• Ocean and Polar Research
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• v.32 no.1
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• pp.1-13
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• 2010

To assess short-term variation of summer phytoplankton community structure in different water masses, phytoplankton and environmental factors were monitored from 31 stations on and off the southern coasts of Korea, from June 18 to June 20 2009. According to multidimensional scaling (MDS) and cluster analysis based on phytoplankton community data from each station, the southern sea was divided into two groups. The first group included stations in the south-eastern region of Jeju Island, which is strongly influenced by the Kuroshio warm current. The second group located along the coastal region of the southern sea, which was mainly comprised of Bacillariophyceae and Crytophyceae. Of these stations, St. 13 and 28 formed a temperature front caused by different hydrological conditions. In particular, nutrients and Chl.a concentrations in these two stations were significantly higher compared to those in the other stations. This indicates that phytoplankton population and subsequent microalgal growth under high nutrient concentrations vary in different water masses. Our results support the theory that phytoplankton community structure in the southern sea of Korea can be influenced on a short-term scale by different water masses and currents.

• Ocean and Polar Research
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• v.46 no.2
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• pp.105-121
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• 2024

Phytoplankton, as key primary producers, play a critical role in the dynamics of marine ecosystems. This study explores the variation in phytoplankton species appearance along the Jeju coast from spring to summer 2022, emphasizing the stratification and changes in nutrient dynamics. Through extensive field surveys at twelve points around Jeju Island, we measured a range of physical and chemical oceanographic parameters. Monthly average stratification indices displayed an abrupt increase from 22 in May to 3,196 in August, highlighting intense stratification, significantly influenced by the influx of Changjiang River Diluted Water during the summer months. Concurrently, nutrient concentrations exhibited a downward trend, with nitrate and nitrite levels decreasing from 6.7 µM in March to 1.3 µM in July, and phosphate levels declining from 0.31 µM to 0.02 µM during the same period, while silicate concentrations, ranging from 6.8 to 9.8 µM, remained consistently high throughout the study. Similarly, a reduction in monthly average phytoplankton biomass was observed, with concentrations peaking in the spring (April and May) at 406,053 to 409,139 cells L^-1 and declining to 45,546 to 118,214 cells L^-1 by summer (June to August). Diatoms (Chaetoceros spp. and Skeletonema spp.) dominated the phytoplankton community throughout the period; however, an increased proportion of dinoflagellates (Gyrodinium spp. and Heterocapsa spp.) was observed during the summer months, when stratification was most pronounced. This study confirms that variations in currents and water masses impacting the Jeju coast can significantly influence phytoplankton community dynamics, emphasizing the need for ongoing monitoring in this region.

• Journal of Environmental Science International
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• v.20 no.10
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• pp.1243-1263
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• 2011

This study was carried out to determine marine environments and phytoplankton community in Deukryang Bay during the period of summer in 1987-2010. Water temperature, salinity, pH and dissolved oxygen were shown in much yearly fluctuations. In August, water temperatures in surface and on bottom were the highest, compared with average surface (24.54$^{\circ}C$) and bottom (22.90$^{\circ}C$) water temperature for 18 years in Deukryang Bay. The main reason is assumed to longer duration of sunshine during the period of August. Although the amount of the rainfall in August was the highest, significant impact of marine environment did not show. Most of dissolved inorganic nitrogen and phosphate in Deukryang were lower concentration during summer and N:P ratio also showed below 18 in Redfield. In particular, extreme increasing of N:P ratio in August was occurred by intensive precipitation. Distribution of phytoplankton community was a consistent occurrence for 18 years. The genus of Chaetoceros, Cosinodisucs and Skeletonema were regarded as the represent diatom, whereas the highest occurrence of genus among dinofagellates was Ceratium. It is thought that the relationship between phytoplankton and nutrient has a strong positive signal, although nutrients persist a little concentration and much fluctuations in marine environments were observed. High availability in phytoplankton is contributed to consistently provide the food organism of shellfish. Consequently, recent decreasing production of shellfish and seed are probably associated with higher temperature during the period of summer. However, higher temperature is also occurred ago and after 2000. On the basis of geography, Deukryang Bay had a small mouth and long channel, which is attributed to decreasing genetic diversity. It is assumed that higher temperature and lower genetic diversity have a extreme impact of larvae and shellfish for reproduction in Deukryang. It is necessary to persistently monitor based on water quality and phytoplankton community.

