Microplastics impact simple aquatic food web dynamics through reduced zooplankton feeding and potentially releasing algae from consumer control

Concentrations of microplastics in aquatic environments continue to rise due to industrial production and pollution. While there are various concerns regarding potential deleterious effects of microplastics on ecosystems, several knowledge gaps remain, including the potential for microplastics to directly and indirectly affect biotic interactions and food web dynamics. We explored the effects of environmentally relevant microplastic concentrations on two co-exposed species of herbaceous freshwater crustaceous zooplankton, filter feeding Daphnia dentifera and selective phytoplankton grazers Arctodiaptomus dorsalis. Study organisms were exposed to different concentrations of microplastics (plastic polyethylene microspheres; low = 2.38 × 10 mg/L, medium = 0.023 mg/L, high = 162 mg/L), phytoplankton prey, and predator cues, simulating a simple freshwater food web. Microplastic uptake was greater by D. dentifera, but both species were characterized by decreased algal consumption in the highest microplastic concentration treatment. Importantly, aqueous chlorophyll-a concentrations at the conclusion of the experiment were greater for the high microplastic treatment than all controls and other microplastic treatments. Finally, a predator effect was only apparent for D. dentifera, with greater microplastic uptake in the presence of a predator. We conclude that microplastics may adversely impact the ability of zooplankton to feed on algae and potentially release algae from consumptive control by herbivorous zooplankton. SYNOPSIS: This research aimed to better understand the broader food web effects of environmentally relevant microplastic concentrations on aquatic communities.