Introduction

Diatoms are a successful and ubiquitous phytoplankton group with over 200,000 species. They range in size from µms to mms and exist either as single cells or as chains of connected cells (Kooistra, et al. 2007). These silica-depositing microalgae have been abundant for more than 180 million years (Falkowski, et al. 2004); they contribute 40% of the total oceanic primary production and ~20% of global primary production (Field, et al. 1998), and annual diatom photosynthesis reportedly generates approximately as much organic carbon as all rainforests combined (Field, Behrenfeld, Randerson and Falkowski 1998, Nelson, et al. 1995). Diatoms in coastal waters support the most productive fisheries, and in the open ocean, they sink rapidly from the surface to become food for deep-water organisms (Sarthou, et al. 2005). Thus, diatoms are crucial contributors to the global carbon cycle and have even been considered as a potential solution for reducing atmospheric CO2 levels (Denman 2008). Given their ubiquitous nature, diatoms are logical subjects for researchers interested in global ecological trends such as climate change, as foreseen in the concept that “everything is everywhere, but the environment selects” ((Finlay 2002). Changes in diatom community diversity can be considered to be indicative of adaptation occurring in response to selective pressures.
The Korean Peninsula is surrounded by the Yellow Sea (YS), the Southern Sea (SS; also known as Korean coastal waters connected to the East China Sea), and the East Sea (ES, or the Sea of Japan), each with its distinguishing characteristics. The YS, located between mainland China and the Korean Peninsula, is a shallow (generally < 100 m), post-glacially submerged, epicontinental sea with one of the largest continental shelves in the world (Wang, et al. 2003). The SS is subjected to Kuroshio currents and receives outflows from the Changjiang River, which is among the world’s largest rivers (Ichikawa and Beardsley 2002). Also bordering Japan and Russia, the ES is a typical, mid-latitude, marginal sea, approximately the size of the western Mediterranean and is somewhat unusual in exhibiting characteristics typical of both closed basins and oceans. Similarities to the former are due to its sill depths of < 150 m which limits seawater exchange with the North Pacific Ocean. ES also contains oceanic deep basins (> 3000 m), large (> 15℃) seasonal variations in sea surface temperatures, and highly active biological processes and exhibits a sub-arctic polar front between its sub-polar and sub-tropical seas (Kim, et al. 2001).
Diatom communities tend to dominate in well-mixed coastal and upwelling regions, as well as along sea-ice edges where sufficient light, inorganic nitrogen, phosphorus, silicon, and trace elements are available to sustain their growth (Morel and Price 2003). Therefore, the purpose of the present study is to investigate the diversity and distribution of diatom communities in the coastal areas of South Korea through a winter survey of 114 sampling sites and to clarify links to sea characteristics using diatom community cluster analysis.