Marine Plastic Debris Entrapped in Tube Decorations of Plumed Worm: Evidence of a Novel Biological Sink in Intertidal Mudflats

Marine plastic pollution research has focused primarily on debris in water columns and sediments, as well as plastics ingested by marine organisms, while the incorporation of plastics into biogenic structures by habitat-engineering organisms remains underexplored. Here, we investigated the tube-decorating polychaete Diopatra sp. on intertidal mudflats of Hanagae Beach, South Korea, to assess whether plastic debris is utilized as tube-building material. While no plastic particles (> 2 mm) were detected in surface sediments, all examined Diopatra tubes ( n = 48) contained plastics, averaging 4.73 plastic particles per tube. Both Diopatra abundance and tube-entrapped plastics increased with distance from the shoreline, suggesting hydrodynamic mediation of habitat suitability and plastic retention. FTIR spectroscopy revealed that fibers dominated the incorporated plastics, primarily derived from Abandoned, Lost, or otherwise Discarded Fishing Gear (ALDFG). Notably, per-tube plastic loads substantially exceeded ingestion-based accumulation levels reported for other benthic invertebrates, underscoring bioconstruction as a distinct and more efficient retention mechanism. We propose that, at least within intertidal systems, tube-decorating polychaetes may act as a biological reservoir for plastic debris through tube construction, whereby their biogenic structures can reflect pollution levels that may be overlooked by conventional sampling approaches.