Radular morphology, elemental composition, and mechanical properties determine the plastic-eroding ability of molluscan grazers

Microplastics (MPs) have recently attracted considerable attention as a major marine pollutant capable of infiltrating the digestive tracts, tissues, and even cells of marine organisms, potentially causing severe biological impacts. To date, the primary drivers of MP generation in marine environments have been regarded as abiotic factors such as wind, waves, and ultraviolet radiation, with coastal and surface waters recognized as the main source areas. In benthic environments, however, the activities of bioeroding organisms, particularly benthic animals, may also contribute to MP production. Molluscan grazers inhabiting rocky substrates use the radula to scrape algae and sediments from surfaces. Thus, when plastic debris accumulates on the seafloor, molluscan grazing activity may erode plastic surfaces and generate MPs. In this study, we examined four molluscan grazers-two chitons, one limpet, and one topshell-to evaluate whether their feeding activities could erode five types of plastics. We also investigated the relationship between the erosion capacity and the morphology, elemental composition, and mechanical properties of the radular teeth using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and nanoindentation analyses. The results showed that all tested plastics were eroded by grazing activity. Species with radular teeth enriched with hard materials such as iron and silica were capable of eroding even hard plastics, whereas those with sharp-tipped teeth caused more pronounced surface damage. Most MPs produced by these grazers were smaller than several tens of micrometers, indicating that such fine particles could pose ecological risks to a wide range of marine organisms.