Impacts of expanded polystyrene microplastics on gut physiology of a sea slater Ligia cinerascens using multi-omics and stable isotope analyses

Microplastics (MPs) are an increasing concern in coastal environments due to their widespread occurrence and increasing use, with expanded polystyrene (EPS) representing a major plastic pollutant in these ecosystems. Although adverse effects of MPs have been reported across taxa, their biological effects in coastal invertebrates remain insufficiently characterized. Here, we examined the effects of 30-day exposure to EPS MPs on the gut transcriptome and gut microbiota of the coastal sea slater Ligia cinerascens, a dominant detritivorous isopod in rocky shore ecosystems. Gut transcriptomic profiling and 16S rRNA gene sequencing showed limited responses to EPS MP, with only a small number of differentially expressed genes and no significant changes in overall microbial diversity or community structure. Consumption assays indicated that L. cinerascens can ingest EPS MPs, under food-associated conditions, and fragmented particles were detected in the digestive tract and feces. However, stable isotope analysis of hepatopancreas and muscle tissues suggested that ingested EPS was neither metabolically assimilated nor used as an energy source. Collectively, these findings demonstrate that EPS particles can be physically processed during feeding and provide insight into species-specific and limited gut-level responses to MP exposure in a coastal detritivore.