In the estuarine environment, the freshwater discharge regulated by the sea dike influences the planktonic ecosystem as an anthropogenic stressor. Particularly, the freshwater discharge events are mostly concentrated in summer rainy season in the Northeast Asia countries, rapidly altering phytoplankton composition in estuary. In this study, we aimed to understand the variations in diet utilization of zooplankton under rapid changes in phytoplankton community triggered by freshwater discharge event using nitrogen isotope ratio of amino acids in the Yeongsan River estuary (Korea), which has a dike to control freshwater use. In result, freshwater discharge events increased concentrations of inorganic nitrogen and altered size-fractionated chlorophyll-a composition. In addition, nitrogen isotope ratios of both POM and particle-feeding zooplankton near the sluice gate increased close to those in downstream freshwater within two days, implying the nitrogen source in discharged freshwater is rapidly reflected to organisms in estuarine planktonic ecosystem. The trophic position of particle-feeding zooplanktons did not show any significant difference during episodic freshwater discharge event except for Acartia after two days near sea dike, likely due to their wide availability on particle size and origin. This study results suggest particle-feeding zooplankton have a high adaptability on diet utilization in rapidly changing environment by the regulated freshwater discharge in the estuarine environment.

Primary Presenter: Hyuntae Choi, Hanyang University (dmb122@hanyang.ac.kr)

Authors:

Sehee Kim, Mokpo National Maritime University  ()

Jinhee Wi, Research Institute for Coastal Environment and Fishery-policy  ()

Yongsik Sin, Mokpo National Maritime University  ()

Kyung-Hoon Shin, Hanyang University  ()