Entanglement of Daphnia magna by Fibrous Microplastics through “Hook and Loop” Action

Entanglement, often associated with the interaction of large marine plastics and larger animals, has not yet been reported in the context of microplastics (MPs) and small organisms. In this study, Daphnia magna was exposed to fibrous and fragmentary MPs at concentrations ranging from 1 to 1000 items/mL for 7 days. The results revealed that fibrous MPs tended to entangle with the second antennae and tail claws of D. magna, whereas fragmentary MPs merely adhered to the surface of the daphnids but do not exhibit entanglement. Additionally, the swimming speed and projected area of swimming trajectories of daphnids significantly decreased in the 100 items/mL group compared with the control. However, the occurrence of entanglement and slow swimming was less pronounced in the 1000 items/mL group due to the aggregation of fibrous MPs. Scanning electron microscopy revealed that D. magna possessed a rich spine structure on the surface of their bodies, particularly on their antennae and tails. The entanglement of D. magna by fibrous MPs resembled the action of manufactured "hook and loop". Overall, the results of this research revealed that entanglement is observed in small animals exposed to fibrous MPs, highlighting the direct biological effects of MPs beyond ingestion.