Text

theses

The coccolithophore Emiliania huxleyi is a globally distributed marine algal species that regularly forms large surface ocean blooms that can last from weeks to months. As a cosmopolitan species that also forms calcium carbonate plates called coccoliths, E. huxleyi plays a critical role in influencing both organic and inorganic carbon cycles. North Atlantic blooms of the algae are regularly infected by a double stranded DNA virus called Coccolithovirus (EhV). The ecological and biogeochemical influences of viral infection in marine algae are largely unknown, although studies largely suggest infection enhances chemical cycling within the microbial loop. This dissertation investigates E. huxleyi-EhV interactions within marine algal communities to further elucidate the role viruses play in influencing their host as well as the surrounding ecosystem. On a local scale, this was investigated by locating and interrogating mesoscale North Atlantic blooms of E. huxleyi with a comprehensive toolset using MODIS/AQUA satellite imagery, a suite of diagnostic lipid- and gene-based molecular biomarkers, in situ optical sensors, and sediment traps to show that EhV infections are coupled with particle aggregation, high zooplankton grazing, and enhanced downward vertical fluxes of both particulate organic and particulate inorganic carbon from the upper mixed layer to the mesopelagic. The finding that viruses can stimulate vertical carbon flux through a mechanistic interplay with zooplankton grazers introduces novel complexities into microbial ecosystem interactions. These bloom communities are further investigated using optical absorption spectra, phytoplankton pigment composition, and flow cytometry, revealing EhV infection has little influence driving the variability in phytoplankton absorption compared to community photoacclimation within the blooms. It is further observed that photoacclimation driven absorption characteristics are discernible through different phytoplankton taxonomic compositions. On the global scale, the known biogeography of EhV infection and diversity of EhVs is expanded out of the North Atlantic Ocean using a combination of the Tara Oceans global metagenome database as well as targeted regional sampling throughout the Pacific Ocean. These results reveal that EhV infection is a global phenomenon tightly coupled to E. huxleyi production and is pervasive in bloom and non-bloom environments. Collectively, these studies show that EhVs are an influential regulator of carbon cycling by enhancing biological pump efficiency and through revealing their global distribution in the ocean.

ETD_8733

Ph.D.

Includes bibliographical references

by Christien Philip Laber

doi:10.7282/T3154MHT

ETD doctoral

The author owns the copyright to this work.