Key factors regulating springtime phytoplankton primary production in the coastal waters of South Korea

Phytoplankton primary production is fundamental to marine ecosystems, serving as the foundation of the ecological pyramid. However, little information is currently available on the primary production in coastal waters of South Korea. To address this knowledge gap, primary production was measured using a ¹³C stable isotope tracer in May 2022 and 2023. The mean daily primary production during the observation period were 403.5 ± 317.8 mg C m⁻² d⁻¹ in the coastal Yellow Sea (YS), 722.0 ± 464.6 mg C m⁻² d⁻¹ in the coastal East Sea (ES), and 739.8 ± 594.1 mg C m⁻² d⁻¹ in the coastal South Sea (SS), respectively. In the coastal YS, northern stations, including the Geum River estuary, showed significantly higher primary production than southern stations (Mann-Whitney U test, p < 0.05), with station W44 exhibiting an exceptionally high value among the southern stations. Similarly, notable regional variation was observed in the coastal SS, where the primary production in the eastern region was approximately 6-fold higher then the western region (Mann-Whitney U test, p < 0.05). Principal component analysis (PCA) and multiple linear regression (MLR) identified chlorophyll a concentration and light intensity as the key factors regulating the primary production across the regions. These findings highlight the critical role of these factors in shaping productivity patterns and underscore the need for ongoing monitoring of primary production to further enhance understanding of coastal ecosystems in South Korea.