UC San Diego

In this dissertation I examined the dynamic seasonal and interannual patterns of phytoplankton communities in the coastal waters of the Western Antarctic Peninsula (WAP). The rapid warming of the WAP has led to significant changes in environmental conditions, yet the impact on phytoplankton communities, particularly in relation to environmental drivers, remains poorly understood. In examining a synthesis of 245 published studies, including 42 key works, I recognized discrepancies in the conclusions regarding observed coastal phytoplankton succession responses to environmental conditions such as changing temperature and salinity that may likely arisen from overly sparse sampling. This highlights the need for coordinated high-frequency sampling to improve understanding of phytoplankton dynamics in response to climate change. I demonstrated the transformative role polar tourism could play in expanding our knowledge (Cusick et al. 2020), showing how data collected aboard expedition vessels can significantly enhance the spatial and temporal resolution of ecological studies in remote regions, while also addressing the critical need for community engagement in advancing polar research. My data were acquired through four 5-month sampling seasons along the WAP (61°S–68°S) through a participatory “citizen” science program, “FjordPhyto”. Using metabarcoding sequencing of samples, I identified 65 phytoplankton taxa across seven major groups revealing high interannual variability in phytoplankton community structure. I investigated how environmental variables, particularly sea surface temperature and salinity, shape phytoplankton succession and community structure. Diatoms dominated early-season cold, salty waters, while mixotrophic species such as dinoflagellates, marine stramenopiles (MAST), and haptophytes increased in richness later in the season with warm and fresh conditions. Diatom species showed high interannual variability with significant correlation to timing, temperature, and salinity, and each season featured a consistent low-salinity assemblage of 4-6 diatom species and 1-2 dinoflagellate species, though the exact combination changed each year. A revised conceptual mandala based on these data shows two possible succession sequences: a main sequence in early season with diatoms or an alternate sequence with cryptophytes and dinoflagellates. This mandala offers insights into community responses to environmental drivers. By integrating traditional and innovative methodologies within a participatory science framework, my dissertation advances understanding of protist biodiversity in the WAP.