Seabirds are integral predators in marine ecosystems and ideal indicators of ocean health and productivity. Along the west coast of North America, the dynamic California Current Ecosystem (CCE) provides vital foraging habitat to a variety of resident and migratory marine birds. The CCE is a complex current system that is highly variable over different spatial and temporal scales. Within the CCE, there is a web of different marine protected areas, including five National Marine Sanctuaries (NMS). These NMSs are found in the southern, central and northern portion of the CCE and provide well-defined regions to compare patterns and changes in seabird distributions throughout the CCE. Although seabirds within the CCE are well studied, it is only recently that the majority of at-sea data on seabirds in the CCE have been consolidated into one dataset that spans from 1980 to 2017. In addition, there are broad spatial patterns and temporal trends that remain unresolved about seabirds within the CCE. Understanding such trends will provide valuable information on how seabird density, diversity, and community composition may change in association with natural environmental variability and long-term impacts from climate change. Here, I use the most extensive data available on seabirds at-sea in the CCE to: (1) describe broad spatial patterns of seabird indices of density, diversity and community composition, (2) determine fine scale temporal trends of these seabird indices within NMSs, and (3) use diverse sources of data, including citizen science, to investigate relationships between vagrant, tropical birds and environmental variables. I found higher seabird abundance and diversity within higher latitudes and nearshore habitats, and that west coast NMS capture important seabird habitat, with greater abundance and diversity than outside the sanctuary boundaries. However, I found that the abundance of avifauna within the NMS in the CCE has decreased since the 1980’s, with greater declines in south. Decreases were largely due to a decline in non-CCE breeding species, which had decreased in abundance within all five NMS. Relationships between the abundance of seabirds with environmental conditions varied among the NMS, indicating that there are distinct drivers within each of these regions. Through investigation into five tropical species, I found that all of these species had increased in the CCE and their rise in abundance was linked with the two intense marine heatwaves that occurred in the 2010’s. With these increases, there were some species that persisted at high abundances, and others that did not remain at high numbers after these warm water events. This research results in a detailed description of the spatial patterns of seabirds in the CCE, trends of seabirds within NMS, and documented the northward range expansion of five tropical species.

The Western Antarctic Peninsula (WAP) is rapidly changing due to climate forcing in recent decades. These changes manifest as an overall increase in ocean and air temperatures (with some regional cooling), retreating glaciers, and increases in precipitation associated with shifts in atmospheric circulation. As these changes continue and intensify, meteoric water input to the coastal ocean is expected to increase. Continued monitoring of these changes can help us better understand their impacts. The physical effects of glacial melting on sea level has been extensively studied in the past. However, the impact of glacial meltwater on phytoplankton community composition remains largely elusive. Due to the critical role of primary producers in the Antarctic food web and their significance to local biogeochemical cycle and ecosystem dynamics, the immediate ramification of meltwater input on these communities need to be better understood.

In order to accomplish such task, robust datasets are required that can encompass both long-term temporal scale and broad geographic extent. Coincidentally, these datasets exist in the Western Antarctic Peninsula region. Two oceanographic expeditions (FjordEco) were conducted in an Antarctic fjord (Andvord Bay) in November to December 2015 and April to May 2016. This dataset provides insights on nearshore water properties and how they impact phytoplankton community. Over the Peninsula shelf, a multi-decadal time series was curated and collected by the Palmer Long-Term Ecological Research (LTER) program. The LTER database has extensive spatial and temporal coverage which make it suitable for understanding the impact of environmental variables on phytoplankton over the continental shelf.

This dissertation contains three main chapters. In Chapter 2, I aim to understand the spatial and temporal distribution of glacial meltwater in Andvord Bay and characterize their optical features in order to develop a method for quantifying meltwater fraction based on water column optics. The fjord severs as an end-member and thus an extreme in various environmental and biological gradients. Hence, the ecological connectivity between the fjord and the shelf has significant implications to the entire Antarctic ecosystem. In Chapter 3, I will investigate the phytoplankton community composition within Andvord Bay and understand how environmental conditions, particularly meltwater, impact this community. The data from this chapter will be utilized to train a machine learning model; techniques developed in this chapter will be applied to the broader coastal ocean over the WAP continental shelf in Chapter 4. I hope this dissertation can improve our understanding of how environmental variables influence phytoplankton community in the WAP, as well as contextualize the physical impacts of climate forcing in the perspective of Antarctic ecosystems.

The western Antarctic Peninsula is rapidly warming and its high-latitude fjord ecosystems are expected to be highly sensitive to climate warming (Weslawski et al. 2011; Cook et al. 2016). As the region continues to change, understanding the current nutrient budget will allow for better predictions of ecosystem response at all levels of the food web to variable future conditions. Analysis from two synoptic transects along Andvord Bay, bracketing the 2015-2016 austral summer, allows for primary production to be assessed through the depletion of dissolved inorganic nutrients, nitrate and silicate. Andvord Bay is a quiescent system that can experience surface nutrient replenishment during katabatic wind events otherwise sustaining favorable growth conditions throughout an extended growth season. The high concentration of surface nitrate and minimal presence of reduced nitrogen species in spring suggests new production dominates the early season while an observed four-fold increase in ammonium would support late season recycled production. Silicate depletion indicates 25-68% of the primary production in Andvord Bay was from diatom growth from December 2015 to April 2016. Modifications were made to the nutrient drawdown method for primary production estimation to adapt to conditions unique to the Andvord Bay region, replacing the baseline winter water requirement and adapting the growth periods. Applied, this method yields reasonable, conservative estimates for net community new production indicating greater production inside the fjord than the outside waters of the Gerlache Strait and supporting the hypotheses that fjords in the WAP are hot-spots of productivity.

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.

The Arctic Ocean contributes 5–14% of global CO₂ uptake via primary production, with diatoms as the dominant phytoplankton. Rapid Arctic warming—occurring at four times the global average—has increased glacial meltwater input into fjords, altering salinity, temperature, and nutrient availability. Given the complex biogeochemistry of fjord systems, it is unknown exactly how changes in the environment impacts the metabolic processes and tenacity of diatoms in nutrient-limited and nutrient-rich conditions.

This study focuses on Sermilik, a fjord on Greenland’s southeast coast connected to several major glaciers. During the 2019 summer season, samples were collected along a 78 km transect. CTD profiles, nutrient concentrations, pigment data, and RNASeq-based metatranscriptomes were used to examine diatom gene expression at the surface and deep chlorophyll maximum (DCM). Data analysis and visualization were conducted in Python and R.

We found that stations closer to the glacial termini had cooler, fresher waters with higher measurements of nitrate and silicic acid. These conditions were correlated with higher gene expression of processes tied to growth and protein production, especially at the DCM where nitrate values always exceeded those at the surface. Despite differences in conditions at the surface and DCM, salinity still remained a large determinant in shaping the metabolic state of the diatoms.

Our findings reveal how glacial melt-driven nutrient input and environmental changes influence diatom gene expression in an Arctic fjord. Understanding these dynamics is crucial for predicting future shifts in Arctic primary productivity under continued climate change.