Physiological Responses of Cultured Seaweed Pyropia yezoensis to Phosphorous Limitation in the Nakdong River Estuary, Korea

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Pyropia yezoensis cultured in the estuary of the Nakdong River in Korea is an important fisheries resource for the local economy. Over the past few decades, the environmental conditions of this estuary have undergone marked changes due to coastal development, and particularly so since the construction of weirs in the main stream of the Nakdong River in 2012, which has resulted in changes in seawater nutrient concentrations. Although the production of P. yezoensis has declined notably since 2012, little is known regarding the relationship between this decline and the environmental changes. In this study, during the period from February to March 2017, we investigated environmental parameters and physiological characteristics of the cultured P. yezoensis in the Nakdong River Estuary in order to determine the factors limiting the growth of this macroalga. Water temperature, salinity, and irradiance at estuary sites were found to be favorable for Pyropia culture. High nitrogen (N) and low phosphorus (P) concentrations were measured in the sea water, which has led to a high N:P ratio. Comparable trends were observed in the N, P, and photosynthetic pigment contents of P. yezoensis tissues. Our results indicate that a deficiency in P might be a factor limiting the growth of Pyropia cultured in the Nakdong River Estuary. This study provides valuable information for gaining an understanding of the impact of environmental changes on the production of Pyropia culture in the Nakdong River Estuary.