The widespread use of plastics has led to ecosystem risks, which serve as ideal substrates for biofouling in aqueous environments, spreading ecological hazards. In this study, we established a simulation system incorporating Mytilus coruscus larvae and buoyant plastic rope fragments, using polyethylene rope fragments as substrates to assess the attachment behavior of the larvae and the duration of their buoyancy, in order to investigate the potential role of buoyant plastic rope fragments in facilitating larval dispersal and evaluate their ecological implications. The results demonstrated that larvae successfully attached to plastic rope fragments, showing a preference for the rougher ends, and extended their pelagic phase by up to 25 days. The average attachment count of larvae on plastic rope fragments coated with mixed microalgal biofilm (50.0 ± 23.6 ind/5 cm) was lower than on rope fragments without biofilm (70.6 ± 19.4 ind/5 cm), but the difference was not statistically significant (p >
0.05). Particle dispersal simulations indicated that the extended pelagic phase significantly increased the northward dispersal range of the larvae. Based on these findings, we suggest that the increased dispersal range may influence the genetic differentiation of M. coruscus populations. These findings enhance our understanding of the ecological impacts of plastics on M. coruscus and other sessile organisms.