Cross-ecosystem assessment of macroplastic pollution in mangrove, coral reef, seagrass, and beach habitats of tropical small islands.

Marine plastic pollution poses an increasing threat to tropical coastal ecosystems; however, comparative understanding of macroplastic accumulation across interconnected habitats remains limited, particularly in small-island environments. This study assessed macroplastic density and composition across mangroves, coral reefs, seagrass meadows, and beaches on three tropical small islands (Panjang, Semujur, and Ketawai) in western Bangka, Indonesia. Field surveys were conducted in May 2025 using ecosystem-specific transect methods, and macroplastic debris was quantified in terms of abundance, weight, volume, and composition. Macroplastic accumulation exhibited clear habitat-dependent patterns. Across the three islands, beaches consistently recorded the highest debris densities (0.193 ± 0.0083-0.680 ± 0.0310 items/m2), whereas coral reefs exhibited the lowest densities (0.003 ± 0.0005-0.009 ± 0.0011 items/m2). Seagrass meadows showed generally low to moderate accumulation (0.002 ± 0.0003-0.082 ± 0.0102 items/m2), while mangroves exhibited intermediate densities (0.067 ± 0.0027 items/m2). Habitat-level differences were statistically significant (Kruskal-Wallis: χ2 = 78.9, p < 0.001), whereas total debris density did not differ significantly among islands. Food- and beverage-related plastics dominated beach and seagrass habitats, whereas coral reefs consisted exclusively of fishing-related debris. Hierarchical clustering and NMDS ordination (stress = 0.1084) consistently revealed stronger compositional structuring by habitat than by island. PERMANOVA further indicated that habitat accounted for a greater proportion of compositional variation than island identity (R2 = 0.465, p = 0.104). These findings demonstrate that macroplastic accumulation across tropical small islands is primarily structured by habitat characteristics and local retention processes, highlighting the need for habitat-specific mitigation measures and integrated coastal management.