Microplastic Ingestion from Contaminated Prey in the Bearded Fireworm Hermodice carunculata (Pallas, 1766): Evidence for Rapid Excretion and Low Degradation

Microplastics (MPs) are widespread contaminants in seabeds, where they are bioavailable to benthic organisms including polychaetes. Among them, the bearded fireworm represents a potential target for MP, given its opportunistic predatory and scavenging habits, reaching high densities and displaying a wide expansion range in the Mediterranean Sea. In this pilot bench-scale study, we investigated MP ingestion and egestion in this species through a simplified two-level trophic chain, using mussels as prey. Mediterranean mussels were first exposed to fluorescently labelled polystyrene microspheres (micro-PS, nominal size of 10 µm) and offered to fireworms. Within three days, fireworm faecal pellets, intestines, and body fluids were collected and digested to quantify MP. In-depth microscopy analyses were carried out to evaluate potential chemical and physical alterations of MPs during gut passage. Minimal retention of MPs in fireworm tissues was observed, while faecal pellets contained substantial quantities of micro-PS. Despite most MPs exhibiting negligible chemical changes, they were covered by faecal matter and colonised by bacteria, with minor surface alterations. Our findings provide the first evidence of MP trophic transfer from a filter feeder to a carnivorous polychaete. The rapid excretion of MPs by bearded fireworms gives insights into polychaete-mediated MP fluxes and MP fate in benthic ecosystems.