Marine fungal dark matter in the global ocean

Marine fungi are a major part of ‘microbial dark matter’, with most organisms known from sequence data and currently not in culture. Interest in marine fungi has substantially increased over the past decade, and studies using culture independent methods have indicated that fungal diversity in the oceans may be greater than previously estimates based on cultivation alone. There remains much to learn about the true diversity of marine fungi in the global oceans and the ecological roles that they could play. The Tara Oceans expedition has allowed for significant advancements in our understanding of the global diversity of planktonic microorganisms. Interrogation of the Tara Oceans 18S rRNA gene dataset for fungal sequences shows that fungi are found throughout the global oceans, appearing in all marine regions covered by the Tara Oceans expedition. In the survey, Ascomycota and Basidiomycota were common, while some locations had increased abundances of Chytridiomycota. Differences in community composition were observed between oceanic regions and, although clear signals were not apparent due to the nature of the sampling, there was some indication of community variation between upwelling, coastal, shelf and gyral provinces. Different size sampling fractions appeared to capture different portions of the pelagic fungal community. These findings highlight a number of ecological questions: How important are oceanic currents in determining fungal biogeography? What is the relationship between marine fungi and biogeochemical processes? What is actually there? By targeting these questions directly, we will be able to bring the dark matter of marine fungi into the light.