Characterization of Seasonal Phytoplankton Pigments and Functional Types around Offshore Island in the East/Japan Sea, Based on HPLC Pigment Analysis

Abstract

In this study, we investigated the seasonal phytoplankton community and phytoplankton functional types (PFTs) in the vicinity of Dokdo Island, located in the East/Japan Sea, in 2019. With strong seasonal winds, the water column was well mixed in winter. In spring and autumn, the upper mixed layer depth (MLD) was relatively deep, and the Subsurface Chlorophyll Maximum (SCM) formed in the middle layer. Small phytoplankton were dominant in the summer, which is a time of high water temperatures and strong stratification associated with a shallower MLD. Based on CHEMTAX analysis, in spring, the high phytoplankton biomass was mainly derived from cyanobacteria, diatoms, and dinoflagellates. In summer, >73.2% of the surface biomass was comprised of cyanobacteria. In autumn, pelagophytes accounted for the highest proportion of the biomass. The fraction of microphytoplankton (fmicro) was highest in winter and spring, whereas the fraction of nanophytoplankton (fnano) was highest in autumn and summer. A high fraction of picophytoplankton (fpico) was evident in the surface layers in summer. Values for both the photoprotection index (PI) and the ratio of photoprotective carotenoids (PPC) to photosynthetic carotenoids (PSC) indicate that this study area had high primary productivity in 2019. In order to predict long-term changes in marine food webs due to climate change, it is important to evaluate the size and composition of phytoplankton.

Estimation of Phytoplankton Size Classes in the Littoral Sea of Korea Using a New Algorithm Based on Deep Learning

“…However, previous studies on phytoplankton communities in the East Sea reported differences in the dominant communities depending on the study period and survey station [41][42][43][44][45]. An observation shared among most of these studies is that the size of the key dominant size of the phytoplankton communities tends to decrease as the water temperature increases after spring [41,[43][44][45]. According to the observations of phytoplankton communities in the South Sea and East China Sea from January to May, micro-size phytoplankton are dominant in the west, whereas pico-size phytoplankton are dominant in the central region.…”

“…According to prior research, the key dominant size of phytoplankton communities in spring (March-April) in the East Sea are micro-size diatoms [38][39][40]. However, previous studies on phytoplankton communities in the East Sea reported differences in the dominant communities depending on the study period and survey station [41][42][43][44][45]. An observation shared among most of these studies is that the size of the key dominant size of the phytoplankton communities tends to decrease as the water temperature increases after spring [41,[43][44][45].…”

“…From June to September, pico-size phytoplankton showed high distributions in all the sea areas (Figures 3-5). In summer (June-August) when strong stratification develops, pico-size phytoplankton are the dominant size in the littoral sea at surface depths (East, West, South, and East China Seas) [37,44,45,[47][48][49]. However, certain studies conducted in the South Sea observed that the contribution of nano-size phytoplankton or micro-size phytoplankton were high [19,50].…”

Impact of Complex Oceanographic Features on Seasonal Phytoplankton Community and Biodiversity from 2018 to 2020 in the Vicinity of Dokdo (Island), Offshore Korea

“…The Korea Institute of Ocean Science and Technology (KIOST) has been conducting studies in the Ulleung Basin, including Ulleungdo and Dokdo, as a hub for systematic research in marine physics, chemistry, and biology since 2000. While some studies have explored the response of phytoplankton to physical characteristics in the Ulleung Basin [8,15,16], as well as phytoplankton population dynamics and photosynthetic pigments around Ulleungdo and Dokdo [17][18][19], most of these investigations have been limited to short-term studies, and there has been a lack of periodic research centered around Dokdo. However, it is not easily accessible and is subject to the influences of weather and wave conditions that can change rapidly in the waters around Dokdo due to its unique geographical and oceanographic attributes.…”

Summer Distributional Characteristics of Surface Phytoplankton Related with Multiple Environmental Variables in the Korean Coastal Waters

“…The average water depth of the East Sea is 1700 m, but it has deep basins exceeding 2500 m in depth. The East Sea has a well-defined sub-polar front at approximately 37-40 • N [7]. This front is created between a warm water mass from the East Korea Warm Current (EKWC), which branches from the Tsushima Warm Current (TWC), and a cold water mass from the North Korea Cold Current (NKCC), a branch of the Liman Current.…”