**Preface to "Marine Fungus"**

Microbes are the central players in the ecology and biogeochemistry of marine systems. Yet, most of the research on microbial ecology in oceans has been performed on prokaryotes and eukaryotic phytoplankton, and fungi have been essentially neglected in open-ocean studies. One of the main reasons why the ecology of fungi in pelagic oceanic environments has been overlooked thus far is probably the preconception that fungi are outcompeted by prokaryotes when living in a resource-limited liquid environment such as the ocean. Most of the available studies on marine fungi are based on the isolation and identification of fungi from different surfaces (e.g., submerged wood, sediments, macrophytes), mostly in coastal benthic environments. However, recent evidence suggests that fungi are also present in the oceanic water column, mainly associated to particles, with the genomic potential to significantly contribute to marine biogeochemical cycles. Still, we lack even basic information on the ecology of the oceanic mycobiome, precluding us from determining the ecological role of this enigmatic kingdom in our oceans. The aim of this book and Special Issue is to focus on the ecology of marine fungi. Topics include, fungal abundance, distribution, activity, and phylogenetic and/or functional diversity in coastal to open ocean environments, including seawater column and sediments, derived both from laboratory and field studies.

> **Federico Baltar** *Editor*
