Microplastics (MPs) enter aquatic food chains via ingestion by primary consumers and biomagnify through higher trophic levels. This study elucidated the impacts of this by assessing the effect of MPs on Daphnia magna’s growth and reproduction with exposure to Chlorella algae as an additional food source. Daphnia were placed into four groups: Control, added MPs (2.22 mg/mL), added Chlorella, and both treatments. The Control and Chlorella-only groups maintained healthy heart rates at averages of 200±4 and 201±3 bpm, respectively; however, the MP-only group saw a significant decrease to an average of 181±2 bpm (p<0.001). Chlorella promoted MP ingestion, amplifying its negative impacts: the heart rate of this group was only 168±2 bpm (p<0.05). This same trend was observed for the body dimensions of the Daphnia, as groups solely exposed to MPs experienced significant decreases (p<0.001). Daphnia exposed to MPs developed ephippia, indicating a switch from sexual to asexual reproduction. This resulted in a significant reduction in reproduction, decreasing population sizes (p<0.001). Each negative trend was magnified by the presence of Chlorella (p<0.05). Thus, this study’s findings indicate that the accumulation of MPs can decrease genetic diversity and population sizes among Daphnia due to increased asexual reproduction, leading to adverse effects on aquatic ecosystems. Future work should utilize oxidative stress assays to confirm that MPs caused the reproductive change.

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