• Ocean and Polar Research
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• v.30 no.3
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• pp.289-301
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• 2008

Community structure of heterotrophic protists and their grazing impact on phytoplankton were studied in Northwest Pacific Ocean during October, 2007. The study area was divided into four regions based on physical properties (temperature and salinity) and chlorophyll-a distribution. They were Region I of North Equatorial Currents, Region II of Kuroshio waters, Region III of shelf mixed water, and Region IV of Tsushima warm current from East China Sea. The distribution of chlorophyll-a concentrations and community structure of heterotrophic protists were significantly affected by physical properties of the water column. The lowest concentration of chlorophyll-a was identified in Region I and II, where pico-sized chlorophyll-a was most dominant (>80% of total chlorophyll-a). Biomass of heterotrophic protists was also low in Region I and II. However, Region III was characterized by low salinity and temperature and high chlorophyll-a concentration, with relatively lower pico-sized chlorophyll-a dominance. The Highest biomass of heterotrophic protists appeared in Region III, along with the relatively less important nanoprotists. In Region I, II and IV, heterotrophic dinoflagellates were dominant among the protists, while ciliates were dominant in Region III. Community structure varied with physical(salinity and temperature) and biological (chlorophyll-a) properties. Biomass of heterotrophic protists correlated well with chlorophyll-a concentration in the study area ($r^2=0.66$, p<0.0001). The potential effect of grazing activity on phytoplankton is relatively high in Region I and II. Our result suggest that biomass and size structure of heterotrophic protists might be significantly influenced by phytoplankton size and concentration.

• Ocean and Polar Research
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• v.26 no.4
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• pp.567-579
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• 2004

To investigate the spatial distribution and community structure of heterotrophic protists, we collected water samples at 23 stations of central Barents Sea in August, 2003. This study area was divided into three area with physico-chemical and chi-a distribution characteristics: Area I of warm Atlantic water mass, Area III of cold Arctic water mass and Area II of mixed water mass. Chl-a concentration ranged from 0.18 to $1.04{\mu}g\;l^{-1}$ and was highest in Area I. The nano-sized chi-a accounted fur more than 80% of the total chi-a biomass in this study area. The contribution of nano-sized chi-a to total chi-a was higher in Area I than in Area II. Communities of heterotrophic protists were classified into three groups such as heterotrophic nanoflagellates (HNF), ciliates and heterotrophic dinoflagellates (HDF). During the study periods, carbon biomass of heterotrophic protists range from 11.3 to $38.7{\mu}gC\;l^{-1}$ (average $21.0{\mu}gC\;l^{-1}$), and were highest in Area I and were lowest in Area III. The biomass of ciliates ranged from 4.2 to $19.3{\mu}gC\;l^{-1}$ and contributed 31.5-66.9% (average 48.1%) to the biomass of heterotrophic protists. Ciliates to heterotrophic protists biomass accounted fur more than 50% in Area I. Heterotrophic dinoflagellates biomass ranged from 5.7 to $18.4{\mu}gC\;l^{-1}$ and contributed 27.1 to 56.3% (average 42.8%) of heterotrophic protists. Heterotrophic dinoflakellates to heterotrophic protists biomass accounted fur about 50% in Area III. Heterotrophic nanoflageltate biomass ranged from 0.5 to $3.4{\mu}gC\;l^{-1}$ and contributed 3.2 to 19.6% (average 9.2%) of heterotrophic protists. Heterotrophic nanoflagellates to heterotrophic protists biomass accounted fur more than 10% in Area III. These results indicate that the relative importance and structure of heterotrophic protists may vary according to water mass. Heterotrophic protists and phytoplankton biomass showed strong positive correlation in the study area The results suggest that heterotrophic protists are important consumers of phytoplankton, and protists might play a pivotal role in organic carbon cycling In the pelagic ecosystem of this study area during the study period.

• Ocean and Polar Research
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• v.29 no.4
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• pp.401-410
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• 2007

In Korea the study of marine heterotrophic protists started in the late 1980s, and since the early 1990s many studies have been conducted in various marine environments. In this article, studies on the distribution and abundance of protists and the biotic interactions(bacteria-protists, phytoplankton-protists) conducted in Korean coastal waters are reviewed, and a field study is reported and discussed. The field study in Masan Bay was carried out from February 2004 to November 2005 at seven selected stations representative of the bay. During the study, the mean abundance of heterotrophic bacteria and the mean concentration of chlorophyll-a were $2.1{\times}10^6\;cells\;mL^{-1}$ and $9.8{\mu}g\;L^{-1}$, respectively. Heterotrophic protists consisted of heterotrophic dinoflagellates, heterotrophic nanoflagellates(excluding dinoflagellates) and ciliates, and their abundances were means of $7.9{\times}10^4\;cells\;L^{-1}$, $1.2[\times}10^3\;cells\;mL^{-1}$, and $4.0{\times}10^4\;cells\;L^{-1}$, respectively. Generally, the chlorophyll-a concentra+CZ14tions and the abundances of heterotrophic bacteria and protists were higher in the inner zone of the bay, where there are high concentrations of organic matters, than in the middle and outer zones. Using the grazing rates of heterotrophic nanoflagellates on bacteria previously reported in this area, it can be calculated that about 69% of bacterial producton was removed by HNF grazing activity. About 24% of initial chlorophyll-a concentration was removed by microzooplankton grazing activity. In conclusion, this study suggests that in Masan Bay heterotrophic protists control the growth of bacteria and phytoplankton, and heterotrophic protists represent an important link of bacterial & microalgal biomass to higher trophic levels.

