Microplastic Contamination across Interconnected Seagrass Meadows and Coral Reefs: Divergent Patterns and Limited Convergence

To address knowledge gaps in microplastic (MP) fates within connected ecosystems, this study analyzes divergence and convergence across interconnected seagrass and coral habitats. Convergence was limited: Only 16% of MP categories were shared (notably black fibrous PET), and high-density MPs consistently accumulated in sediments in both ecosystems. However, divergence was pronounced. Seagrass meadows acted as selective filters that facilitated sedimentation of larger MPs, leaving smaller fractions to dominate transport to reefs, where they accumulated on coral surfaces and tissues. Notably, biological selectivity altered this pattern internally: while small MPs were prevalent, coral tissues disproportionately accumulated large (1–2 mm), high-density transparent fibers, likely triggered by physical entanglement and prey-mimicking optical cues. Seagrass leaves intercepted high-density MPs on surfaces, whereas corals were highly susceptible to internal accumulation within tissues and skeletons. Furthermore, coral skeletons served as long-term archives sequestering diverse, predominantly high-density MPs, while seagrass leaves acted as short-term dynamic traps with significantly higher surface abundance. Specifically, surface accumulation was morphologically driven, whereas internal incorporation in corals was biologically regulated and decoupled from surface loads. Mechanistically, these patterns suggest that intrinsic biological modulation is the primary driver of MP heterogeneity between ecosystems. These findings highlight the need for habitat-specific risk assessments.