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Ecosystems are driven by primary production. Marine bacteria respire on a daily basis, an amount of organic matter equivalent to about half the total marine primary production. Viruses are thought responsible for c.a. 10~50% of the total bacterial mortality in surface seawater. The viral shunt hypothesis suggested that the viral-lysis process lessened the transfer of bacterial cells to protozoans; and that the lysate released from the broken cells stimulated the growth of the existing bacteria. This viral shunt hypothesis is crucial for microbial biogeochemistry but its applicability to the real world has not been well documented for almost three decades. We suspected that that the timescale adopted in sampling and system trophic status determine the “visibility” of the viral shunt in the field.

The research team of Research Fellow Fuh-Kwo Shiah  at the Research Center for Environmental Changes, Academia Sinica, analyzed a 2010-2017 data set taken from a time-series station (SEATS; 18°N, 116°E) in the tropical South China Sea, and found that bacteria are in famine status in this oligotrophic ocean. The supply of labile substances such as the lysate from viral lysis process stimulates bacteria to turnover in a time-scale of hours. The difficulty of detecting the viral shunt in mesotrophic/eutrophic systems might due to their abundant allochthonous and autochthonous organics input sources. This research has been published in Science Advances on October 12^th, 2022.