Nutritional quality and seasonal variation characteristics of Pyropia haitanensis, an economic seaweed

Pyropia haitanensis is an economically important seaweed that is rich in proteins, polysaccharides, and various medicinal components, and has unique flavor. Although research on P. haitanensis has increased in recent years, relatively few studies have investigated the seasonal dynamics of its key nutritional components. To fill this research gap, monthly sampling was conducted at a coastal P. haitanensis farm in Dongtou District, Wenzhou, China, from November 2024 to January 2025. The results showed that P. haitanensis transitioned physiologically from rapid growth to nutrient accumulation from November 2024 to January 2025. This transition was evidenced by a decline in the daily relative growth rate from 1.19% to 0.68%. Correspondingly, the total amino acid, soluble carbohydrate, and ash contents increased. December represented a critical period for P. haitanensis nitrogen metabolism. During this month, both the nitrogen uptake rate (1.42 ± 0.06 g·g -1 Fw·h -1 ) and nitrogen assimilation rate (0.65 ± 0.04 g·g -1 Fw·h -1 ) reached their annual maximum, and the soluble protein content peaked at 5.79 g/100gDw. Additionally, the photosynthetic pigments concentrations and the expression levels of carbon and nitrogen assimilation metabolic enzymes in P. haitanensis showed coordinated but asynchronous seasonal changes, Photosynthetic pigment concentrations were correlated with light-harvesting efficiency and carbon fixation capacity, while the expression patterns of assimilation enzymes matched the fluctuations in soluble protein and soluble carbohydrate contents. In summary, P. haitanensis redistributes metabolic resources from vegetative growth to nutrient accumulation in the late growth phase, leading to pronounced differences in nutritional quality among thalli harvested in different months.