Viruses are by far the most abundant biological entities on the planet. The estimated overall abundance in the world’s oceans is ca. 4 × 1030 (Suttle 2005), a value that exceeds bacterial abundance by one order of magnitude (Whitman et al. 1998; Suttle 2005). Every second, approximately 1023 viral infections occur in the ocean, being a major source of mortality of a wide range of organisms from prokaryotes to whales (Suttle 2005). As a result, viruses play critical roles in shaping aquatic communities and determining ecosystem dynamics (Fuhrman 1999; Suttle 2005).