Microplastic Exposure Pathways in Estuarine Teleost Fishes with Different Feeding Strategies: Importance of What, Where and How you Eat

Coastal high-salinity estuaries in proximity to urban centers have elevated levels of microplastic debris, and ingestion of microplastics by fishes is a common occurrence in these environments. But the composition and quantity of microplastics ingested can greatly vary depending on the feeding strategies of different fish species. Microplastic ingestion can occur through trophic transfer by the consumption of specific prey that have themselves ingested microplastics, or through the direct ingestion of microplastics of similar size to potential prey, commonly through the filtration of water or sediments. To identify the pathways leading to microplastic ingestion in fishes, we compared the microplastic loads in intestinal tracts from seven teleost fishes with different feeding behaviors and trophic levels in Charleston Harbor (South Carolina). Analyzed fishes included benthic and pelagic filter-feeding fishes, benthic invertebrate feeding species, and higher trophic level predatory fish. Specimens of Spot, Leiostomus xanthurus; Striped Killifish, Fundulus majalis; Mummichog, Fundulus heteroclitus; Striped Mullet, Mugil cephalus; Bay Anchovy, Anchoa mitchili; Atlantic Menhaden, Brevoortia tyrannus; and Spotted Seatrout, Cynoscion nebulosus, were collected in Charleston Harbor estuarine waters. Digestive tracts were dissected and digested in 1M KOH and microplastics counted and classified by color and type. Planktivorous fishes had the highest loads of microplastics of all species, containing almost exclusively plastic fibers. Fibers were the most common type of plastic in all species, but plastic fragments, foam and tire wear particles were also abundant in particular fishes. Benthic feeding species with distributions restricted to vegetated marsh habitats had higher ingestion rates of microplastics than those inhabiting nearby sandy environments. Larger predatory species likely ingested microplastics through ingestion of prey, while planktivorous species seemed to ingest fibers directly, possibly aided by the abundance of organic marine snow in the estuarine environment. In-depth spatial and dietary differences between fish species will be discussed in more detail to elucidate potential microplastic trophic pathways in estuarine ecosystems.