Diversity of parasitic chytrids associated with dinoflagellate blooms on the Catalan coast

Abstract

To understand bloom dynamics, biological mechanisms play a key role in phytoplankton behavior. Factors such as parasitism and saprophytism can impair bloom development and enhance the decline of natural HAB populations, as well as allow the transfer of organic matter to other trophic levels. An example of this dynamics is the parasitic phytoplankton-fungi relationship. However, it is mostly unknown in the marine environment. For this reason, here, we evaluated the diversity of Chytridiomycota during blooms of 6 different dinoflagellate species occurring in several coastal locations in the NW Mediterranean Sea. For this purpose, we combined metabarcoding, microscopy observations and live cultivation of chytrids from seawater and sediment samples. Our results showed that chytrids represented an overall abundance of 1.4% in the eukaryotic community with a total of 77 amplicon sequence variants (ASVs). Furthermore, the chytrid community varied significantly among sites, mainly depending on the blooming host. The highest diversity and abundance of chytrids were found in Ostreopsis and Alexandrium blooms as well as having a higher diversity and abundance mainly in sediment compared to seawater. ASVs corresponding to the chytrid species Dinomyces arenysensis co-occurred with the dinoflagellate Ostreopsis sp. in all locations where present. Such relationship was also confirmed by lab experiments. Therefore, our results suggest a diverse and wide geographic distribution of chytrid communities during dinofagellate coastal bloom, in some cases, specific distribution of chytrids species is strongly dependent on its host distribution