• Ocean and Polar Research
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• v.33 no.4
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• pp.457-472
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• 2011

To elucidate the trophic role of heterotrophic nano- and microplankton (HNMP), we investigated their biomass, community structure, and herbivory in three different water masses, namely, south of Polar Front (SPF), Polar Front Zone (PFZ), the Sub-Antarcitc Front (SAF) in the Drake Passage in the Southern Ocean, during the austral summer in 2002. We observed a spatial difference in the relative importance of the dominant HNMP community in these water masses. Ciliates accounted for 34.7% of the total biomass on an average in the SPF where the concentration of chlorophyll-a was low with the dominance of pico- and nanophytoplankton. Moreover, the importance of ciliates declined from the SPF to the SAF. In contrast, heterotrophic dinoflagellates (HDFs) were the most dominant grazers in the PFZ where the concentration of chlorophyll-a was high with the dominance of net phytoplankton. HNMP biomass ranged from 321.9 to 751.4 $mgCm^{-2}$ and was highest in the PFZ and lowest in the SPF. This result implies that the spatial dynamic of HNMP biomass and community was significantly influenced by the composition and concentration of phytoplankton as a food source. On an average, 75.6%, 94.5%, and 78.9% of the phytoplankton production were consumed by HNMP in the SPF, PFZ, and SAF, respectively. The proportion of phytoplankton grazed by HNMP was largely determined by the composition and biomass of HNMP, as well as the composition of phytoplankton. However, the herbivory of HNMP was one of the most important loss processes affecting the biomass and composition of phytoplankton particularly in the PFZ. Our results suggest that the bulk of the photosynthetically fixed carbon was likely reprocessed by HNMP rather than contributing to the vertical flux in Drake Passage during the austral summer in 2002.

• Ocean and Polar Research
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• v.32 no.2
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• pp.97-111
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• 2010

Phytoplankton production is affected by various physico-chemical factors of environment. However, one of the most critical factors generally accepted as controlling primary production of phytoplankton is nutrients. It has recently been found that the succession of phytoplankton groups and species are closely related to the chemical properties of ambient water including nutrient limitation and their ratios. In Jangmok Bay, silicate and nitrate are primarily supplied by rainfall, while phosphate and ammonia are supplied by wind stress. Typhoons are associated with rainfall and strong wind stress, and when typhoons pass through the South Sea, such events may induce phytoplankton blooms. When nutrients were supplied by heavy rainfalls during the rainy season and by summer typhoons in Jangmok Bay, the dominant taxa among the phytoplankton groups were found to change successively with time. The dominant taxon was changed from diatoms to flagellates immediately after the episodic seasonal events, but returned to diatoms within 3~10 days. Pseudo-nitzschia spp. were dominant mainly in the presence of low phosphate levels during the first of the survey which included the rainy season, while Skeletonema costatum was dominant when phosphate concentrations were high due to the strong wind stress during the latter half of the survey as a result of the typhoon. The competition between S. costatum and Chaetoceros spp. appeared to be regulated by the silicate concentration. S. costatum preferred high silicate and phosphate concentrations; however, Chaetoceros spp. were able to endure low silicate concentrations. These results implied that, in coastal ecosystems, the input patterns of each nutrient supplied by rainfall and/or wind stress appeared to contribute to the summer succession of phytoplankton groups and species.

