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Microplastics interfere with mixotrophic Ochromonas eliminating toxic Microcystis
Summary
Researchers investigated how microplastics of two sizes (0.07 and 3 µm) affect the ability of the mixotrophic flagellate Ochromonas gloeopara to predate on and eliminate toxic Microcystis aeruginosa blooms. They found that microplastics at all tested concentrations and sizes reduced maximum Microcystis abundance but also harmed Ochromonas, suggesting that microplastic pollution could disrupt the natural biocontrol of harmful algal blooms in freshwater systems.
Microplastics with different sizes exist widely in fresh waters, which may affect the interspecific dynamics between predator and prey. The flagellate Ochromonas gloeopara can efficiently eliminate Microcystis aeruginosa and degrade microcystins, which shows great potential for controlling harmful Microcystis. In order to evaluate the effects of microplastics on O. gloeopara eliminating Microcystis, we designed an experiment of O. gloeopara feeding on Microcystis under different sizes (0.07 and 3 μm) and concentrations (0, 0.4, 0.8, 1.6, and 2.0 mg L) of microplastics. The results showed that maximum abundance of M. aeruginosa decreased significantly with addition of microplastics, regardless of the size and concentration. O. gloeopara can ingest the microplastics and suffer from their adverse effects. The maximum abundance of O. gloeopara decreased with enhancing concentrations of 3 μm microplastics during the process of O. gloeopara eliminating M. aeruginosa, whereas 0.07 μm microplastics did not affect the growth of O. gloeopara obviously. During the period of exposure under microplastics, clearance rate of O. gloeopara on M. aeruginosa decreased with the increasing concentrations of microplastics. Specially, 3 μm microplastics had a stronger reduction on clearance rate of O. gloeopara. The time to M. aeruginosa extinction was prolonged with the increasing concentrations of microplastics in both sizes. Comparatively speaking, 3 μm microplastics had a stronger delayed effect on the removal of Microcystis. These findings suggest that microplastics can interfere with protozoa eliminating toxic Microcystis, which may aggravate their adverse impacts on aquatic ecosystem.