Microplastics in copepods reflects the manmade flow restrictions in the Kochi backwaters, along the southwest coast of India.

This baseline study on microplastics (MPs) in calanoid copepods in the Kochi backwaters (KBW), India's largest estuary system on the west coast, focuses on (a) the spatiotemporal variations of MPs with the seasonal hydrography setting, and (b) how man-made flow restrictions of a large saltwater barrage contribute to MPs in copepods and their potential to transfer to higher trophic levels. This study found that MPs in copepods in the KBW ranged from av. 0.01 ± 0.014 to 0.11 ± 0.03 no./ind. seasonally. When the saltwater barrage shutters were fully/partially closed during the Pre-monsoon/Northeast Monsoon, MPs in copepods were considerably larger (av. 0.11 ± 0.03 no./ind., and av. 0.075 ± 0.02 no./ind., respectively) as compared to the Southwest Monsoon (av. 0.03 ± 0.01 no./ind.), when the barrage shutters were fully open. This shows the potential of man-made flow restrictions to increase the bioconcentration of MPs in copepods and their possible transfer to higher trophic levels through the food chain, adding to the region's previous discovery that much higher trophic level resources are polluted with a high concentration of MPs. • Seasonal distribution of MPs in copepods in the KBW is presented. • Thanneermukkom barrage (TB) favours the accumulation of MPs in copepods. • Copepods accumulated more MPs during non-monsoon seasons. • MPs accumulated in copepods have the potential to transfer to higher trophic levels. • Periodic open and close of TB is suggested. [ABSTRACT FROM AUTHOR]