Distribution characteristics of microplastics and corresponding feeding habits of the dominant shrimps in the rivers of Chongming Island

There is increasing global concern regarding microplastics. Rivers play a key role in the transportation and storage of microplastics on the Earth's surface. Here, we aimed to investigate the spatial-temporal variations in the distribution of microplastics in water as well as in the dominant species of the macrobenthic fauna Exopalaemon modestus and Macrobrachium nipponense in the river system of Chongming Island by setting up 16 fixed sampling sites. We found that the abundance of microplastics in the water of the rivers on the Chongming Island was 0.48 ± 0.10 n/L. There was no significant difference among different reaches. The abundance of microplastics in the major rivers was significantly higher in summer than in the other seasons. Detection rates of microplastics in Exopalaemon modestus and Macrobrachium nipponense were 50.12 % and 64.58 %, with mean abundances of 1.92 ± 0.52 n/g and 1.49 ± 0.30 n/g, respectively. The composition characteristics of the microplastics in shrimps were affected by the microplastics in the aquatic environment. The microplastic content in the shrimps and water were linearly correlated in terms of the same characteristics (shape, color, and polymer). Shrimps showed a stronger feeding preference {Target Group Index (TGI) > 1} for microplastics with fibrous shapes, transparent and green colors, rayon (RA) and polyethylene (PE) polymers, and relatively small sizes (<400 μm). These results indicate that shrimps prefer to consume microplastics that have similar appearance to their prey. Their benthic dwelling habits may limit their feeding space to the bottom of the water, which in turn leads to an increase in the feeding probability on microplastics of greater densities (e.g., RA). The catabolism of microplastics in shrimps may lead to an overestimation of their feeding preference for smaller sizes. Further controlled experiments should be carried out to obtain deeper insights into the preferences of shrimp for microplastics.