High Microplastic Contamination in Juvenile Tri-Spine Horseshoe Crabs : A Baseline Study of Nursery Habitats in Northern Beibu Gulf, China

Microplastics (MPs) are ubiquitous in marine sedimentary environments. Their occurrence in horseshoe crabs and interactions with the sedimentary environment has not been determined. In this study, MPs, mostly microfibers, were found in all extracted gastrointestinal tract (GIT) samples of the juvenile Tachypleus tridentatus from the northern Beibu Gulf, China. The MP concentrations (4–53 items ind⁻¹) were higher than those in most marine benthic invertebrates (< 15 items ind⁻¹) reported in Chinese waters, despite their generally low level in habitat sediments (9-1818 items kg⁻¹). The correlation between the juveniles and sediments was not evident, but the abundance in juvenile horseshoe crab GITs decreased with ages. The findings were relevant to the life-history characteristics of the species, typically with limited dispersal capability and their spending nine years or longer time living in mangrove wetlands during low tides, with apparent ontogenetic changes in their diets. These baseline data enable a better understanding of MP availability in benthic macroinvertebrates, and the ecological risks present in the ecosystems.