Conclusion

We have investigated diatom distribution in South Korean coastal waters in winter finding four major ecoregions (YS, SS, SES, and NES). In the YS ecoregion, the selected indicator species were characterized as tychoplanktonic and euryhaline diatoms indicating that the region had uniform water column mixing with freshwater inputs. In the SS ecoregion, the dominance of chain-forming diatoms was considered to be a response to the turbulence caused by an uneven coastline and strong tidal flows and by the Tsushima Warm Current. In the SES ecoregion, having stalk-forming diatoms such as Licmophora and Achnanthes as indicator species was thought to be associated with a simpler coastline with the strong Tsushima Warm Current limiting the distribution of planktonic species in this region. In the NES ecoregion, the Liman Cold Current was considered to be the main factor influencing diatom distribution as our analysis showed that cold-water species such asCorethron criphilum and Porosira glacialiswere its indicator species.
Although the influence of physical, chemical, and biological factors on diatom distribution was not investigated in this study, the diatom-based biogeographical groupings and their indicators species have reflected some factors that can influence the spatial distribution of diatoms in South Korean coastal waters, in winter.