Distinct oxygen environments shape picoeukaryote assemblages thriving oxygen minimum zone waters off central Chile

Oxygen minimum zones (OMZs) support ocean biogeochemical cycles of global importance. The OMZ off central Chile is characterized by seasonally variable oxygen concentrations due to upwelling events. Bacterial and archaeal communities from this area have been previously described; however, picoeukaryote communities remain largely unexplored. In order to improve our knowledge on picoeukaryote ecology and the effect of controlling factors on its community structure, environmental parameters and 18S rRNA metabarcoding analyses were performed in water samples collected at several depths at a time series station on the continental shelf in March, May and August. Our results showed that oxygen, nitrate, silicate and temperature are relevant factors shaping the picoeukaryote community structure. Overall, according to our sequence dataset, the OMZ was dominated by Dinophyceae members including marine parasitic dinoflagellates. Moreover, dysoxic and suboxic conditions were enriched by fungi and phagotrophic protists from Ustilaginomycetes, Bicoecea and Choanoflagellatea. The latter is particularly relevant in the understanding of metazoan evolution and the origins of multicellularity in low-oxygen environments. Picoeukaryote communities changed significantly over the 3 months sampled with variations in water column stratification, including the occurrence of a winter bloom of Mamiellales. Altogether, this study reveals a great diversity and dynamics of picoeukaryotes inhabiting a coastal OMZ.