Interactions between the filter-feeding appendicularian Oikopleura dioica and the abundance and fate of marine viruses

Kyle Mayers1, Janice Lawrence2, Joachim Töpper3, Katrine Sandnes Skaar1, Elzbieta Petelenz4, Aud Larsen1, Gunnar Bratbak4 and Jessica Louise Ray5, (1)NORCE Norwegian Research Centre, Bergen, Norway, (2)University of New Brunswick, NB, Canada, (3)Norwegian Institute for Nature Research, Norway, (4)University of Bergen, Norway, (5)NORCE Norwegian Research Center, Bergen, Norway
Marine viruses are the most abundant entity in the oceans, regulating microbial populations and biogeochemical cycles through infection and lysis of cells. Factors that regulate their abundance will therefore alter these processes. Our group has previously demonstrated that the globally distributed appendicularian Oikopleura dioica is able to remove the Emiliania huxleyi virus from seawater, with viral DNA observed in houses, guts and faecal pellets of O. dioica. However, the ability of this zooplankton to feed on other marine viruses has yet to be explored.

We therefore tested how well O. doica was able to clear seawater for viruses ranging in size from ~120-310 nm. We incubated viruses of 3 phytoplankton and 2 marine bacteria species in the presence and absence of O. doica and sampled hourly for quantification of viral abundance for 8 hours and again at 24 hours. The viruses differ in morphology and infection strategy, and include those of bloom forming algae (Micromonas pusilla), globally distributed haptophytes (Prymnesium kappa, Haptolina ericina) and marine bacteria (sulfitobacter, Synechococcus sp.). Faecal pellets from experiments were collected and incubated with fresh algae cultures to determine if pellets can act as a reservoir for infectious virus particles.

Here we show that O. dioica was able to clear most viruses tested to varying degrees. Rates of clearance ranged from ~8 to 68 mL animal-1 d-1, with the larger viruses demonstrating higher clearance rates, suggesting a potential size selection mechanism. We observed that all viruses retain some level of infectivity even after gut passage.

These results suggest that appendicularians can filter a wide variety of marine viruses, and play significant roles in virus loss or dispersal through faeces. We display a novel food-web interaction from marine viruses to appendicularians. Alterations in virus-host dynamics, here regulated by O. dioica, will influence the viral mediated turnover of carbon and nutrients within pelagic environments.