Figure 5. Empirical basis for the size-fractionation approach and the choice of sampling devices.

The horizontal plane shows the range of body/cell size and natural abundances reported in the literature (Table 2) for viruses (including giant viruses), prokaryotes, protists and metazoans (coloured boxes). The sampling devices used to collect plankton <5 μm in size (i.e., high volume peristaltic pump and rosette with Niskin bottles) and >5 μm in size (i.e., plankton nets) are illustrated as well on the horizontal plane. The vertical plane shows the volume of seawater required to capture 100, 75 and 50% of species richness reported in the literature (Table 2) for viruses (including giant viruses), prokaryotes, protists and metazoans (shaded boxes). The typical volume of seawater collected by sampling devices are shown in comparison (horizontal thick lines). Also illustrated on the vertical plane: Sieves were used to remove large organisms from protists net samples.