Use of estuarine resources by top predator fishes. How do ecological patterns affect rates of contamination by microplastics?

This study assessed the seasonal patterns of habitat utilization, feeding ecology and microplastic contamination in different ontogenetic phases of sympatric snooks (Centropomus undecimalis and C. mexicanus) inhabiting a tropical estuary. More than 50% of snooks, in all ontogenetic phases, ingested microplastics (1.5 ± 0.1 and 1.4 ± 0.1 particles ind). Juveniles migrated to nursery grounds in the upper estuary, during the early dry (C. undecimalis 6.5 ± 2.8 ind) (p < 0.01) and early rainy seasons (C. mexicanus 4.1 ± 1.9 ind). There, they fed mostly on invertebrates (Polychaeta) (p < 0.01), and became contaminated by microplastics (C. undecimalis: 0.8 ± 0.4 particles ind; C. mexicanus: 1.7 ± 0.5 particles ind). Sub-adults of both species forage principally in the estuarine habitats after shifting their diet from invertebrates (shrimps) in the upper reaches (1806.4 ± 1729.6 mg ind) to pelagic fishes (R. bahiensis) in seaward habitats (2507.7 ± 1758.4 mg ind). During feeding continues the contamination by microplastics (3.1 ± 0.8 part. ind). Adults use the adjacent coastal as feeding and spawning grounds during the rainy season. In this phase, snooks are mostly piscivorous (R. bahiensis: up to 5303.8 ± 3213.4 mg ind), but also ingest penaeid shrimp as complementary item (up to 175.9 ± 156.7). Microplastics contamination rates increased towards the adult phase, with maximum contamination coinciding with peaks of fish ingestion, suggesting trophic transfer of microplastics. The lower estuary and adjacent coastal zone were important contamination sites, especially during the rainy season (up to 3.1 ± 0.8 part. ind) (p < 0.01), when fishery activities is intense and river basin runoff increases. Consequently, the availability of microplastics is higher during this time of year in the lower portion of the estuary. Snooks had similar prey preferences, but the use of different habitats along the life cycle of each species avoids overlaps in estuarine use and minimizes competition.