Microplastics Residence Time in Marine Copepods: An Experimental Study

Microplastics are ubiquitous in aquatic environments, and in most marine environments, copepods are the main metazoans. The ingestion of microplastics by zooplankton is linked to various stresses, including oxidative stress, reduced reproductive capacities, and even mortality in nauplii. Microplastics are also reported to serve as vectors for hydrophobic contaminants. Our experimental results highlight that the retention and contact time of microplastics in copepods is quite short. The experimental results show that Parvocalanus crassirostis and Acartia pacifica defecated 75–84% and 61–71% of ingested microplastics within 60 min of ingestion. The observation raises several questions on the hypothesis of microplastic toxicity and ecological stresses: would a 180-minute contact time result in acute toxicity reported by various workers? An interesting observation was that these two copepod species did not consume microplastics larger than 50 µm in size. Considering this fact, inventories of smaller microplastics might be more important for assessing the ecological effects of MP ingestion among primary consumers in the marine food chain. Another important aspect that this study highlights is the likely change in faecal pellet sinking velocities due to the incorporation of MPs, and faecal pellets are probably efficient vectors for MP transport in the aquatic environment.