Examining the trophic transfer of plastic-related pollutants to the endangered Hawaiian monk seal in the Northwestern Hawaiian Island marine ecosystem

Microplastics, and their associated chemicals, are widely documented in marine ecosystems, and may biomagnify through the food web and present health risks to top predators. Plastics contain harmful additives (plasticizers) and are known to accumulate harmful contaminants, including persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), which can affect fecundity and immune and endocrine health. Although the Northwestern Hawaiian Islands are far-removed from human activities, plastic debris accumulates there from gyre transport and seabird deposition. An area of particular concern is the atoll of French Frigate Shoals (FFS), which is designated critical habitat for the largest breeding colonies of the endangered Hawaiian monk seal, Monachus schauinslandi, and samples have shown the presence of PCBs in these seals. In addition to plastic debris exposure, previous U.S. government activities in FFS have resulted in significant hazardous material pollution which has been documented to have leached into the marine ecosystem. To evaluate potential pathways of these contaminants into animal tissues around FFS, we constructed an extensive food web and contaminant pathway model. First, we conducted a comprehensive review of the available literature on the diet and feeding ecology of M. schauinslandi and the trophic ecology of identified primary prey components using multiple method sources, including fatty acid and stable isotope analysis, and stomach and scat contents. With compiled data we constructed an ecosystem model of FFS with Ecopath, a widely-used ecosystem modelling software. We then incorporated a contaminant model add-on (Ecotracer) to integrate contaminant exposure pathways through the food web and investigate potential bioaccumulation mechanisms. Our Ecopath with Ecotracer ecosystem model runs simulate the trophic transfer of plastic-related contaminants, both additives and sorbed chemicals, through parameterized feeding interactions.