Dynamics of microplastic transfer through the food web in a migratory seabird

Estuaries function as sinks for microplastics due to their proximity to urban areas and pollution sources. Because of the great availability of plastic debris in these areas, these pollutants can be accumulated in biota and transferred through the food web. This study aims to examine the dynamics of microplastic trophic transfer in a piscivore seabird species, the Common tern (Sterna hirundo) by analyzing microplastics in spontaneously regurgitated prey throughout the non-breeding season. A total of 120 Argentinian anchovies recovered from spontaneous regurgitates (n = 39) were analyzed, and 81 microplastics fibers were found. The mean length of these fibers was 1.788 ± 1.68 mm. The occurrence of microplastics varied throughout the season, with higher levels observed during the initial months when both Common terns and their prey feed over estuarine waters. Specifically, December showed a higher microplastic concentration in regurgitated fish, thereby increasing the exposure level to microplastics in seabirds. Different colored microplastics were recovered, including black, blue, red, transparent, and green fibers, with monthly variations in their occurrence. Among the identified polymers, polyethylene and cellulose were the most abundant throughout the season. Furthermore, monthly variations in precipitation and population density are associated with microplastic abundance and thus affecting the exposure to microplastics by fish and seabirds. Our results suggest that the dynamics of trophic transfer are related to the feeding behavior and trophic relationships between the studied species, as well as environmental parameters.