Effects of deposited marine plastic debris type and deposition period on changes in macroinvertebrate communities

Marine plastic debris (MPD) deposited on the seafloor contributes to the degradation of benthic habitats and impairment of macroinvertebrate ecosystem functions. However, few studies have examined these impacts in detail. We investigated the effects of MPD type (gunny sacks, polyethylene terephthalate bottles, fishing traps, and tires) and deposition period (assessed monthly) on macroinvertebrate habitat and community structure via seven field surveys conducted at Hyeonpo Port, Ulleungdo Island, Korea from 2024 to 2025, with samples collected using a can corer. A total of 102 species (2.3 m²) were identified, with polychaetes (10,559.8 individuals/m²), followed by mollusks (733.5 individuals/m²), and arthropods (194.6 individuals/m²). Species number, density, biomass, and diversity varied according to both MPD type and deposition period. After 7 months of exposure, all MPD types were associated with significant differences in macroinvertebrate community structure compared to the control sites, and the degree of impact on benthic assemblages increased with the exposure period. Among the environmental variables influencing benthic community structure, total organic carbon increased with longer MPD exposure, while mean grain size tended to become coarser. These results imply that long-term MPD exposure can alter macroinvertebrate community composition and potentially promote the formation of novel benthic ecosystems over time. Moreover, the type and physical characteristics of the MPD play crucial roles in determining disturbance intensity and recovery rates in benthic habitats.