitment of Microcystis was assessed in vitro in order (i) to compare the relative influence of the main abiotic factors, and (ii) to investigate the impact of the duration of the benthic life stage. Different benthic populations sampled in a 45 m deep artificial lake, with benthic life phases ranging from a few weeks to almost 3 years, were used to test the impact of three temperatures (4, 7 and 178C), the absence or presence of light and sediment mixing on Microcystis recruitment. In this study, sediment mixing was the only physical factor found to promote recruitment, indicating that passive resuspension plays a much more important role in the recruitment of Microcystis than light and temperature. Moreover, recruitment occurred from all benthic populations, including one that was nearly 3 years old. No difference in the proportion of recruited cells was observed before and after the usual overwintering period, suggesting that the annual benthic overwintering does not impair the ability of Microcystis to inoculate the water column in the following spring. However, in the oldest population, the proportions of recruited cells were lower under all the experimental conditions tested, indicating a decrease in the ability of older benthic populations of Microcystis to contribute to the recruitment process.