The role of seagrass meadows (Posidonia oceanica) as microplastics sink and vector to benthic food webs

Plastic pollution in marine environments is of global concern, yet its distribution within seagrasses remains poorly understood. We explore the efficiency of Posidonia oceanica in trapping microplastics (MPs) across various components (leaves, rhizomes, sediment), examine their potential transfer through the food web and assess their dispersal using advanced modelling techniques. Field surveys confirm that P. oceanica traps MPs across all components, with the often-overlooked rhizomes accumulating over twice as many MPs (0.2 ± 0.41 items/rhizome) as leaves (0.08 ± 0.28 items/leaf). MP abundance is lower in vegetated sediments than in the adjacent unvegetated seabed (15 ± 1.9 vs. 49 items kg−1 dry weight, respectively). While individual meadow's substrates exhibit low MP levels, the overall concentration increases substantially when accounting for its multi-dimensional structure. Species-specific traits, such as leaf height, and local hydrodynamic processes are likely influencing MPs spatiotemporal distribution. The elevated risk of MPs ingestion by seagrass-associated grazers cannot be confirmed, but further investigation is necessary. This study highlights the effectiveness of a holistic approach in assessing MP pollution within seagrass ecosystems, emphasizing its importance as the way forward. [Display omitted] •Posidonia oceanica acts as a multi-dimensional structure in trapping microplastics.•First known observation of microplastics on seagrass rhizomes.•Higher microplastic loading in bare sediments compared to vegetated sediments.•Local hydrodynamic conditions influence spatiotemporal surface microplastic levels.•Most common polymers identified were PVC (18 %), PI (15 %), DAP, PE and PP (12 % each).