Assessment of juvenile mussel growth and health following chronic exposure to anthropogenic fibres

, Walkinshaw Chris, Cole Matthew, Tolhurst Trevor, Lindeque Penelope, Thompson Richard.

Mussels are considered a valuable model species for investigating microplastic toxicity, however the majority of existing studies have focussed upon the adult life stage. Here, a chronic exposure experiment was undertaken to investigate the effect of anthropogenic microfibres (polyester or cotton) on juvenile mussels (Mytilus spp.). Juveniles were chosen for this study as effects of microfibers on juveniles are currently under-represented, and early life stages are more sensitive to external stressors. Fibres were manufactured by cryo-grinding to represent a range of sizes commonly found in the marine environment (average polyester length = 293µm, average cotton fibre length = 171µm), and represent some of the most prevalent fibres found in oceans worldwide. Mussels (5 individuals per beaker) were maintained in 1 L glass beakers, with a continuous flow-through of algae-enriched filtered natural seawater under controlled laboratory conditions. Mussel cohorts were exposed to one of four experimental conditions over a three-month exposure period: (1) control (algae only; n=5); (2) cotton microfibres (100 per L; n=5); (3) low microplastic concentration (10 per L; n=5); (4) high microplastic concentration (100 per L; n=5). Condition (3) simulates current marine microplastic levels, with condition (4) simulating theoretic future concentrations. Algal clearance rate, shell length and oxygen consumption rate were monitored to assess how prolonged exposure to anthropogenic fibres might affect mussel feeding, growth and metabolic rate. Scope for growth was calculated at the end of the exposure period. Further, mussels were KOH digested to quantify anthropogenic fibre ingestion. Understanding the effect of microfiber ingestion on feeding, growth and respiration in juvenile organisms is critical to understanding the effect of microplastic pollution to the value of commercially exploited marine species. Our results provide insight into how environmentally relevant concentrations of plastic and cotton microfibers have the potential to affect feeding and growth of commercially valuable bivalve shellfish.

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