대한해협에서 수층 혼합에 의한 영양염 특성의 변화가 식물플랑크톤 군집 구조에 미치는 영향

Abstract

In the western of Korea Strait, the controlling factors on the distribution of nutrient are the intrusion of water mass such as TCWW, ESCW, and KSBCW, consumption of phytoplankton, seasonal mixing, and wind mixing by typhoon. Under the stratified condition of water column, the rich nutrients supplied from TCWW and KSBCW were not available for phytoplankton growth. However, during the period that the shelf water was strongly mixed through typhoon invasions and winter mixings, the reserved nutrients reached the euphotic zone and then affected in the phytoplankton biomass and their community structure. The main factor encouraging the biomass increase of phytoplankton was the enhanced stability of water mass rather than the increased temperature because the warm current of TCWW is always flowing in the western of Korea Strait. Under the low nutrient conditions and in the earlier upwelling periods which is characterized by strong mixing, small phytoplankton is dominant. However, under the replete nutrient conditions or in the initially stabilized water column, micro phytoplankton was dominant in the study area. The supply of abundant nutrient below the stratified layer by seasonal mixing and wind mixing of typhoon induced the phytoplankton succession from flagellate to diatom, and consequent low nutrient condition, which is especially silicate limited, led to the succession from diatom to flagellate in the end of the mixing periods and typhoon. The two species, Chaetoceros socialis and Skeletonema costatum, differed in their responses to the nutrient property. Chaetoceros spp. was dominant in the condition of low nutrient and high N:P ratios, whereas S. costatum favored high nutrient and lower N:P ratio in the mixing periods. The most dominant diatom species was Chaetoceros spp. during the survey periods in the study area, which shows a high N:P ratio due to low background concentration of phosphate and frequent phosphate limitation. The dominance of Leptocylindrus danic