Viral decay and viral production rates in continental-shelf and deep-sea sediments of the Mediterranean Sea

Here, for the first time, we have carried out synoptic measurements of viral production and decay rates in continental-shelf and deep-sea sediments of the Mediterranean Sea, to explore the viral balance. The net viral production and decay rates (1.1-61.2 and 0.6-13.5×107 viruses g-1 h-1, respectively) were significantly correlated, and were related also to prokaryotic heterotrophic production. The addition of enzymes increased decay rates in the surface sediments, but not in the subsurface sediments. The viral production and decay rates both decreased significantly in the deeper sediment layers, while the virus-to-prokaryote abundance ratio increased, suggesting a high preservation of viruses in the subsurface sediments. Viral decay did not balance viral production at any of the sites investigated, accounting on average for ca. 32% of the gross viral production in the marine sediments. We estimate that the carbon released by viral decay contributed 6%-23% to the total carbon released by the viral shunt. Since only ca. 2% of the viruses produced can infect other prokaryotes, the majority is not subjected to direct lysis and potentially remains as a food source for benthic consumers. Results reported here suggest that viral decay can play an important role in biogeochemical cycles and benthic tropho-dynamics.