Chlorophytes prolong mixotrophic Ochromonas eliminating Microcystis: Temperature-dependent effect.

Cyanobacterial blooms, caused by eutrophication and climate warming, exert severely negative effects on aquatic ecosystem. Some species of protozoans can graze on toxic cyanobacteria and degrade microcystins highly efficiently, which shows a promising way to control the harmful algae. However, in the field, many different species of algae coexist with Microcystis and may affect protozoans eliminating Microcystis. Therefore, in this study, we assessed the impacts of chlorophytes, a type of beneficial algae for zooplankton and common competitors of cyanobacteria, on flagellate Ochromonas eliminating toxin-producing Microcystis at different temperatures. Our results showed that Ochromonas still eliminated Microcystis population and degraded the total microcystins with the addition of chlorophytes, although the time of eliminating Microcystis was prolonged and temperature-dependent. Additionally, in the grazing treatments, chlorophytes populations gradually increased with the depletion of Microcystis, whereas Microcystis dominated in the mixed algal cultures without Ochromonas. The findings indicated that although chlorophytes prolong mixotrophic Ochromonas eliminating Microcystis, the flagellate grazing Microcystis helps chlorophytes dominating in the primary producers, which is significant in improving water quality and reducing aquatic ecosystem risks.
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