Modeling the Vertical Transport of Copepod Fecal Particles under Nano/Microplastic Exposure

Nano- and microplastics (NMPs) may significantly impact the marine carbon cycle, and fecal pellets produced by the copepods are crucial for vertical carbon transport. In this study, we investigated the effects of NMP size, concentration, and diatom supply on the production and settling of fecal pellets by the marine copepod Parvocalanus crassirostris. By employing an aggregation-induced emission fluorescence imaging technique, we visualized the distribution of NMPs in fecal pellets, measured their size and production rate, and developed a fluid dynamic model to simulate the settling process of fecal pellets in the water column. Our results indicated that NPs and MPs exhibited uniform and nonuniform distributions in the produced fecal materials, respectively. NMPs reduced both the size and integrity of copepod fecal pellets. Copepods ingested MPs in the absence of diatoms, but exposure to 5000 μg/L of NMPs decreased the fecal pellet production by 52% in the presence of diatoms due to feeding selectivity. The sinking rates of fecal pellets of varying sizes, as obtained from modeling simulations, ranged from 10.9 to 103.1 m/day. When the proportion of participating polystyrene (PS) reached 50%, the sinking velocity decreased by 34%. Our study provides new insights into the vertical transport of copepod fecal pellets under NMP pollution.