Viral shunt
[7] For his contributions to understanding of viral roles in marine ecosystems, Suttle has received numerous awards, including being named a Fellow of the Royal Society of Canada, receiving the A.G. Huntsman Award for Excellence in Marine Science, and the Timothy R. Parsons Medal for Excellence in Ocean Sciences from the Department of Fisheries and Oceans.
[11] Virologists in soil sciences have begun to investigate the application of viral shunt to explain nutrient recycling in terrestrial systems.
[citation needed] There is evidence to suggest that the viral shunt system can directly control bacterial growth efficiency (BGE) in pelagic regions.
[14] Carbon flow models indicated that decreased BGE could be largely explained by the viral shunt, which caused the conversion of bacterial biomass to DOM.
Data extracted from other aquatic regions such as the Western-North Pacific displayed large variability, which may be a result of methodologies and environmental conditions.
The microbial loop connects the pool of DOM to the rest of the food web, specifically various microorganisms in the water column.
Stratification of the water column due to the pycnocline affects the amount of dissolved carbon in the upper mixing layer, and the mechanisms shows seasonal variation.
When nutrients enter the microbial loop, they tend to remain in the photic zone longer, due to the location, and slow sinking rates of microbes.
This is a very significant process as approximately 3 gigatonnes of carbon may be sequestered per year due to lysed and virus-infected cells having faster sinking rates.
Concurrently, a more efficient biological pump also results in an increase in nutrient influx towards the surface, which is beneficial to primary production, especially in more oligotrophic region.
Export of carbon-rich POM from the upper surface layer to deep oceans causes increased efficiency of the biological pump due to a higher carbon-to-nutrient ratio.
[26] The effect of this energy flow results is less carbon entering higher trophic levels and a significant portion being respired and cycled between the microbes in the water column.
When the viral shunt kills a portion of these microbes, it decreases the amount of carbon that gets transferred to higher trophic levels by converting it back to DOM and POM.
Susceptible microorganisms such as bacteria in the water column are more likely to be infected and killed off by viruses, releasing DOM and nutrients containing carbon and nitrogen (about 4C:1N).
The DOM and nutrients generated from the death and lysis of susceptible microorganisms are available for uptake by virus-resistant eukaryotes and prokaryotes.
A significant fraction of the world's oceans are iron limited,[32] thus the regeneration of iron-nutrients is an important process that is needed for sustaining an ecosystem in this environment.
Viral infection of microorganisms (mostly heterotrophs and cyanobacteria) is hypothesized to be an important process in the maintenance of high-nutrient low chlorophyll (HNLC) marine environments.
[33] The viral shunt plays a key role in releasing assimilated iron back into the microbial loop which helps sustain primary productivity in these ecosystems.
Naturally, this prevents the export of biomass such as POM to higher trophic levels directly, by diverting the flow of carbon and nutrients from all microbial cells into a DOM pool, recycled and ready for uptake.
[37] Viruses that specifically target cyanobacteria known as cyanophages (found in surface waters) directly affects the marine food web by "short-circuiting" the amount of organic carbon that is transferred to higher trophic levels.
[44] Additionally, microbes tend to be pelagic, floating freely in photic surface waters, before sinking down to deeper layers of the ocean.
An increase in these viruses can cause large mortality of vent microbes, thereby reducing chemoautotrophic carbon production, while at the same time enhancing the metabolism of heterotrophs through recycling of DOC.
[46] These results indicate a tight coupling of viruses and primary/secondary production found in these hydrothermal vent communities, as well as having a major effect on the food web energy transfer efficiency to higher trophic levels.
