Smaller fibrous microplastics exert stronger multi-level effects on the intertidal mud crab (Macrophthalmus japonicus)

Microplastics (MPs) are widespread in aquatic environments, with fibrous MPs (f_MPs) particularly dominant in both marine and freshwater ecosystems. This study examined the multi-level effects of exposure to f_MPs on the intertidal mud crab ( Macrophthalmus japonicus ). The survival rate declined more significantly following exposure to small f_MPs (sf_MPs) than to large f_MPs (lf_MPs). The gills accumulated more f_MPs than the hepatopancreas and stomach, while bioaccumulation levels were generally higher for sf_MPs than for lf_MPs. The accumulation of sf_MPs was highest after seven days of exposure for all tissues, whereas accumulation of lf_MPs was highest after four days in the gills and stomach. Morphological changes in the f_MPs were observed within crab tissues following uptake. It was also found that f_MP exposure changed the surface roughness of the exoskeleton, induced histological damage in the gills, increased the activity of antioxidant enzymes, altered the expression patterns of innate immune-related genes, and raised global DNA methylation levels. Overall, sf_MPs exhibited a greater toxic effect than lf_MPs. These findings highlight the environmental risks associated with f_MP exposure in benthic crustaceans such as M. japonicus , which are important indicators of the health of the food web and the safety of seafood for human consumption.