대한해협에서 열층 형성이 식물플랑크톤 군집구조와 영양염제한에 미치는 영향

Abstract

The profile of a fixed site at station M (34.77 N, 129.13 E) in the Korea Strait was studied from March 2006 to February 2007 to understand the relationship between the annual pattern of thermal stratification and the seasonal variation of phytoplankton composition. Environmental factors including temperature, salinity and nutrient concentrations, which strongly influence the proliferation and diversity of phytoplankton were measured. The concentration of chlorophyll a ranged between 0.01 and 2.14 mg m-3. Higher concentrations of chlorophyll a were detected in the upper part of the thermocline during the thermal stratification between June and November 2006. The total chlorophyll a measurement was fractionized into three; pico (<3 μm), nano (3-20 μm) and microplankton (>20 μm). A chain-forming diatom, Chaetoceros socialis dominated the phytoplankton population between March and May 2006 before formation of the thermocline (0.02×105 - 11.58×105 cells l-1), while pico+nano sized phytoplankton (<10μm) overwhelmingly dominated the phytoplankton population during and just after thermal stratification between June 2006 and January 2007 (0.006×105 - 4.51×105cells l-1). Apart from pico+nano sized small organisms, the secondarily dominant phytoplankton population was dinoflagellates, such as Gyrodinium species (0.002×105 - 0.22×105 cells l-1) during thermal stratification. Chaetoceros socialis dominated the phytoplankton community again from January 2007 until the end of experiment (0.004×105 - 3.0×105 cells l-1). The mean concentration of nitrate was lower in subsurface water (<30 m) during thermal stratification (1.10 ± 0.21 μM) than that during the mixed period (3.68 ± 0.25 μM), suggesting the pico+nano sized plankton, which could be nitrogen fixers, were able to dominate the phytoplankton population due to the oligotrophic conditions in the upper layer of the thermocline. The concentrations of phosphate were depleted during thermal stratification but sili