Effects of microplastics on the tropical fiddler crab Uca rapax

Nowadays, plastic debris are omnipresent in the oceans and became a major environmental problem over the years. Plastics are fragmentating, yielding microplastics (< 5 mm), which are cunently accumulating in marine sediments posing a risk for deposit feeding inve1iebrates. In a 2-month laboratory experiment, it was tested whether the fiddler crab, Uca rapax, ingests microplastics (polystyrene fragments, 180 - 250 μm) and if the ingestion of these particles affect growth, motility and alter their tolerance to hypoxia. Microplastic paiiicles (108 mg microplastic/kg dry weight sediment) were previously submerged in three different levels of pollution for 14 days (artificial, low pollution, high pollution), mixed with sediment and used in feeding experiments. Additionally, to test a concentration-dependend effect on the same response variables, individuals were exposed to two different concentrations of highly polluted microplastics to mimic present and future microplastic contamination (108 mg and 1000 mg microplastic/kg dry weight sediment). Beside the feeding experiments, microplastic concentrations were quantified in the Itaipu Lagoon, where Uca rapax occurs in high densities. No significant effects of microplastics were found on growth, motility and tolerance to stress. Nevertheless, high concentrations of microplastics caused a clear trend in survival of Uca rapax during hypoxia stress and differences between groups were marginally insignificant. Although, microplastics were found in the stomach, gills and hepatopancreas of the individuals but neither the mere presence of microplastics nor the possible carry-over of pollutants affected the individuals. Due to the presence of these particles in different body parts and in sediment samples of the local habitat of Uca rapax, detrimental long-te1m effects of microplastics on Uca rapax cannot be excluded by this study mostly.