Regulation and response of heterotrophic bacterial production to environmental changes in marginal seas of the Western Pacific Ocean

Heterotrophic bacterial production represents an important part of microbial food web processes in marine ecosystems and plays a significant role in biogeochemical carbon cycle. As environmental factors have changed in marginal seas of the Western Pacific Ocean over the past 20 years, the response and regulation of bacterial production remain poorly understood. In this study, we quantified bacterial production rates using the 3H-leucine incorporation method and investigated the factors influencing bacterial production distributions in the East China Sea and the Yellow Sea. Our data revealed that bacterial production varied largely (1.6–24.4 mg C m−3 d−1) in the surface waters, and higher rates were observed at temperate sites in the East China Sea. Incubation experiments under different temperature or nutrient conditions demonstrated that elevated temperature or the addition of silicate, DIN and phosphate could simulate heterotrophic activity. The decadal increases of BP could be a result of microbial response to the variations in temperature, nutrient levels, and dissolved oxygen that are closely linked to food-web dynamics and biogeochemical processes. High ratios of integrated bacterial production to primary production suggested bacterial production could be supported by non-phytoplanktonic carbon sources, while the low bacterial growth efficiency indicated that a large fraction of carbon was respired in the offshore waters. These results provided insights into the regulations of BP and heterotrophic response to environmental evolution in marginal seas of the Western Pacific Ocean.