Thijs Frenken, Elisabet Alacid, Stella A. Berger, Elizabeth Charlotte Bourne, Melanie Gerphagnon, Hans-Peter Großart, Alena S. Gsell, Bas W. Ibelings, Maiko Kagami, Frithjof C. Kupper, Peter M. Letcher, Adeline Loyau, Takeshi Miki, Jens C. Nejstgaard, Serena Rasconi, Albert Rene, Thomas Rohrlack, Keilor Rojas-Jimenez, Dirk S. Schmeller, Bettina Scholz, Kensuke Seto, Telesphore Sime-Ngando, Assaf Sukenik, Dedmer B. Van de Waal, Silke Van den Wyngaert, Ellen Van Donk, Justyna Wolinska, Christian Wurzbacher, Ramsy Agha

• Chytridiomycota, often referred to as chytrids, can be virulent parasites with the potential to inflict mass mortalities on hosts, causing e.g. changes in phytoplankton size distributions and succession, and the delay or suppression of bloom events. Molecular environmental surveys have revealed an unexpectedly large diversity of chytrids across a wide range of aquatic ecosystems worldwide. As a result, scientific interest towards fungal parasites of phytoplankton has been gaining momentum in the past few years. Yet, we still know little about the ecology of chytrids, their life cycles, phylogeny, host specificity and range. Information on the contribution of chytrids to trophic interactions, as well as co-evolutionary feedbacks of fungal parasitism on host populations is also limited. This paper synthesizes ideas stressing the multifaceted biological relevance of phytoplankton chytridiomycosis, resulting from discussions among an international team of chytrid researchers. It presents our view on the most pressing research needs forChytridiomycota, often referred to as chytrids, can be virulent parasites with the potential to inflict mass mortalities on hosts, causing e.g. changes in phytoplankton size distributions and succession, and the delay or suppression of bloom events. Molecular environmental surveys have revealed an unexpectedly large diversity of chytrids across a wide range of aquatic ecosystems worldwide. As a result, scientific interest towards fungal parasites of phytoplankton has been gaining momentum in the past few years. Yet, we still know little about the ecology of chytrids, their life cycles, phylogeny, host specificity and range. Information on the contribution of chytrids to trophic interactions, as well as co-evolutionary feedbacks of fungal parasitism on host populations is also limited. This paper synthesizes ideas stressing the multifaceted biological relevance of phytoplankton chytridiomycosis, resulting from discussions among an international team of chytrid researchers. It presents our view on the most pressing research needs for promoting the integration of chytrid fungi into aquatic ecology.…