VIROVAC: Filter-feeding mesozooplankton as uncharted accomplices in marine virus ecology

Viruses fill the world's oceans, more so than any other biological units on
the planet! Even though viruses are not "alive", they are critical regulators
of the diversity of organisms and the efficiency of biochemical processes
that occur in the oceans. Despite this, we know very little about viruses, and in particular about how these tiny entities persist and spread. One group of marine animals, the planktonic tunicates known as appendicularians, are specialists when it comes to feeding on low amounts of small food particles. In fact, the filtering "houses" that they live inside and use to trap food particles are so efficient that they can even trap large viruses. This suggests that viruses can not only prey upon host organisms, but that they themselves can end up on the menu for small-particle specialists like appendicularians. Although being trapped in the filtering house of an appendicularian may mean digestion for a virus particle, the rapidity with which appendicularians change their houses and empty their guts gives any trapped viruses a likelihood of survival, either trapped in a discarded house or inside a faecal pellet, both of which sink rapidly to the ocean floor. The interaction between appendicularians and viruses thus stands to reshape our understanding not only of the role of viruses in the ocean, but also of the mechanisms for how viruses may persist and spread both in space and in time. Which viruses can be trapped and ingested by appendicularians? How many viruses sink to the ocean floor trapped inside appendicularian houses and faecal pellets? How does trapping inside houses and faecal pellets affect the persistence of virus infectivity relative to free-floating viruses over time? In the VIROVAC project, researchers at Uni Research Environment and the University of Bergen will attempt to answer these questions using a combination of laboratory experiments and field sampling. They are assisted by colleagues in Canada and Israel.