First Estimation of the Annual Biosynthetic Calorie Production by Phytoplankton in the Yellow Sea, South Sea of Korea, East China Sea, and East Sea

We investigated the spatio-temporal variations in three key biomolecular compounds (carbohydrates, proteins, and lipids) in particulate organic matter (POM) in the Yellow Sea (YS), South Sea of Korea (SS), East China Sea (ECS), and East Sea (Sea of Japan; ES) in order to estimate the regional annual calorie production rates based on the seasonal data obtained in each region. Carbohydrates were found to be most dominant, followed by lipids across all seas. The euphotic-integral calorie contents of POM during the study period were determined as 53.5 ± 12.6 Kcal m−2 in the YS; 54.2 ± 7.5 Kcal m−2 in the SS; 35.7 ± 9.2 Kcal m−2 in the ECS; and 58.7 ± 6.2 Kcal m−2 in the ES. Utilizing seasonal carbon conversion factors and primary production rates, we estimated the annual calorie productions, which were highest in the ES (1705 Kcal m−2 y−1) and lowest in the ECS (403 Kcal m−2 y−1). This can be attributed to the significantly higher energy efficiency of phytoplankton and faster turnover rate of calorie content. However, caution must be taken when comparing these estimates regionally, considering potential variations in developmental phases among the four regions during the sampling period in 2018. The calorie production rates in this study provide valuable insights into the physiological condition of phytoplankton within specific regions.