EXPANDING OUR UNDERSTANDING OF MARINE MICROBIOTA IN THE NORTHWEST ATLANTIC AND ARCTIC SECTORS: FROM COASTAL PHYTOPLANKTON TO DIAZOTROPH COMMUNITIES

Abstract

High-resolution ocean time series and strategic sampling in understudied environments provide unique opportunities to advance our knowledge of microbial life in the ocean. The goal of this thesis was to expand our understanding of the marine microbiome by focusing on phytoplankton and diazotrophs within the Northwest Atlantic (NWA) and Arctic Ocean sectors through the use of environmental DNA collected from: (i) a weekly multiyear time series located in Bedford Basin (N.S., Canada; samples from 2014–2019), and (ii) the understudied Canadian Arctic Gateway (CAG) during Jul–Aug 2015. This thesis has three main research chapters. In Chapter 2, I describe the dominant phytoplankton present in the coastal NWA over four years, providing the first detailed molecular picture of phytoplankton biodiversity across all seasons within this region of the Atlantic Ocean. In Chapter 3, I focus on the globally important diazotroph symbiont, Candidatus Atelocyanobacterium thalassa or ‘UCYN-A’ within the Bedford Basin over three years by describing the weekly dynamics of four ecotypes within this species (A1 to A4). Ultimately, findings from Chapter 3 advance our understanding of UCYN-A temporal dynamics within the coastal realm and further elucidate microevolutionary patterns demonstrated by ecotypes of this species. In Chapter 4, I move outside of the Bedford Basin and characterize UCYN-A and other diazotrophs within the CAG during the late summer and early fall of 2015. Importantly, findings from Chapter 4 provide an initial account of the possible biogeographic distributions that marine diazotrophs in the CAG can exhibit across the Labrador Sea, Baffin Bay, and Canadian Arctic Archipelago. Chapter 4 also increases the overall survey of marine diazotrophs within the Arctic (for which previous data are sparce) by elucidating the taxonomy and environmental conditions that were associated with diazotroph genetic signatures dominating the CAG diazotroph communities during 2015. Overall, Chapters 2 and 3 advance our understanding of phytoplankton and UCYN-A within the coastal NWA, while Chapter 4 advances our understanding of diazotroph diversity within the Arctic marine environment.