Does the trophic guild influence microplastic ingestion in nursery areas? A case study on a southwestern Atlantic mangrove-dominated estuary

Mangroves are highly productive ecosystems that serve as critical interfaces between freshwater and marine environments, providing essential habitats for numerous species during early developmental stages. However, these ecosystems face increasing threats from habitat loss and hazardous waste, including microplastics (MPs <5000 μm). This study investigated MP ingestion in ten fish species inhabiting a nursery ground in a mangrove-dominated estuary in the Southwestern Tropical Atlantic. Microplastics were detected in 61 % of the 145 specimens analysed, the polymers consisted primarily of polystyrene and polypropylene (detection limit of 20 μm). The zooplanktivorous species (Atherinella brasiliensis) exhibited the highest ingestion (2.33 ± 1.99 MPs ind; p = 0.0045), influenced by filter-feeding behavior and habitat use in the water column. No correlation was observed between the standard length (ρ = -0.072, p = 0.393) or total weight (ρ = -0.065, p = 0.439) of the specimens with the number of MPs ingested, indicating that ecological factors, are more influential in MP ingestion patterns. Regarding particle size, zooplanktivorous species ingested significantly smaller MPs (501.7 ± 391.9 μm) compared to zoobenthivorous species (802.7 ± 631.0 μm; p = 0.0178). Fibres were the predominant shape detected, reflecting their abundance in the water column. Therefore higher likelihood of ingestion by filter-feeding species. Scanning Electron Microscopy revealed weathered surfaces in the ingested MPs, indicating prolonged environmental exposure and enhanced potential for adsorbing chemical pollutants. These findings highlight mangroves' ecological importance as pollution sinks and underscore the need for conservation efforts and strategies to mitigate plastic contamination in such vulnerable ecosystems.