Chytrid fungi distribution and co-occurrence with diatoms correlate with sea ice melt in the Arctic Ocean

Estelle S Kilias,Katja Metfies,Guy Leonard,Thomas A Richards,Luka Šupraha,Leandro Junges

doi:10.1038/s42003-020-0891-7

Abstract

Global warming is rapidly altering physicochemical attributes of Arctic waters. These changes are predicted to alter microbial networks, potentially perturbing wider community functions including parasite infections and saprotrophic recycling of biogeochemical compounds. Specifically, the interaction between autotrophic phytoplankton and heterotrophic fungi e.g. chytrids (fungi with swimming tails) requires further analysis. Here, we investigate the diversity and distribution patterns of fungi in relation to abiotic variables during one record sea ice minimum in 2012 and explore co-occurrence of chytrids with diatoms, key primary producers in these changing environments. We show that chytrid fungi are primarily encountered at sites influenced by sea ice melt. Furthermore, chytrid representation positively correlates with sea ice-associated diatoms such as Fragilariopsis or Nitzschia. Our findings identify a potential future scenario where chytrid representation within these communities increases as a consequence of ice retreat, further altering community structure through perturbation of parasitic or saprotrophic interaction networks.

Highlights

Global warming is rapidly altering physicochemical attributes of Arctic waters
The discovery of this diversity has led to the hypothesis that bona-fide marine fungi operate as a trophic ‘bridge’ for carbon and nitrogen substrate transfer between recalcitrant phytoplankton such as diatoms and wider nodes on the marine food-web, e.g., zooplankton[8,9]
In summer 2012, the Arctic Ocean experienced an unprecedented decline in sea ice, resulting in a record sea ice minimum[5]

Summary

Introduction

Global warming is rapidly altering physicochemical attributes of Arctic waters. These changes are predicted to alter microbial networks, potentially perturbing wider community functions including parasite infections and saprotrophic recycling of biogeochemical compounds. Climate-driven changes to local physicochemical properties are profound in the Arctic Ocean, for example, leading to increases in temperature, light availability and decreases in sea ice concentration and surface water salinity These changes have been shown to alter microbial community structure[4,5,6]. Marine-derived fungi have received an increase in attention after high-throughput diversity tag-sequencing has revealed an uncharacterised diversity of fungi and fungal-like ribosomal RNA (rDNA) phylotypes in marine environments[7] The discovery of this diversity has led to the hypothesis that bona-fide marine fungi (fungi recovered from sea water, which represent a functional player in the marine ecosystem, rather than a spore in transit) operate as a trophic ‘bridge’ for carbon and nitrogen substrate transfer between recalcitrant phytoplankton such as diatoms and wider nodes on the marine food-web, e.g., zooplankton[8,9]. Other zoosporic fungi include members of the group Blastocladiomycota or Cryptomycota/Rozellomycota but these groups are not a major focus of this study

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