Rebecca Crawford

Topic

Spatial and Seasonal Variability in Eukaryotic Phytoplankton Composition in the Arctic Ocean Revealed with Metabarcoding Analysis

Department of Biology

Date & location

• Friday, April 5, 2024
• 9:00 A.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. Ryan Gawryluk, Department of Biology, University of Victoria (Co-Supervisor)
• Dr. Diana Varela, Department of Biology, UVic (Co-Supervisor)
• Dr. John Nelson, Department of Biology, UVic (Member)

External Examiner

• Dr. Erin Bertrand, Department of Biology, Dalhousie University

Chair of Oral Examination

• Dr. John Volpe, School of Environmental Studies, UVic

Abstract

Rapid environmental shifts in Arctic Oceans have brought increased attention to their biodiversity. Environmental changes in the Bering and Chukchi Seas are especially concerning, as these regions are among the most productive in the world’s oceans, and their fisheries contribute to both local and global food systems. Predicting the impacts of climate change requires understanding biodiversity at the base of the food web, including eukaryotic phytoplankton, and the environmental drivers affecting them. This study evaluated the variability in the structure of phytoplankton communities at spatial and inter-annual scales in the Pacific Arctic Region (2021 and 2022) and at a seasonal scale in the Canadian Arctic (September 2019 to July 2020) using metabarcoding of the V4 18S rRNA gene. The community structure of eukaryotic phytoplankton exhibited both strong spatial and temporal trends, and was influenced by temperature and nutrient concentrations, as well as by sea ice extent and thickness in the Pacific Arctic Region. The chain-forming diatoms Chaetoceros and Thalassiosira were responsible for the high phytoplankton biomass of this region and were associated with colder temperatures and higher nitrate concentrations, aligning with previous observations. The community composition also varied from year to year, with the picoprasinophyte, Micromonas, and the prymnesiophyte, Phaeocystis, contributing to a larger proportion of the overall phytoplankton community, particularly in surface waters, in 2022 compared with 2021. In addition, several potentially toxigenic algae, including Alexandrium, Aureoccocus and Pseudo-nitzschia were present in the Pacific Arctic and were generally associated with warmer temperatures. In the Canadian Arctic, we observed distinct seasonal changes in phytoplankton community structure including a polar winter community dominated by dinoflagellates, a spring under ice community dominated by Phaeocystis, and a late spring/summer community composed largely of Micromonas with an increase in Chaetoceros by July with the onset of sea ice melt. These findings add to our understanding of phytoplankton community composition in the Pacific and Canadian Arctic and help to resolve the spatial and temporal knowledge gaps within these sensitive regions.