Microplastic fibres in juvenile European plaice (Pleuronectes platessa) and Whiting (Merlangius merlangus) from Swansea Bay

Microplastic fibres (MPF), pervasive in marine environments due to their persistent nature and diminutive size, pose ecological threats as potential targets for ingestion by native species. This study contributes to the ongoing data collection effort on MPF prevalence in marine wildlife by investigating MPF presence in the gastrointestinal tract (GIT) of juvenile Pleuronectes platessa (European plaice) and Merlangius merlangus (whiting) fish samples from the Swansea Bay ecosystem. Specimens were collected using beam trawl and their GITs were dissected and probed for MPF presence. Among all analysed specimens, 35.9% contained fibres, with a significantly higher average number of MPF/GIT in the whiting population (49.2% with MPF; 0.92 MPF/GIT) than plaice (21.4% with MPF; 0.29 MPF/GIT). Both fish consume plankton and planktotrophic fish. Plankton are prone to MPF ingestion, attributed to the resemblance of MPF to their natural diet, and so it was hypothesised that trophic transfer of MPF had occurred. Whiting generally consumes a wider variety of planktonic organisms, potentially explaining the elevated MPF prevalence observed in the whiting specimen compared to the plaice. While this research served only as a preliminary study (and thus, potentially confounding factors were not considered), these results demonstrate the presence of microplastics in this Swansea Bay ecosystem and highlight concerns regarding microplastic bioaccumulation and trophic transfer.