동해 남부해역에서 냉수대 발생이 식물플랑크톤 군집에 미치는 영향

Abstract

The influence of upwelling events on phytoplankton community was studied at 18 stations located southern part of East Sea, Korea from May to August 2013. The surface water masses showed low temperature and high salinity due to upwelling events at coastal stations (A1, B1, C1). The characters of water masses could be defined the mixed water of Tsushima Middle Water (TMW) and North Korean Cold Water (NKCW). Phytoplankton communities were composed of 195 species, among which diatoms predominated during the study period. Phytoplankton abundance were relatively high in May(station C1, 726×103 cells L-1) and July (station A1, 539 ×103 cells L-1). The most dominant species were Leptocylindrus danicus (May), Psuedo-nitzschia spp. (June), Chaetoceros curvisetus (July) and Cochlodinium polykrikoides (August) at coastal stations (A1, B1, C1) during the study period. In particular, after the appearance of C. polykrikoides at outside stations in July, C. polykrikoides known to be a harmful algae was dominant at coastal stations in August. Total Chl-a and micro-size fraction (>20 μm) increased at coastal stations in July and August. Also, large-size species that have bio-volume over 20,000 μm3 increased slightly at this time. Correlation between temperature and nutrients (DIP, r=-0.218, p<0.01, n=141; DIN, r=-0.306, p<0.01, n=141; silicate, r=-0.274, p<0.01, n=141) was significantly negative. This result could be explained that nutrients were supplied to surface water by upwelling of bottom water. Therefore, the increase in total Chl-a and size of phytoplankton was resulted in the sufficient supply of nutrients. In contrast, these tendencies were not observed at outside stations. These results suggested that coastal upwelling was an important influencing factor to determine the species composition and standing stock of phytoplankton community in the coastal waters of southern East Sea, Korea.