• Journal of Environmental Science International
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• v.21 no.3
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• pp.313-326
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• 2012

Three embankments, namely Changpo, Bokkil and Guil, in Chunggye Bay were investigated to assess the influence of environmental changes to phytoplankton size structure, distribution of species and standing crops. Three stations was sampled near at each embankment in Nov. 2006, Feb. 2007, May 2007 and Aug. Phytoplankton were classified into net-size (>20${\mu}m$) and nano-size (<20${\mu}m$). In summer, the freshwater discharge seemed to have influence in the decrease of salinity and in the increase of turbidity, ammonium and phosphorus concentrations. Chl a concentration and phytoplankton abundance in Feb. 2007 were observed to be generally higher in all stations compared to other periods. Net-size phytoplankton was observed to be higher in Feb. 2007 and May 2007 compared to nano-sized phytoplankton. However, there was shift in phytoplankton composition in Nov. 2006 and Aug. 2007. Phytoplankton under seven class (Bacillariophyceae, Chlorophyceae, Chrysophyceae, Cryptophyceae, Cyanophyceae, Dinophyceae, Euglenophyceae) was identified during the study period. It was found out that the major phytoplankton class was Bacillariophyceae. Phytoplankton was more diverse in autumn compared to any other season. Cyanophyceae was increased in summer. In rainy season, change in physical factors (salinity, transparency) seemed to have more influence on phytoplankton growth compared to inorganic nutrients.

• Journal of Environmental Science International
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• v.18 no.1
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• pp.21-32
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• 2009

The short-term variations of the mesozooplankton community structure were investigated in Gamak Bay during summer season, 2006. The study was based on a comprehensive survey constituting from 12 stations on June 19, July 28, August 4, and August 29, respectively. Mean of temperature and chlorophyll ${\alpha}$ concentrations in the surface layer were significantly higher than those in bottom layer, and those concentrations were significantly higher in the inner bay than those in the outer bay. A total of 40 taxa including 19 copepods were observed in Gamak Bay during summer season. Mean abundance of total mesozooplankton varied from 1,859 to 26,111 indiv. $m^{-3}$. The dominant species were Noctiluca scintillans, Penilia avirostris, Evadne tergestina, Paracalanus parvus s. 1., Acartia omorii and Cirriped nauplii and cyprii in Gamak Bay, and they contributed 90% of mean abundance of total mesozooplankton. Noctiluca scintillans was high after the rainfall. Cluster analysis showed that the mesozooplankton community could be divided into 4 distinct groups, indicating rapid change of the community in the short-term of this survey. The relative contribution of each group of the N. scintillans, P. avirostris, E. tergestina, and P. parvus s. 1. showed differences during the phytoplankton bloom period. The mesozooplankton community compositions were highly associated with water temperature, and salinity in physical conditions, and food organisms affect short-term variations in mesozooplankton composition. Interestingly, protozoa N. scintillans, and Cladocera appeared to be one of the key organisms to extinguish the phytoplankton bloom. Therefore, this study suggests that N. scintillans, and Cladocera could be a key player to control the mesozooplankton community structure during summer season, 2006.

• Korean Journal of Environmental Biology
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• v.21 no.2
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• pp.132-141
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• 2003

We carried out a study on thermohaline structure and phytoplankton com munity in the East China Sea during early summer in 2005. As a result of marine environment and phytoplankton community, three characteristics of water type were identified. The former was characterized by the dominant species with diatoms, Chaetoceros lacinious, Ch. decipiens, Guninardia flaccida, Paralia sulcata, Pseudonitzschia pungens and Pseudosolenia calcar-avis in Chinese coastal waters, the secondary was done by lower water temperature, salinity and the dominant species with dinoflagellates, Prorocentrum donghaiense and Ceratium fusus, in over-all areas and the latter was done by the dominant species with coastal species of diatoms, Skeletonema costafum and Nitzschia longissima and silicoflagellate, Dictyocha speculum var. octopers in the transfer areas of Chinese continental coastal waters. Phytoplankton community in the surface layer identified a total of 66 species belonging to 36 genera. Dominant species was Prorocentrum donghaiense, Chaetoceros lacinious, Skeletonema costatum. Standing crops of phytoplankton in the surface layer flue tuated between $1.5 \times 10^4$cells $L^{-1}$ and $3.5\times 10^{5}$ cells $L^{-1}$. And the highest value appeared in the Changjiang estuaries with high dominance by diatoms and lowest one occurred in the southwestern area of Jeju Island with high dominance by dinoflagellates. Red tides with dinoflagellate, Prororcentrum donghaiense appeared in the frontal areas with mazimum cell density, $3.4\times 10^5$ cells $L^{-1}$. And outbreak environments was low water temperature under $20^{\circ}C$, and low salinity under 31.55 psu. The vertical distribution of red tide organisms went to about 30m depth from surface.

