Seasonal and long-term community patterns in temperate marine planktonic protists

15th Symposium on Aquatic Microbial Ecology (SAME15), 3-8 September 2017, Zagreb, CroatiaProtists are recognized as fundamental components of marine ecosystems, contributing to phytoplankton biomass, primary production and food-web interactions. However, their long-term dynamics are poorly understood and, in particular, we know little on how predictable is the assembly and disassembly of their communities in temperate zones featuring annual climate cycles. Here, we analysed a long-term time-series in order to determine the patterns of community dynamics in a model protist assemblage. We carried out a monthly sampling of the picoplankton (0.2-3 µm) and nanoplankton (3-20 µm) during 10 years in the Blanes Bay Microbial Observatory (coastal North Western Mediterranean). The taxonomic composition of both assemblages was determined by Illumina sequencing the V4 region of the 18S rDNA gene. We found that the community showed two recurrent states, corresponding to summer and winter months, and two transition states corresponding to spring and autumn, being the winter communities more similar through the different years. Furthermore, we designed a `Seasonality Index¿ that allowed us to identify the seasonal taxa and quantify the strength of their seasonality. We identified that 13.2% of the OTUs (39.3% abundance) and 20.6% of the taxonomic Classes (35.2% abundance) showed seasonality and among them we could differentiate two clear behaviors (wave or pulse). Finally, we also identified seasonality in permanently rare taxa. In summary, the analysed protist community showed a recurrent annual pattern generated by their seasonal abundant members. Furthermore we identified multiple behaviors (common-rare, seasonal-no seasonal, wave-pulse) within the assemblagePeer Reviewe