The role of mangrove crabs, the key macrofaunal bioengineers, in microplastic production in tropical coastal forests

The negative impact of microplastics is evident worldwide, at both an organismal and ecosystem level, representing a global environmental concern. Physical weathering, chemical and microbial degradation are major known primary pathways for secondary microplastic generation. Here, we show another mechanism which plays a role in the formation of microplastics. We demonstrated the ability of mangrove crabs Parasesarma bidens and Metopograpsus quadridentatus to rapidly shred macro-sized foamed plastics into numerous microplastics through their feeding behaviours. The negative buoyancy of produced fragments illustrated their likely result of being deposited in the environment. Furthermore, the production of plastic fragments varied with respect to crab species and the conditions of the plastic, suggesting an association with the foraging and feeding behaviours of the crabs. These results reveal the contributions of macrofauna to microplastic formation, highlighting the importance of taking macrofaunal fragmentation into account when modelling the source and pathways of plastics in the environment. Macrofauna are often dominant bioengineers (e.g. mangrove crabs) maintaining the health of ecosystems, however, they are now expending energy shredding plastic which could otherwise be used for behaviours that benefit ecological functioning. Studying these interactions not only have a utility in both the ecology and functioning of ecosystems but also overall environmental health.