| Summary: | Little is known about the molecular diversity of the phytoplankton inhabiting the fjords of the West Antarctic Peninsula (WAP), despite the status of this region as being among the most vulnerable to future warming. Additionally, there are many gaps in our knowledge of how polar phytoplankton will respond to the effects of climate change or about the unique life history strategies they may have evolved. The main objective of this dissertation is to develop an improved understanding of the physiology of a model polar phytoplankton species and to characterize phytoplankton community structure in terms of molecular diversity in a climate-sensitive polar environment. The phytoplankton community in a WAP fjord was surveyed by sequencing the V9 region of the 18S rRNA gene and the V1-V2 region of the plastid derived 16S rRNA gene (Chapter 2). In addition, photosynthetic cells were enumerated by flow cytometry. A novel cryptophyte was observed and the phylogeny and global distribution of this cryptophyte was then examined. Among other phytoplankton, the picoprasinophyte, Micromonas polaris, was also observed in these Antarctic samples. With the genome of M. polaris CCMP2099 newly in hand, we aimed to improve our understanding of how polar phytoplankton may respond to the future effects of climate change by examining M. polaris’ physiological and transcriptional responses to changing CO2 and nitrate conditions in continuous-flow photo-bioreactors (Chapter 3). Finally, we explored the potential survivability and transcriptional responses by this alga as it descends to the deep ocean, building on prior observations of M. polaris in North Atlantic Deep Water, using a series of in situ incubation experiments (Chapter 4). Collectively, these studies provide baseline information on polar phytoplankton community structure and physiological capability, which will help to guide future assessments of the phytoplankton in these regions under a changing climate.
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