황동중국해의 위도에 따른 초미소 식물플랑크톤의 군집구조 및 다양성 변화

Abstract

Picophytoplanktons(<2–3 μm), composed primarily of photosynthetic prokaryotes(Prochlorococcus, Synechococcus) and picoeukaryotic phytoplankton, play essential roles as primary producers in diverse marine systems. It is well known that these picophytoplankton groups are abundant in global marine environment, and Prochlorococcus spp. accounts for more than half of the total primary production in the upper layer of oligotrophic marine environment. Recent studies reported increasing trends for the biomass and contribution of picophytoplankton groups in the marine environment of the Korea Peninsula, and further investigation and attention is needed to ascertain such trend of picophytoplankton. Furthermore, the East China Sea and the Yellow Sea, major marine regimes of the Korea Peninsula, show dynamic and complex system influenced by the fluctuating strength of Taiwan Warm Current, the Yellow Sea Warm Current, the Yellow Sea Bottom Cold Water, coastal currents of Korea and China, and Kuroshio Branch Current. These different water masses varies with time and season impacting regional physical environment as well as the productivity and species composition of phytoplankton. Thus, it is essential to understand the connection between community structure and distribution of picophytoplankton and surrounding environmental characteristics. Based on the water temperature observed during the study period, seven different water masses were identified, and the community structure and diversity of picophytoplankton were analyzed for those different water masses. Synechococcus and picoeukaryotes showed high abundance and high diversity in the relatively large water masses of euphotic zone of Yellow Sea and YSCW. In thermocline formed around 30 m in the Yellow Sea also showed high biomass and high diversity despite its relatively small water mass. This suggests that the thermocline formed in the warmer season may play an important function influencing the changes in the community structure and diversity of picophytoplankton. In particular, the size-fractionated chlorophyll concentrations showed relatively high contributions to the total chlorophyll concentration which suggest that picophytoplankton possessing broad spectrum of ecophysiological characteristics are may be rich in clade/OTSs allowing them to adapt to environmental changes. In addition, the appearance of low-salinity species OTU due to the formation of low salinity in the surface water mass of the Yellow Sea due to the influence of low-salinity water in Chiangjang diluted waters suggests that an increase in summer rainfall and freshwater discharge may affect the diversity of picophytoplankton communities.