Microplastic Abundances in Co-Occurring Marine Mussels: Species and Spatial Differences

Microplastics in marine ecosystems are ingested by a range of organisms. Bivalves are particularly susceptible to microplastic ingestion as they filter large volumes of water for feeding. Many investigations have focussed on commercially important species, with little research investigating other ecosystem engineering species. Here, microplastics in three co-existing mussel species Brachidontes variabilis, Perna viridis, and Xenostrobus securis were examined at four sites in Hong Kong. Microplastic abundance was greater within P. viridis compared to both other species. Average abundances of microplastics observed per individual mussel were 0.2–0.7 ind −1 for B. variabilis, 2.8–14.7​ ind −1 for P. viridis, and 0.6–3.1 ind −1 for X. securis, and when standardised to flesh weight were 0.9–3.1 g −1 for B. variabilis, 2.4–15.1 g −1 for P. viridis, and 1.5–8.4 g −1 for X. securis. Microplastic abundance within mussels was also significantly different among the sites sampled. Over 90% of observed microplastics were fibres, and the colour of microplastics were either red (67%), colourless (16%), blue (9%), or black (6%). The proportion of the microplastic colours found differed among species and sites. This is the first observation of microplastics within B. variabilis and X. securis. By confirming the presence of microplastics within these ecologically important ecosystem engineering species, we suggest that further research be conducted to understand the potential impacts of microplastic ingestion. Further, future microplastic impact investigations should incorporate exposures to microplastic fibres, owing to the high proportion observed within mussels here, and that their presence may lead to damaging effects on the functioning of economically and ecologically important bivalve species.