in oligotrophic systems 10^8 - in highly productive environments >10^11 virus particles/litre
||Jover LF, Effler TC, Buchan A, Wilhelm SW, Weitz JS. The elemental composition of virus particles: implications for marine biogeochemical cycles. Nat Rev Microbiol. 2014 Jul12(7):519-28. doi: 10.1038/nrmicro3289. p.524 left column bottom paragraphPubMed ID24931044
|| Clasen, J. L. et al. Evidence that viral abundance across oceans and lakes is driven by different biological factors. Freshw. Biol. 53, 1090–1100 (2008). DOI: 10.1111/j.1365-2427.2008.01992.x link  Wilhelm, S. W. & Matteson, A. R. Freshwater and marine virioplankton: a brief overview of commonalities and differences. Freshw. Biol. 53, 1076–1089 (2008). DOI: 10.1111/j.1365-2427.2008.01980.x link  Danovaro, R. et al. Marine viruses and global climate change. FEMS Microbiol. Rev.35, 993–1034 (2011). doi: 10.1111/j.1574-6976.2010.00258.x. PubMed ID21204862
||Primary source  summary:"Samples from 16 lakes in central (n = 145) and western (n = 12) North America, the coastal northeast Pacific (n = 302) and the western Canadian Arctic Oceans (n = 142) were collected and analysed for viral, bacterial and cyanobacterial abundances and chlorophyll-a concentration."
||P.524 left column bottom paragraph: "Marine virus particles and elemental reservoirs: The total abundance of elements in marine viruses is a product of the abundance of viruses and their per-particle elemental content, both of which can vary across space and time. Marine virus densities range from 10^8 virus particles per litre in oligotrophic systems to more than 10^11 virus particles per litre in highly productive environments [primary sources]. Viruses (in general) and marine viruses (in particular) can vary substantially in genome length and particle size and, consequently, in elemental content (Fig. 2 Supplementary information S1 (box)). However, to extrapolate from particle-scale results to the population scale, variation in the sizes of marine virus particles must be taken into account."