Experimental assessment of microplastic selectivity in the brown mussel Perna perna (Linnaeus, 1758)

Abstract

Microplastics are ubiquitous in aquatic ecosystems and raise concerns due to their persistence and potential toxicity. Given their known impacts on marine species and the use of bivalves as sentinel species for contamination monitoring, this study aimed to experimentally investigate the selectivity of the brown mussel Perna perna (Linnaeus, 1758) when exposed to the chlorophyte microalga Tetraselmis sp. F. Stein, 1878 and plastic microbeads of similar morphology and size. The study hypothesis is that when microplastics resemble natural food in shape and size, P. perna can discriminate between particles, preferentially ingesting microalgae and rejecting microplastics. Experiments included three treatments in triplicate: microalgae only (MA), polystyrene microbeads only (MB), and a 1:1 mixture of microalgae and polystyrene microbeads (MA+MB). Aliquots were collected at the beginning and end of the incubation period and quantified using an optical microscope. Clearance and ingestion rates were calculated for each replicate, and mean values were determined. Although ingestion rates did not differ significantly among treatments, the clearance rate was significantly higher in the MB treatment (627.07 mL g dw-1 h-1) than in MA (270.59 mL g dw-1 h-1) and MA+MB (518.39 mL g dw-1 h-1), suggesting increased filtering activity. Ingestion rates ranged from 6.80 x 104 to 1.22 x 105 particles g dw-1 h-1 across treatments. Mussels ingested microbeads regardless of microalgal availability, indicating no particle selectivity. Hence, the study hypothesis was not supported. Ecologically, this inability to discriminate among particles may have detrimental consequences for mussels. A similar pattern may occur in natural environments, where microplastics are present in the water column of coastal areas and interact with plankton and suspended organic particles, facilitating ingestion and subsequent contamination.