Diversity and Community Structure of Eukaryotic Phototrophs in the Bering and Chukchi Seas
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Diversity and community structure of eukaryotic phototrophs in the Bering and Chukchi seas Item Type Thesis Authors Lekanoff, Rachel M. Download date 05/10/2021 15:16:14 Link to Item http://hdl.handle.net/11122/11279 DIVERSITY AND COMMUNITY STRUCTURE OF EUKARYOTIC PHOTOTROPHS IN THE BERING AND CHUKCHI SEAS By Rachel M. Lekanoff, B.S., B.A. A Thesis in Partial Fulfillment of Requirements for the Degree of Master of Science in Oceanography University of Alaska Fairbanks May 2020 APPROVED: R. Eric Collins, Committee Co-Chair Andrew M.P. McDonnell, Committee Co-Chair Seth L. Danielson, Committee Member Russell R. Hopcroft, Chair Department of Oceanography S. Bradley Moran, Dean College of Fisheries and Ocean Sciences Michael Castellini, Dean of the Graduate School ABSTRACT The phytoplankton of the Bering and Chukchi seas support highly productive ecosystems characterized by tight benthic-pelagic coupling. In this study, we focus on the northern Bering and Chukchi seas, considering them as one ecosystem. This community has historically been dominated by diatoms; however, climate change and accompanying warming ocean temperatures may alter primary producer communities. Using metabarcoding, we present the first synoptic, high-throughput molecular phylogenetic investigation of phytoplankton diversity in the Bering and Chukchi seas based on hundreds of samples collected from June to September in 2017. We identify the major and minor taxonomic groups of diatoms and picophytoplankton, relative abundances of genera, exact sequence variants (201 for diatoms and 227 for picophytoplankton), and describe their biogeography. These phylogenetic insights and environmental data are used to characterize preferred temperature ranges, offering insight into which specific phytoplankton (Chaetoceros, Pseudo-nitzschia, Micromonas, Phaeocystis) may be most affected as the region warms. Finally, we investigated the likelihood of using shipboard CTD data alone as predictive variables for which members of phytoplankton communities may be present. We found that the suite of environmental data collected from a shipboard CTD is a poor predictor of community composition, explaining only 12.6% of variability within diatom genera and 14.2% variability within picophytoplankton genera. Clustering these communities by similarity of samples did improve predictability (43.6% for diatoms and 32.5% for picophytoplankton). However, our analyses succeeded in identifying temperature as a key driver for certain taxa found commonly throughout the region, offering a key insight into which common phytoplankton community members may be affected first as the Alaskan Arctic continues to warm. i TABLE OF CONTENTS ABSTRACT..................................................................................................................................... i TABLE OF CONTENTS................................................................................................................ ii LIST OF FIGURES ...................................................................................................................... iv LIST OF TABLES ........................................................................................................................ vi ACKNOWLEDGMENTS ............................................................................................................ vii INTRODUCTION .......................................................................................................................... 1 MATERIALS AND METHODS.................................................................................................... 5 Sampling Sites............................................................................................................................. 5 Nutrients and Chlorophyll........................................................................................................... 7 Microbe and Particle Filtration ................................................................................................... 7 CHN and SPM Analyses ............................................................................................................. 7 DNA Sequencing......................................................................................................................... 8 Data Analysis .............................................................................................................................. 9 RESULTS ..................................................................................................................................... 11 Environmental Conditions......................................................................................................... 11 Taxonomic Diversity................................................................................................................. 14 Overall Structure.................................................................................................................... 14 Size Structure......................................................................................................................... 15 Diversity within Genera......................................................................................................... 15 Diatoms.................................................................................................................................. 17 Picophytoplankton ................................................................................................................. 19 Community Clustering .............................................................................................................. 21 Diatom Assemblages ............................................................................................................. 21 ii Diatom assemblage spatiotemporal distributions ............................................................. 24 June ............................................................................................................................... 24 August ........................................................................................................................... 24 August-September......................................................................................................... 24 Picophytoplankton Assemblages ........................................................................................... 27 Picophytoplankton assemblage spatiotemporal distributions ........................................... 30 June ............................................................................................................................... 30 August ........................................................................................................................... 30 August-September......................................................................................................... 30 Environmental Drivers of Community Variability ................................................................... 32 Aggregation by Taxonomy .................................................................................................... 32 Aggregation by Cluster.......................................................................................................... 33 Temperature Effects on Community Structure...................................................................... 35 DISCUSSION ............................................................................................................................... 41 Drivers of Community Structure............................................................................................... 41 Diversity, Community Resilience, and Potential Impacts of a Warmer Arctic ........................ 42 Top-Down and Bottom-Up Controls on Community Structure................................................ 45 Taxonomic Resolution and Environmental Influence............................................................... 47 CONCLUSIONS AND FUTURE WORK ................................................................................... 49 REFERENCES ............................................................................................................................. 51 iii iv LIST OF FIGURES Figure 1: Map of sampling sites...................................................................................................... 6 Figure 2: Sea surface temperature (°C) at each sampling site for each cruise in the northern Bering and Chukchi seas during the spring and summer of 2017. ................................................12 Figure 3: Temperature-Salinity plots of water sampled in the northern Bering and Chukchi seas during the 2017 cruises overlaid with environmental metadata:................................................... 13 Figure 4: The proportion of each exact sequence variant within each phytoplankton size fraction for the northern Bering and Chukchi seas during 2017....................................................16 Figure 5: Cumulative percentile of diatom ESVs across the northern Bering and Chukchi seas cruises during 2017. ......................................................................................................................17 Figure 6: Cumulative percentile of picophytoplankton ESVs across the northern Bering and Chukchi seas cruises during 2017.................................................................................................19 Figure 7: Hierarchical clustering of samples based