The Influence of Microplastic Color and Odor on Feeding Preference in Daphnia magna

The presence of small pieces of plastic, termed Microplastics (MP), in the environment is an area of growing ecological concern, especially for the health of aquatic organisms that ingest them. Little is known about which MP characteristics may influence their likelihood of ingestion by small aquatic organisms, and in turn, their bioaccumulation in animals at higher trophic levels. We used a small freshwater invertebrate, Daphnia magna, that is near the base of the food chain in many aquatic ecosystems, to determine if the color or odor of MPs influenced feeding preference in this species. We hypothesized that D. magna would have a preference for MPs that resemble the color and odor of their algal food source. We conducted experiments exposing D. magna to mixtures of various colors of MP fibers, or mixtures of pristine and biofouled MP fibers. The number of ingested fibers in the intestine of each animal was quantified under a fluorescence microscope to determine if D. magna exhibited a preference for MP based on color or odor. Our results suggest that D. magna do not exhibit a preference for MPs based on color alone. However, in the presence of odorants (biofouled MPs) a significant preference for black MP over green MP is revealed suggesting that olfactory cues play a role in feeding preference and behavior. Our results offer insight into the relationship between MP color and odor characteristics and feeding preference in D. magna.