MICROPLASTIC IN THE ESTUARINE FOOD WEB OF CHARLESTON HARBOR, SC
Payton, Tokea Gabrielle
Marine organisms including zooplankton to birds forage at flood tide frontal aggregation zones which accumulate semi-buoyant particulates and phytoplankton in Charleston Harbor, SC. Increased trophodynamics and the potential for the accumulation of microplastic particles, which are semi-buoyant particulates, indicate that aggregation zones in the Ashley and Cooper Rivers may present a pathway of increased exposure for microplastic to enter the estuarine trophic system via ingestion by zooplankton. In the present study, fluorescence and bright-field microscopy were used to quantify microplastic concentrations in the top meter of the water column, the gut of zooplankton, and gastrointestinal tracts of fishes. Melting point analysis was used as a secondary identification method. Quantifications of microplastic from water samples collected at the Cooper River front, showed significantly higher concentrations on the riverside and within the frontal zone versus the seaward side (p = 0.0016) indicating an input of microplastic from land based sources. No accumulation of microplastic particles were detected in the Ashley River frontal zone (p = 0.98). Examinations of suspension feeding zooplankton collected in and around flood tidal fronts indicated a significant increase in abundance in the Ashley River front, but not in the Cooper River. In addition, approximately 1% of the zooplankton observed contained ingested microplastic particles. Quantifications of microplastic found in the intestines of local fish species collected from the Charleston Harbor indicated that primary and secondary consumer fishes contain more microplastic per gram weight of fish than top carnivore fishes (p = 8.74 x 10<sup>-5</sup>). With an average of 13 particles per fish, with higher concentrations found in omnivorous fishes, and only 1% of zooplankton containing microplastic, it is suggested that zooplankton may not be as prominent of a pathway for the movement of microplastic into the estuarine food web and transport may derive primarily from the benthic community.