The prevalence of microplastics is increasing in marine ecosystems and posing significant threats to marine organisms, especially when ingested. Mnemiopsis leidyi, a species of ctenophore, is an important primary predator within the food web of western Atlantic coastal ecosystems. These macro-invertebrates feed principally on zooplankton and are consumed by a variety of fish, birds, and sea turtles. The purpose of this study was to see if, and subsequently how, ctenophores interacted with microplastic beads (250-300 μm). Specifically, we were interested in (1) whether or not ctenophores would ingest microplastic beads, (2) whether or not the microplastic beads would adhere to the external surface of ctenophores, and/or (3) whether or not microplastic beads would become caught within the lobes of ctenophores. Ctenophores were individually housed in aquaria with an ecologically relevant concentration of 50 microplastic beads: 500 prey items per liter of seawater (experimental N=6) or only prey items (control N=6). Ctenophores were observed at ten minute intervals for two hours. At each interval, the number of microplastic beads present in the stomodeum, attached externally, and within the lobes was counted.
Results/Conclusions
All ctenophores in the experimental groups had at least one form of interaction with microplastic beads and interacted with microplastic beads for a total of 72% of the experiment’s duration. Ctenophores that were exposed to microplastics and ingested them (n=5; 83%) had microplastic beads present in their stomodeum for an average of 43% of the experiment’s duration. It took ctenophores approximately 36 minutes on average to egest microplastic beads once they were present in the stomodeum. Ctenophores that had microplastic beads adhere to their external surfaces (83%) spent a total of 31% of the experiment’s duration with microplastics attached to them. On average, it took ctenophores 14 minutes to rid themselves of microplastics attached externally. Finally, all ctenophores in the experimental groups had microplastics caught within their lobes for an average of 35% of the experiment’s duration. It took ctenophores an average of 12 minutes to remove microplastics from within their lobes. The results of this study demonstrate the potential for microplastics to bio-accumulate within the food web, given that all ctenophores interacted with microplastics for a majority of the time in which they were exposed.