Marine microeukaryotes battle every day with environmental pressures, predators and viruses to survive. To escape and survive certain threats they often have to change their life cycle stage for the cost of a lower growth rate. Marine viruses are ubiquitous in the oceans but they are unable to replicate without infecting host cells. Therefore they have to evolve as quickly as their host and change their infection strategy. Spontaneous resistance of the green microalgae Ostreococcus tauri occurs in culture once it is infected with the virus OtV5. Two newly isolated viruses were able to lyse these OtV5-resistant O. tauri cells. While o could only lyse OtV5-resistant cells, OtV15 was able to lyse both OtV5-susceptible and –resistant cells. Similar as the O. lucimarinus viruses, their genomes have a high level of synteny with 182 orthologous genes, reduced to 173 when including OtV1 and OtV2. We will discuss potential infection strategies based upon their specific genes. High-throughput sequencing projects like the Ocean Sampling Day and Tara Oceans Expedition enable us to monitor O. tauri and its viruses around the world.