Microplastic contamination in Atherinella brasiliensis: Insights into plastic pollution in mangrove ecosystems of the Southwestern Atlantic

Estuaries are acknowledged as the main source of microplastics (MPs; <5 mm) to the ocean. The structure of estuarine ecosystems is strongly modulated by riverine and tidal inflow. Yet, data on MP contamination in estuarine species considering seasonal variability in marine protected areas remain limited. This study analysed the gastrointestinal tract of Atherinella brasiliensis, an abundant species in mangrove-dominated estuaries from the Western Atlantic, to assess the influence of spatial and seasonal variations on MP contamination. A total of 175 MPs, identified as polystyrene, polypropylene and polymethylmethacrylate through Raman spectroscopy analysis, were detected in 111 specimens (Frequency of occurrence = 63 %). The highest MP ingestion was observed during the rainy season (1.95 +/- 2.19 MPs ind.(-1)) (p-value= 0.02), suggesting an increased contaminant input from river runoff. Interestingly, despite the lack of spatial variability (p-value= 0.64), the lowest levels of MP contamination were observed in individuals from Area A during the dry season (p-value= 0.005). Area A, under strong riverine influence, showed greater seasonal variability than Area B, which is more marine-influenced and exhibited no seasonal variation (p-value= 0.72). The widespread occurrence of MPs in A. brasiliensis, coupled with its broad distribution, supports its use as a bioindicator of MP contamination in estuarine surface waters. These findings underscore the vulnerability of mangrove ecosystems to MP pollution, emphasizing the urgent need for monitoring and conservation policies to safeguard these critical habitats.