• Ocean and Polar Research
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• v.34 no.2
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• pp.111-123
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• 2012

To understand the phytoplankton community in the eastern part of the Yellow Sea (EYS), in the summer, field survey was conducted at 25 stations in June 2009, and water samples were analyzed using a epifluorescence microscopy, flow cytometry and HPLC method. The EYS could be divided into four areas by a cluster analysis, using phytoplankton group abundances: coastal mixing area, Anma-do area, transition water, and the central Yellow Sea. In the coastal mixing area, water column was well mixed vertically, and phytoplankton was dominated by diatoms, chrysophytes, dinoflagellates and nanoflagellates, showing high abundance ($>10^5\;cells\;l^{-1}$). In Anma-do coastal waters characterized by high dominance of dinoflagellates, high phytoplankton abundance and biomass separated from other coastal mixing area. The southeastern upwelling area was expanded from Jin-do to Heuksan-do, by a tidal mixing and coastal upwelling in the southern area of Manjae-do, and phytoplankton was dominated by benthic diatoms, nanoflagellates and Synechococcus group in this area. Phytoplankton abundance and biomass dominated by pico- and nanophytoplankton were low values in the transition waters and the central Yellow Sea. In the surface of the central Yellow Sea, high dominance of photosynthetic pigments, 19'-hexanoyloxyfucoxanthin and zeaxanthin implies that haptophytes and cyanobacteria could be the dominant group during the summer. These results indicate that the phytoplankton communities in the EYS were significantly affected by the formation of tidal front, thermal stratification, and coastal upwelling showing the differences of physical and chemical characteristics during the summer.

• Ocean and Polar Research
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• v.31 no.1
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• pp.71-76
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• 2009

Drastic changes in the water quality and phytoplankton community of the new Saemankeum Lakeduring the first decade following the construction of the Saemankeum Sea Wall has been considered to be unavoidable. Input of eutrophicated water through the Mankyeong River and Dongjin River might produce more direct effects on the water quality and phytoplankton community, which lead us to launch a long-term semi-weekly investigation at the "Mankyeong Bridge" monitoring point to resolve its short-term effect as well as long-term stabilization of the ecosystem in the new Saemankeum Lake. During 15 months starting from June 2006, the water temperature varied in accordance with the typical seasonal variations in temperate on the coasts, and no significant daily variations evoked by tidal cycle could be detected. However, there was an inverse relationship between seasonal precipitation and salinity even though the range in annual variation was drastically reduced right after the construction of the Saemankeum Sea Wall. Species richness in the phytoplankton community was also reduced due to the narrowed annual range of salinity, which would eliminate the mid-high salinity species from the Mankyeong Bridge monitoring point. Similarly, species diversity was decreased with increased dominance of the phytoplankton community after the construction. Between the two summer seasons during the present study, species diversity was higher in 2007 than in 2006, which might indicate the early stage of a gradual stabilization in the ecosystem including the phytoplankton community at the monitoring station. The phytoplankton community thus needs to be monitored on a long-term basis to identify indirect signals that can be used to assess the stability of the ecosystem in the young Saemankeum Lake.