Abstract
Marine viruses are critical drivers of ocean biogeochemistry, and their abundances vary spatiotemporally in the global oceans, with upper estimates exceeding 10(8) per ml. Over many years, a consensus has emerged that virus abundances are typically tenfold higher than microbial cell abundances. However, the true explanatory power of a linear relationship and its robustness across diverse ocean environments is unclear. Here, we compile 5,671 microbial cell and virus abundance estimates from 25 distinct marine surveys and find substantial variation in the virus-to-microbial cell ratio, in which a 10:1 model has either limited or no explanatory power. Instead, virus abundances are better described as nonlinear, power-law functions of microbial cell abundances. The fitted scaling exponents are typically less than 1, implying that the virus-to-microbial cell ratio decreases with microbial cell density, rather than remaining fixed. The observed scaling also implies that viral effect sizes derived from 'representative' abundances require substantial refinement to be extrapolated to regional or global scales.
Highlights
Marine viruses are critical drivers of ocean biogeochemistry and their abundances vary spatiotemporally in the global oceans, with upper estimates exceeding 108 per ml
For the near-surface ocean, 44% of the virus-to-prokaryote ratio (VPR) values are between 5 and 15, 16% are less than 5 and 40% exceed 15. This wide distribution, both near- and sub-surface demonstrates potential limitations in utilizing the 10:1 VPR, or any fixed ratio, as the basis for a predictive model of virus abundance derived from estimates of prokaryote abundance
Viruses are increasingly considered as part of efforts to understand the factors controlling marine microbial mortality, productivity, and biogeochemical cycles [8, 9, 19, 39, 45, 55]
Summary
In the compiled marine survey data (see Figure 1, Table S1 and the Materials and Methods), 95% of prokaryote abundances range from 5.0 × 103 to 4.1 × 106 per ml and 95% of virus abundances range from roughly 3.7×105 to 6.4×107 per ml (Figure 2A). For the near-surface ocean, 44% of the VPR values are between 5 and 15, 16% are less than 5 and 40% exceed 15 This wide distribution, both near- and sub-surface demonstrates potential limitations in utilizing the 10:1 VPR, or any fixed ratio, as the basis for a predictive model of virus abundance derived from estimates of prokaryote abundance
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