Aged Buoy-derived Microplastics Alter Photosynthetic Performance and Metabolic Regulation in Pyropia yezoensis without Short-term Growth Inhibition.

Plastic aquaculture equipment can release microplastics into seaweed mariculture zones, yet the effects of these particles on cultivated macroalgae remain poorly understood. In this study, Pyropia yezoensis thalli were exposed to field-aged buoy-derived polyvinyl chloride (PVC) and polyethylene terephthalate (PET) microplastics at 0.1, 1, and 10 mg/L for 7 d. Relative growth rate was not significantly affected, whereas other sublethal endpoints showed polymer-specific changes. PVC exposure was associated with stronger lipid peroxidation, carbohydrate depletion at high concentration, and increasing integrated stress. PET exposure mainly induced protein accumulation and peroxidase-related antioxidant responses, with the highest integrated deviation occurring at the lowest concentration. Metabolomic profiling further supported these physiological patterns. PVC-related metabolic changes were mainly associated with antioxidant regulation, lipid metabolism, and pigment-related pathways, consistent with membrane oxidative damage and phycobiliprotein disturbance. PET-related changes were more closely linked to protein synthesis, transport regulation, and cofactor-dependent antioxidant processes. Overall, aged PVC and PET microplastics induced distinct sublethal responses in P. yezoensis, highlighting the need to consider polymer identity, aging status, and combined biomarker-metabolomic endpoints in ecological risk assessment of seaweed mariculture systems.