Distribution and diversity of microplastics along the aquatic food web in the largest mangrove reserve of China

Knowledge of microplastics (MPs) in consumers at different trophic levels and with different feeding strategies in mangroves is essential to evaluate pathways and ecological effects from exposure to MPs. We conducted a comprehensive study on the distribution of MPs along the food web in the largest natural mangrove reserve in China, and applied diversity index of MPs, D'(MP), in terms of color, size, shape and type, to investigate complexity of MPs through the trophic cascades. The highest abundance of total MPs occurred at 5.7 ± 2.6 items/individual in fish, followed by 4.8 ± 1.9, 3.2 ± 0.5, 2.2 ± 0.9 items/individual in crabs, bivalves and shrimps, respectively. There was a correlation between the abundance of MPs in the gastrointestinal tracts (GITs) or soft tissues of organisms and trophic levels (r = 0.47, p < 0.01), while microplastic abundance were also correlated with body wet weights. The abundance and diversity of MPs in mangrove organisms were influenced by their feeding behaviors and living habitats, as consumers through indirect ingestion had significantly higher abundance of MPs than discriminate feeders. For MPs in their GITs, crabs had the highest shape D'(MP), but the lowest size D'(MP) and color D'(MP), while fish had highest color D'(MP), but significantly lower shape D'(MP). Our application of diversity index of MPs to mangrove ecosystem for the first time reveals a rather complicated distribution of MPs along the aquatic food web, demonstrating an urgent need for measures to reduce the discharge of MPs into mangrove and develop a remediation strategy.