Metagenomes are classified from left to right based on the sampling depth as ‘Above the OMZ’, ‘OMZ’, and ‘Below the OMZ’, and vertically ordered based on the geographical sampling region, from the samples closest to Saanich Inlet (on top) to the one farthest from Saanich Inlet (at the bottom). Viral metagenomes are noted with a gray capsid symbol. Each metagenome—viral genome association was classified based on the number of viral genes detected and the amino-acid percentage identity of the BLAST hits associated. The viral genome was thought to be in the sample when more than 75% of the genes were detected at more than 80% of identity in the metagenome (blue cells), when the same ratio of genes detected at lower percentage (60–80%) indicates the presence of a related but distinct virus (green cells). We considered that less than 75% of the genes detected meant that this virus was likely absent from the sample (red cells), except for the detection of the ssDNA Microviridae in HiSeq-Illumina-sequenced viromes, where the procedure used to process samples prior to sequencing is likely to select against the amplification of ssDNA templates (gray cells). Metagenomes in which the associated SUP05 host was detected are highlighted in black (>75% genes on SAG microbial contigs covered with Average Nucleotide Identity > 95%).