Seasonal variation in the community distribution of protists off Wakasa Bay, Southern Sea of Japan

There is a dearth of knowledge regarding the spatiotemporal distribution of protistan community composition and seasonal environmental changes. High-throughput sequencing of the 18S rRNA gene was performed to assess changes in the community composition of protists over four seasons at four sites in Wakasa Bay, located in the center of Japan's northern coast. The community composition varied seasonally rather than geographically, even among few local communities confined to the bay head. Throughout the year, Alveolata and Chlorophyta were widely distributed and represented the predominant groups. Groups I and II of Syndiniales and Dinoflagellata were significant taxa in terms of operational taxonomic unit richness and sequence read abundance. Although three lineages of prasinophyte Clade VII, Pycnococcus-related prasinophyte, and Ostreococcus-related Mamiellophyceae were common, prasinophyte Clade VII was dominant during summer–autumn, whereas others were dominant during winter and spring. These results indicate the differential dominance of Chlorophyta at the intrataxon level. In the protistan community, increased temperature exerted an effect on the summer–autumn composition, whereas increased nitrate concentration showed an effect on the winter composition, suggesting that seasonal environmental changes affect the protistan community composition with different fluctuation patterns being observed among taxa. •18S rRNA gene based HTS was analyzed in Wakasa Bay.•Season specific protistan community was detected.•Syndiniales group I and II and Chlorophyta were dominated.•Different taxa of Chlorophyta showed season specific dominance.•Temperature, nitrate and salinity were effective parameters on protistan community change.