Microplastics in Macomona liliana: A Study of Bioaccumulation and Influencing Environmental Factors

Microplastic contamination in coastal ecosystems threatens benthic communities, yet quantitative tissue contamination data for ecologically important species remain scarce, particularly for endemic fauna in Southern Hemisphere coastal systems. This study addressed critical knowledge gaps by investigating microplastic presence, polymer composition, and environmental drivers of contamination in Macomona liliana, an endemic New Zealand bivalve that serves as both an ecosystem engineer and primary prey for protected shorebird populations. Field sampling across ten stations in Manukau Harbour examined spatial variation in contamination patterns. Specimens were analysed using pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) for quantitative polymer identification, with the highest confidence in polypropylene measurements. Sediment characteristics were measured to assess potential drivers of tissue microplastic concentration patterns. Microplastic contamination was detected in all M. liliana specimens (n=57), with tissue concentrations ranging from 621.67 to 2353.60 μg/g dry weight. Polymer composition was dominated by polystyrene (49.4% by mass), followed by polyethylene terephthalate (38.0%), polyvinyl chloride (7.0%), and polypropylene (5.6%). Principal component analysis showed that sediment characteristics explained 81.3% variance in contamination patterns, indicating complex, multifactorial control mechanisms. This research provides the first quantitative assessment of microplastic tissue contamination in wild M. liliana populations, despite analytical challenges in biological matrices, and it establishes a foundation for mass-based analytical protocols for ongoing monitoring. These findings contribute essential baseline data for New Zealand coastal ecosystems with implications for protected species management.