Seasonal characteristics of microplastics ingested by copepods in Jiaozhou Bay, the Yellow Sea

Microplastics (MPs) are a growing threat to marine biota and ecosystems, and zooplankton are at high risk of ingesting MPs. The seasonal changes in MPs in zooplankton and the key environmental factors influencing the retention of MPs in zooplankton are largely unknown. For the first time, the characteristics of MPs in copepods across four seasons in Jiaozhou Bay. The abundance, shape, size, and chemical composition of the MPs in copepods were investigated, and the relationships between the MP/copepod value and key environmental factors were analyzed. The results revealed a significant seasonal difference in MP/copepod values in Jiaozhou Bay. MP/copepod values were 0.26, 0.23, 0.14 and 0.16 in February, May, August and November, respectively. The MP/copepod value was significantly higher in winter and spring than in summer and significantly higher in the estuarine zone than in other zones. Seawater temperature was negatively correlated with the MP/copepod value. No significant seasonal differences were detected in the characteristics of MPs in copepods in Jiaozhou Bay. The size of MPs in copepods ranged from 90 to 2485 μm, with an average of 454 ± 376 μm. Fiber MPs were the most risky to copepods, accounting for 92% of the total ingested MPs. In terms of the chemical composition of the MPs, a total of 11 polymers were detected in copepods in Jiaozhou Bay in the four seasons. The main components were polyester and cellophane (41.9% and 25.7%, respectively). This study provides the key parameters of the MPs in copepods in Jiaozhou Bay and is an important basis for further ecological risk assessments of MPs. The chronic effects of low-level MP retention on copepods, the impact of fibers on copepods, and appropriate assessments of MP risk under different environmental conditions are recommended as research topics for the next step toward developing an environmentally relevant MP risk assessment. THE MAIN FINDING: The seasonal characteristics of microplastics ingested by copepods in Jiaozhou Bay were revealed.