Fungal parasites infect marine diatoms in the upwelling ecosystem of the Humboldt Current System off central Chile.

This is the first report of fungal parasiti sm of diatoms in a highly productive coastal upwelling ecosystem, based on a year-round time series of diatom and parasitic Chytridiomycota abundance in the Humboldt Current System off Chile (36830.80’S-73807.70’W). Our res ults show co-variation in th e presence of Skeletonema, Thalassiosira and Chaetoceros diatoms with atta ched and detac hed chytrid sporangia. High abundance of attached sporangia was observed during the austr al spring , coinciding with a predominance of Thalassiosira and Skeletonema under active upwelling conditi ons. Towar ds the en d of austral spring, a decreasing proportion of attac hed sporangia was accompanied by a decline in abundance of Skeletonema and Thalassiosira and the predominance of Chaetoceros, suggesting specificity and host density dependence of chytrid infection. The new findings on fungal parasitism of diatoms provide further support for the inclusion of Fungi in the current model of the role played by the marine microbial community in the coastal ocean. We propose a conceptual model where Fungi contrib ute to controlling the dynamics of phytoplankton populations, as well as the release of organic matter and the transfer of organic carbon th rough the pelagic trophic web in coastal upwelling ecosystems.