Effect of concentrating the virus‐rich 2‐2nm size fraction of seawater on the formation of algal flocs (marine snow)

Abstract

Particle aggregates >0.5 mm in diameter (marine snow) are an important component of marine environments. Viruses are now recognized as active members of the marine microbial food web, infecting both planktonic primary producers and bacteria. The effect of adding material from the 2–200‐nm size fraction, concentrated from seawater with ultrafiltration, on the development of phytoplankton biomass and formation of algal flocs was examined. At higher concentrations of material in this size fraction (2.3 times enrichment with virus‐like particles), the buildup of phytoplankton biomass was initially delayed. After 8 d, these enrichments resulted in the formation and persistence of up to 5 times higher numbers of larger aggregates (≥ 1‐mm equivalent spherical diameter) concomitant with even higher phytoplankton biomass. Both the size distribution of algal aggregates and primary production can be affected by material in the size range of 2–200 nm containing large numbers of viruses.