Effects of micro/nanoplastics on physiological and biochemical responses at different life history stages of Neopyropia yezoensis

Micro- and nanoplastics (MNPs) pollution poses significant ecological risks to marine environments and has become a globally recognized environmental concern. As essential primary producers, macroalgae readily adsorb and accumulate these particles, potentially disrupting their physiological processes. However, the effects of MNPs on different life history stages of economically important macroalgae remain poorly understood. In this study, we investigated the effects of polystyrene microplastics (PS-MPs, 1 μm) and nanoplastics (PS-NPs, 80 nm) at varying concentrations (0.02-10 mg/L) on the conchospore germination, seedling growth, and physiological biochemical responses of Neopyropia yezoensis. The results showed that 10 mg/L PS-MPs significantly inhibited early conchospore germination and seedling survival rates, whereas 0.1 mg/L PS-MPs promoted conchospore germination. Although PS-NPs had no significant effect on seedling survival, exposure to 10 mg/L PS-NPs significantly inhibited conchospore germination on the first day of exposure. During the thallus stage, PS-MPs exerted no significant effects on the photosynthesis and respiration of thalli but still induced disruption of cellular structural integrity. In contrast, PS-NPs reduced the relative growth rate and net photosynthetic rate, which may be attributed to decreased contents of phycoerythrin (PE) and phycocyanin (PC). Concurrently, both PS-MPs and PS-NPs increased superoxide dismutase (SOD) and catalase (CAT) activities as well as lipid peroxidation level. Integrated Biomarker Response analysis indicated that PS-NPs generally exhibited higher overall toxicity than PS-MPs at the thallus stage. Collectively, these findings demonstrate that the toxicity of MNPs to N. yezoensis depends on particle size, concentration, and life-history stage. This study provides new perspectives for the ecological risk assessment of MNPs.