Abstract
Factors constraining transmission success in parasitic systems remain poorly understood, especially in marine environments increasingly affected by anthropogenic disturbances. Among these, ocean pollution - an insufficiently recognized and inadequately controlled component of global change - poses emerging threats to biodiversity and ecological interactions. In particular, the impact of nanoplastics (NPs), pervasive and biologically active pollutants, on host-parasite dynamics remains largely unexplored. This experimental study examines the effects of NPs exposure on the trematode Maritrema novaezealandensis, a parasite with a complex life cycle involving the snail Zeacumantus subcarinatus and the amphipod Paracalliope novizealandiae as intermediate hosts. Infected snails were exposed for three months to different concentrations of NPs (0, 5, and 20 mg/L). We quantified cercarial (free-swimming infective stages) emergence from snails, assessed their survival and infectivity to amphipods, and investigated impacts on their morphological traits. A significant reduction in cercarial emergence was detected only after several weeks in the 20 mg/L treatment group, suggesting a delayed but cumulative inhibitory effect of high NP exposure. Cercarial survival was also significantly reduced at 20 mg/L, while no statistically significant differences were observed in morphological features or infectivity to amphipods. However, a trend toward reduced tail length at higher concentrations may reflect subtle functional impairments. While infectivity was maintained under short-term exposure, the reduced lifespan of cercariae may limit transmission opportunities in natural settings. These findings highlight the need to include assessment of parasite transmission in ecotoxicological research, as even minor disruptions can cascade through food webs and affect ecosystem stability.