Abstract
Bacteriophages — also known as phages - are viruses which exclusively infect bacterial cells. They are the most abundant biological entity on the planet and have an essential role in marine ecosystems and controlling biogeochemical cycles. Understanding how viruses are involved is dependent on characterizing viral distribution and the factors controlling them. In this thesis five years’ worth of Illumina short read sequencing data from the Munida Observatory Time Series (MOTS) was used to establish a custom-built pipeline (VOTS) for the processing of short read sequencing data. VOTS aimed to identify the drivers of viral community structure over space and time in MOTS. Key findings were: 1) Temperature, nutrients (NO3-, PO43- and SiO) and distance from land were involved in driving viral community structure; 2) Viral community structure differed over space and time, where deep water phage differed from the surface waters mimicking that of prokaryotes. Deep water phage also had a lower phage abundance, was made up of a higher proportion of novel phage and differed the least seasonally from surface waters. Surface water phage samples did not significantly differ from each other. The viral community composition showed strong seasonality, with the highest diversity and abundance found in Autumn; 3) Most phage identified were novel and unclassified, differed seasonally in abundance, with the most classified as myovirus-like infecting the most dominant host taxa (Proteobacteria and Cyanobacteria). The dominant taxa and their hosts were hypothesized to have a significant role in controlling the energy and nutrient cycles in MOTS. The short read sequencing data analyzed by VOTS provides insights into the drivers of viral community dynamics in marine ecosystems.