Recent molecular evidence suggests a global distribution of marine fungi; however, the ecological relevance and corresponding biological contributions of fungi to marine ecosystems remains largely unknown. We assessed fungal biomass from the open Arctic Ocean by applying novel biomass conversion factors from cultured isolates to environmental sterol and CARD-FISH data. We found an average of 16.54 nmol m−3 of ergosterol in sea ice and seawater, which corresponds to 1.74 mg C m−3 (444.56 mg C m−2 in seawater). Using Chytridiomycota-specific probes, we observed free-living and particulate-attached cells that averaged 34.07 µg C m−3 in sea ice and seawater (11.66 mg C m−2 in seawater). Summed CARD-FISH and ergosterol values approximate 1.77 mg C m−3 in sea ice and seawater (456.23 mg C m−2 in seawater), which is similar to biomass estimates of other marine taxa generally considered integral to marine food webs and ecosystem processes. Using the GeoChip microarray, we detected evidence for fungal viruses within the Partitiviridae in sediment, as well as fungal genes involved in the degradation of biomass and the assimilation of nitrate. To bridge our observations of fungi on particulate and the detection of degradative genes, we germinated fungal conidia in zooplankton fecal pellets and germinated fungal conidia after 8 months incubation in sterile seawater. Ultimately, these data suggest that fungi could be as important in oceanic ecosystems as they are in freshwater environments.

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We would like to acknowledge the funding support provided by UiT - the Arctic university of Norway and the Tromsø Research Foundation under the project Arctic SIZE, number 01VM/H15. We greatly acknowledge the support by the science team and the crew of the RV Polarstern and the grant support from AWI_PS106_00. We would like to thank Paul Dubourg and Roy Andres Lysa from the University of Tromsø for assistance with the CHN analyzer and with the flow cytometer, respectively, as well as Randi Olsen and Augusta Hlin Aspar Sundbø for assistance with laser scanning microscopy. We would like to acknowledge Céline Heuzé for generating CTD profiles and Thomas Isakeit from Texas A&M University for his spore trap. Analytical chemistry was supported by a United States Department of Agriculture's Agriculture and Food Research Initiative grant (2017-67013-26524). Sequencing data has been submitted to the NCBI SRA under BioBroject ID PRJNA449189, accession SAMN08888854–SAMN08888884. Microarray data have been archived in NCBI GEO, under accession GSE117831, GSM3309953–GSM3309954.

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  1. UiT Norges arktiske universitet, BFE, NFH bygget, Framstredet 6, 9019, Tromsø, Norway

    • B. T Hassett
    • , T. R. Vonnahme
    • , T. Rämä
    •  & R. Gradinger
  2. Texas A&M University, 435 Nagle Street, 2132 TAMU, College Station, TX, 77833, USA

    • E. J. Borrego
    •  & M. V. Kolomiets


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