Mangrove Filters or Microplastic Traps? Insights from Microplastic Ingestion in Polymesoda erosa in Butuan Bay, Philippines

Microplastic pollution threatens ecosystems, particularly in mangrove environments where complex ecological interactions occur. This study investigated the ingestion of microplastics by Polymesoda erosa, a mangrove-dwelling bivalve and evaluated whether mangroves function as natural filters or inadvertent traps for microplastics. A total of 135 specimens were collected from three mangrove sites along a transect in Butuan City, Philippines. Microplastics were extracted from the gastrointestinal tract and characterized by type, color, shape, and polymer composition using stereomicroscopy and ATR-FTIR analysis. The results revealed a prevalence of microplastics across all sites, with fibers being the most dominant shape and blue and black the most frequently observed colors. Statistical analysis using the Kruskal-Wallis test indicated no significant differences (p = 0.787) in microplastic abundance among the sampling sites. Polymer analysis identified polyethylene, polyethylene terephthalate, and ethylene-vinyl acetate among the common materials ingested. These findings suggest that mangroves may serve a dual role: acting as filters that retain microplastics while also becoming traps that expose benthic and filter-feeding organisms to microplastic contamination. However, the study is limited by the small sample size, short sampling duration, and lack of sediment MP analysis, which constrain broader ecological generalizations. Despite these constraints, the findings offer valuable insights into the role of tropical mangrove ecosystems in influencing microplastic bioavailability and microplastic accumulation that may compromise bivalve health, disrupt food webs, and pose potential risks to human consumers. This study highlights the urgent need for improved plastic waste management and further research into the long-term impacts of microplastic exposure in mangrove-associated biota.