Marine debris in salt marshes and microplastic ingestion by Uca pugilator

Marine debris is a direct anthropogenic impact on our ocean ecosystems. Debris is found in various marine ecosystems including the open ocean, seafloor and along coastlines, including estuarine ecosystems. There is limited scientific knowledge of the distribution and impacts of marine debris, particularly in salt marsh habitats. This research sought to: (1) understand factors controlling the presence, accumulation, and distribution of debris found in four North Carolina salt marshes; and (2) assess the incorporation of marine debris into estuarine food webs via Uca pugilator (sand fiddler crab) ingestion of plastic microbeads. From seven debris surveys, 378 items were collected; plastic was the most common debris-type (45%). Debris accumulated as quickly in marshes, with preliminary data showing debris accumulation rates of 7000 debris items / km 2 in 5 months. Debris distribution was positively correlated with a vegetation index that combined shoot height and density, indicating that vegetation likely aids in trapping and retaining debris. Plastic debris is of particular concern due to its tendency to deteriorate into microplastics, which alone can be toxic and can serve as vectors introducing additional toxins into coastal food webs. In a mesocosm experiment, I found a positive correlation between microplastic dosage and the abundance of 330 um microplastics ingested by both male and female fiddler crabs, in 24- and 48-hr trials. My findings suggest that plastics, with their toxins, can readily enter salt marsh food webs and thus, theoretically, bioaccumulate in estuarine ecosystems.