Changes in particle mixing by benthic infauna induced by microplastics: implications for nitrogen cycling in marine sediments

Microplastics modify the relationship between benthic animals and their environment and can alter ecosystem functioning in seafloor habitats. We experimentally investigated shifts in the functional roles of 2 large deposit feeders that influence biogeochemical processes in marine sediments, the tellinid bivalve Macomona liliana and the maldanid worm Macroclymenella stewartensis , as well as a combination of these 2 species. We measured the particle mixing capacity as a proxy for interactions between macrofauna and their environment when exposed to microplastics. Increasing microplastic concentrations (polypropylene, diameter of <500 µm) impaired the deep-burrowing behaviour of M. stewartensis . Particle mixing by M. liliana was not significantly affected by microplastics. Contamination levels of microplastics also modified the relationship between the 2 species. Our study shows that microplastics influence the process of macrofauna transporting particulate resources and regulating nutrient cycling. The degree to which microplastics influence benthic fluxes (oxygen and nitrogen) varies with the functional traits of the macrofaunal species and the concentrations of the microplastics.