Investigating a probable relationship between the distribution of microplastics and crab burrows in the intertidal zone of Chongming Island, Yangtze Estuary.

Crab burrows are common biogeomorphic structures in the sedimentary environment of the intertidal zone. Existing studies have revealed crab burrows could function as traps and sinks for fine sediment particles and organic detritus transported by the overlying water. However, it was unknown whether the distribution of microplastics was related to crab burrows. To build on past work, we investigated the distribution characteristics of microplastics and crab burrows in the intertidal zone of Chongming Island and explored the probable relationship between them. The detection rate and abundance of microplastics in burrows were higher than in no-burrowing areas, indicating that crab burrow have a trapping function for microplastics. Crab burrows also increased the abundance and detection rate of microplastics in the deeper sediment layer, rather than just the surface layer. Furthermore, microplastics were more abundant in large burrows than in small burrows. The microplastics in the large burrow were significantly smaller in size than those in the small burrows and no-burrowing area. The abundance of microplastics positively correlated with the area occupied by burrows in the majority of study sites. Our findings provide a new perspective for exploring the transport and migration of the microplastics between the sediment and water column in the intertidal zone. Further controlled experiments should be carried to investigate the source-sink effects of crab bioturbation in the intertidal flat on microplastics.