Arctic Marine Fungi: New Approaches To Discern Ecosystem Relevance

Brandon Hassett, University of Tromsø, Tromsø, Norway
The relevance of fungi to ecosystem processes remains a gap in Arctic marine science. A combination of 18S rRNA high-throughput sequencing and 28S rRNA clone data were used to assess the diversity and community composition of Arctic marine fungi. These data revealed that flagellated fungi within the Chytridiomycota predominate fungal communities in sea ice ecosystems in areas of reduced snow cover with elevated photon flux densities. These sea ice Chytridiomycota phylogenetically branch sister to the Lobulomycetales and represent a previously undescribed clade of life. To assess fungal biomass, ergosterol:carbon ratios were established from marine fungal isolates and paired with novel CARD-FISH probes designed to target Chytridiomycota. Ergosterol was then quantified and Chytridiomycota enumerated from environmental samples from three depths per site. 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 maintaining ecosystem structure. To understand the functional potential of Arctic marine fungi, the GeoChip microarray was used to screen for the presence of genes with known biogeochemical cycling relevance. The microarray detected a suite of functional genes, including the fungal-encoded pectin lyase, which produced the second strongest probe signal from any organism in under-ice sediment. Ultimately, these data suggest that fungi might have a far greater role in Arctic marine ecosystem processes than previously realized.