Sea-ice microbial community succession and the potential role of parasitoids in the maintenance of diversity during the spring bloom

Abstract Sea ice is a crucial, yet declining, habitat in high latitude ecosystems. Here we present a high-temporal resolution amplicon sequence data set collected during the spring ice-algal bloom near Utqiaġvik, Alaska in 2021 to study sea-ice microbial dynamics. The ice-algal bloom peaked on May 8th, reaching 46.6 mg chlorophyll a m-2, and thereafter became limited by nitrate availability. A massive bloom of the oil-degrading bacterium, Oleispira (>80% relative abundance), coincided with the algal bloom raising questions about hydrocarbon exposure. The sea-ice algal bloom was dominated by diatoms, particularly Nitzschia spp., and transitioned into a flagellate dominated post-bloom community which aligned with melt-associated changes to the physicochemical environment. We explored the relationship between putative parasitoids, Chytridiomycetes, Thecofilosea (Cercozoa), Oomycetes, Syndiniales (Dinoflagellata), and Labyrinthulomycetes (Bigyra), and potential microalgal hosts. Chytrids peaked periodically suggesting synchronized infections and Cryothecomonas (Thecofilosea) was observed parasitizing Nitzschia spp. for the first time in Arctic sea ice. Co-occurrence analysis suggested that diatoms, especially Nitzschia, were the primary hosts of Pacific-Arctic parasitoids, and that top-down parasitoid control may dramatically alter community composition over short timescales, such as days. These results provide important insights into the drivers of spring bloom timing and maintenance of microalgal diversity in sea ice. Competing Interest Statement The authors have declared no competing interest. Footnotes Email addresses: lmwhitmore{at}alaska.edu; amaguilarislas{at}alaska.edu; channing.e.bolt2.civ{at}us.navy.mil; kenneth.dumack{at}uni-koblenz.de; mjin{at}alaska.edu; mrkaufman{at}alaska.edu; moggier{at}alaska.edu; gmhennon{at}alaska.edu Conflict of Interest: The authors declare no conflict of interest. Data Availability: Biogeochemical data are available through the Arctic Data Center, doi:10.18739/A21J9793S (Whitmore et al., 2024), and DNA sequencing data are available through NCBI’s SRA under BioProject PRJNA1108783. Taxonomically annotated Raw read counts are available as a supplementary dataset Supplementary Information (Table S1 & S2). Data processing and analysis R scripts are publicly available on GitHub at https://github.com/kbdilliplaine/2021-Utqiagvik-time-series.git. Considerable revisions were made to main body text and the supplementary materials. Formatting of figures and tables also occurred. https://arcticdata.io/catalog/view/doi:10.18739/A21J9793S https://github.com/kbdilliplaine/2021-Utqiagvik-time-series.git