Microplastic accumulation via trophic transfer: Can a predatory crab counter the adverse effects of microplastics by body defence?

Microplastics are considered detrimental to aquatic organisms due to their potential accumulation along food chains. Thus, it is puzzling why some of them appear unaffected by microplastics. Here, we assessed the contribution of water filtration and food consumption to microplastic accumulation in a predatory marine crab (Charybdis japonica) and examined the associated impacts of microplastics (particle size: 5 μm) following ingestion for one week. Results showed that water filtration and food consumption contributed similarly to the accumulation of microplastics, which were distributed among organs in this order: hepatopancreas > guts > gills > muscles. Yet, biomagnification (i.e. accumulation through consumption of microplastic-contaminated mussels) did not occur possibly due to egestion of microplastics. The crabs upregulated detoxification capacity (EROD) and antioxidant defence (GST) in response to the microplastics accumulated in their tissues. However, these defence mechanisms collapsed when the microplastic concentration in hepatopancreas exceeded ~3 mg g, leading to severe hepatic injury (elevated AST and ALT) and impaired neural activity (reduced AChE). Our results suggest that marine organisms have an innate capacity to counter the acute effects of microplastics, but there is a limit beyond which the defence mechanisms fail and hence physiological functions are impaired. As microplastic pollution will deteriorate in the future, the fitness and survival of marine organisms may be undermined by microplastics, affecting the stability and functioning of marine ecosystems.