Diversity and seasonal dynamics of marine haptophytes and their viruses

Members of the division Haptophyta are phytoplankton and a major component in marine pico- and nanoplankton communities. They often occur in bloom concentrations that may have a major impact on the global carbon balance, on climate forcing and sometimes cause fish-kills. Because haptophytes are small and difficult to identify in the microscope little is known about their seasonal dynamics and ecological role at the species level. We have studied the diversity and seasonal dynamics of marine haptophytes and their viruses, and how species composition and diversity are related to environmental factors using 454 pyrosequencing, complemented with electron microscopy and flow cytometry. This study revealed higher species richness of haptophytes than previously observed in the area with electron and light microscopy. The majority of the OTUs matched genetically uncharacterised taxa, most of which were affiliated with the order Prymnesiales. Several of the OTUs matched sequences forming deep-branching lineages, potentially representing novel classes of haptophytes. Haptophyte richness and community composition exhibited high temporal variation and significant yearly periodicity, with highest richness in autumn and lowest in the spring. Some taxa, such as some bloom forming species were present all year round, whereas most coccolithophores only appeared from summer to early winter. Also the algal virus (Phycodnaviridae) diversity was high and showed seasonal variations. Our results indicated that the abiotic factors only accounted for about 30% of the variation, and suggests that biotic factors may explain some of the residual variation.