Monthly Variations in the Intracellular Nutrient Pools of Phytoplankton in Jaran Bay, Korea

Abstract

It is important to understand intracellular nutrient pools of phytoplankton as a major nutrient remover in coastal areas. The water samples for intracellular nutrient concentrations (ammonium, nitrite + nitrate, phosphate, and silicate) of different sizes phytoplankton and nutrient conditions in ambient water column were monthly obtained in a southern coastal area of Korea, Jaran Bay from February to December 2016. The intracellular nutrients of phytoplankton were extracted by the method of osmotic shock combined with heating. The intracellular nutrient concentrations during this study were 0.35-1.79, 0.19-12.63, 0.01-0.40, and 0.549.21 mu M for ammonium, nitrite + nitrate, phosphate, and silicate, respectively. In comparison, the water column nutrient concentrations were 0.26-12.00, 0.05-14.39, 0.002-1.26, and 1.43-48.33 mu M for ammonium, nitrite + nitrate, phosphate, and silicate, respectively. The contributions of micro-sized (> 20 mu m) phytoplankton and pico-sized (0.7-2 mu m) phytoplankton accounted for 48.2% and 22.7% of the total chlorophyll a concentration, respectively in this study. The intracellular nutrient concentration per unit of chlorophyll a concentration had a negative relationship with the chlorophyll contribution of micro-sized phytoplankton. This result suggests that larger phytoplankton are appeared to store less intracellular nutrient pools than smaller phytoplankton. This is related to the characteristics of dominant phytoplankton species in Jaran Bay such as Chaetoceros debilis and Chaetoceros affinis which normally accumulate small amounts of intracellular nutrients compared to small phytoplankton. Based on this result, nutrient dynamics in marine ecosystems especially for coastal areas would be different under ongoing larger contributions of small phytoplankton in warming ocean conditions.