The Ecosystem of the Southern Coastal Waters of the East Sea, Korea I. Phytoplankton Community Structure and Primary Productivity in September, 1994

Phytoplankton community and primary productivity have been investigated in a fall season in the southern coastal waters of the last Sea, Korea. A strong thermocline formed at the layer and a cold water mass also existed in the bottom around Yong-il Bay. The offshore of the surveyed area was likely to be influenced by relatively warmer water, whereas the inshore represented Higher primary productivity with lower water temperature and lower salinity. A total of 133 species of phytoplankton occurred, representing 107 spp. of diatom, 23 spp. of dinoflagellate 3 spp. of silicoflagellate. Skeletonema costatum and Asterionellepsis glacialis were most predominant with more than dominance ratio, while Leptocylindrus danicus was also dominant at all transect lines. Standing crops of phytoplankton ranged from . Chlorophyll a concentration varied with stations and layers, but the m layer showed maximun with about rather than at the surface layer. It is believed that the maximun in standing crops and chlorophyll of phytoplankton formed at the m layer above the thermocline during the survey. Phytoplankton primary productivity ranged from 0.32 to 3.04 mgC , showing higher at the inshore than at the offshore. The range of integrated primary productivity was for the euphotic layer. Photosysthesis rates varied with the range from 0.76 to 8.04 mgC mgChl . Phytoplankton photosynthesis at the inshore was saturated at lower irradiance ( of surface) and showed higher efficiency, Thus, it revealed that the phytoplankton community probably adapted to the middle of euphotic layer because the depth of mixing layer became thinner due to the formation of thermocline.