Sam Schwartz

As one of the most prolific photosynthetic organisms in the ocean, the cyanobacterium Synechoccocus play a vital, but little understood role in the transfer of carbon from the atmosphere to the deep sea through a set of processes known collectively as the biological carbon pump (BCP). Carbon dioxide is converted into cells via photosynthesis, and ultimately sinks to the ocean interior as phytodetrital aggregates, thereby sequestering carbon from the atmosphere for thousands of years and reducing climate warming. The impact of predators such as viruses and single celled zooplankton upon Synechococcus conversion into sinking particulate organic carbon (POC) and its export to the deep ocean is unknown. Using cultured model systems, we investigated the impact of viral infection (phage S-SSM5) and zooplankton grazing (dinoflagellate Oxyhrris marina CCMP3375) on the formation of Synechoccocus (WH8102) cellular aggregates and found that combined predation by both viruses and zooplankton resulted in the formation of large (>500µm2) aggregates not observed in other treatments. We also examined whether viral infection influences feeding by the zooplankton upon Synechoccocus. Our simplified food web experiments revealed that viruses reduce the percent of protists mediated upon the cyanobacteria (with virus 39% ± 6%; without virus 68% ± 11%). Our data suggest that viral infection reduces zooplankton feeding upward trophic transfer of Synechoccocus and enhances formation of large cell aggregates. This work highlights the underrepresented role of marine viruses in enhancing large particle formation and the efficiency of the biological carbon pump, potentially reducing the rate of climate change.