• Journal of the Korean Society of Marine Environment & Safety
• /
• v.30 no.5
• /
• pp.396-406
• /
• 2024

We carried out a field survey to analyze the spatial distributions of phytoplankton communities at 15 stations in the Yellow Sea in 2019. Diatoms exhibited a high appearance rate in winter and spring, whereas small flagellates(<20 ㎛) showed a high appearance rate in summer and autumn. This change in the phytoplankton-community structure may be ascribed to low nutrient concentrations in the area, especially of phosphate, which was below the detection limit, seriously hampering the phytoplankton growth. The composition ratio of picophytoplankton was high in the surface mixed layer in summer and autumn when the water columns exhibited strong stratification. Redundancy analysis revealed strong negative correlations between nutrients (NO₃^-, PO₄^3-) and water depth. In conclusion, the reduction in nutrients in the surface mixed layer owing to the strengthening of stratification in summer and autumn creates favorable conditions for the growth of relatively small phytoplankton with low nutrient requirements, leading to a shift towards a smaller phytoplankton-community structure.

• Korean Journal of Environmental Biology
• /
• v.41 no.1
• /
• pp.89-100
• /
• 2023

We investigated the spatial distribution of heterotrophic bacteria associated with different water masses in the northern East China Sea(ECS) in summer. The surface water masses were divided into the Changjiang Diluted Water (CDW) and high salinity water (HSW). In the CDW region, the concentrations of dissolved inorganic nitrogen (DIN) and chlorophyll-a (Chl-a), and micro Chl-a contribution were high; and bacterial abundance (BA) and ciliate abundance (CA) were also high. In the HSW region with relatively low DIN concentrations, Chl-a concentration and micro Chl-a contribution were low, but pico Chl-a contribution was increased compared to those in the CDW region. BA did not show any significant difference from the CDW region, but CA was decreased. BA showed a positive correlation with Chl-a concentration in the CDW region; however, it did not show a significant correlation with Chl-a concentration in the HSW region. The ratio of bacterial carbon biomass/phytoplankton carbon biomass was exponentially increased with a decrease in the Chl-a concentration. Compared to the past (1990-2000s), the surface phosphate concentrations and the size of dominant phytoplankton have recently decreased in the ECS. Considering this trend of nutrient decrease and miniaturization of the phytoplankton, our results indicate that changes in the strength of the oligotrophic water mass could alter the function of the microbial food web.