• Journal of the korean society of oceanography
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• v.35 no.1
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• pp.46-55
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• 2000

In order to understand the role of heterotrophic protists in the coastal waters off Inchon, abiotic and biotic factors were measured from January 1992 to February 1993. Microbial carbon biomass (mean212.9$^{\pm}$119.1 $^{\mu}$gC/1) was composed of 4.2% bacteria, 0.3% cyanobacteria, 12.l% autotrophic nanoflagellates, 6.6% heterotrophic nanoflagellates, 5.8 heterotrophic ciliates and 71.0% diatom and Mesodinium spp. The carbon biomass of heterotrophic protists (heterotrophic nanoflagellates and ciliates) was highest in October 1992 (mean 37.8$^{\pm}$22.5 $^{\mu}$gC/1), and was low in August 1992 (mean 21.2$^{\pm}$10.8 $^{\mu}$gC/1) and in February 1993 (mean 19.5$^{\pm}$6.4 $^{\mu}$gC/1). However, the contribution of heterotrophic protists to total microbial carbon biomass was higher in January 1992 and February 1993 (about 21%) when the phytoplankton was dominated by nanoplankton than in August and October (about 9%) when large diatoms occurred in large numbers. This study suggests that in Kyeonggi Bay heterotrophic protists might play a more important role as prey for zooplankton and as consumers of bacteria & small phytoplankton in less productive seasons (especially winter) than in productive seasons (autumn), and that the classic trophic pathway from diatoms through copepods to fish might be dominant nearly every season.

• ALGAE
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• v.32 no.4
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• pp.309-324
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• 2017

Recently, the heterotrophic nanoflagellate Katablepharis japonica has been reported to feed on diverse red-tide species and contribute to the decline of red tides. However, if there are effective predators feeding on K. japonica, its effect on red tide dynamics may be reduced. To investigate potential effective protist predators of K. japonica, feeding by the engulfment-feeding heterotrophic dinoflagellates (HTDs) Oxyrrhis marina, Gyrodinium dominans, Gyrodinium moestrupii, Polykrikos kofoidii, and Noctiluca scintillans, the peduncle-feeding HTDs Luciella masanensis and Pfiesteria piscicida, the pallium-feeding HTD Oblea rotunda, and the naked ciliates Strombidium sp. (approximately $20{\mu}m$ in cell length), Pelagostrobilidium sp., and Miamiensis sp. on K. japonica was explored. We found that none of these heterotrophic protists fed on actively swimming cells of K. japonica. However, O. marina, G. dominans, L. masanensis, and P. piscicida were able to feed on heat-killed K. japonica. Thus, actively swimming behavior of K. japonica may affect feeding by these heterotrophic protists on K. japonica. To the contrary, K. japonica was able to feed on O. marina, P. kofoidii, O. rotunda, Miamiensis sp., Pelagostrobilidium sp., and Strombidium sp. However, the specific growth rates of O. marina did not differ significantly among nine different K. japonica concentrations. Thus, K. japonica may not affect growth of O. marina. Our findings suggest that the effect of predation by heterotrophic protists on K. japonica might be negligible, and thus, the effect of grazing by K. japonica on populations of red-tide species may not be reduced by mortality due to predation by protists.

• ALGAE
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• v.32 no.3
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• pp.199-222
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• 2017

Occurrence of Cochlodinium polykrikoides red tides have resulted in considerable economic losses in the aquaculture industry in many countries, and thus predicting the process of C. polykrikoides red tides is a critical step toward minimizing those losses. Models predicting red tide dynamics define mortality due to predation as one of the most important parameters. To investigate the roles of heterotrophic protists in red tide dynamics in the South Sea of Korea, the abundances of heterotrophic dinoflagellates (HTDs), tintinnid ciliates (TCs), and naked ciliates (NCs) were measured over one- or two-week intervals from May to Nov 2014. In addition, the grazing impacts of dominant heterotrophic protists on each red tide species were estimated by combining field data on red tide species abundances and dominant heterotrophic protist grazers with data obtained from the literature concerning ingestion rates of the grazers on red tide species. The abundances of HTDs, TCs, and NCs over the course of this study were high during or after red tides, with maximum abundances of 82, 49, and $35cells\;mL^{-1}$, respectively. In general, the dominant heterotrophic protists differed when different species caused red tides. The HTDs Polykrikos spp. and NCs were abundant during or after C. polykrikoides red tides. The mean and maximum calculated grazing coefficients of Polykrikos spp. and NCs on populations of co-occurring C. polykrikoides were $1.63d^{-1}$ and $12.92d^{-1}$, respectively. Moreover, during or after red tides dominated by the phototrophic dinoflagellates Prorocentrum donghaiense, Ceratium furca, and Alexandrium fraterculus, which formed serial red tides prior to the occurrence of C. polykrikoides red tides, the HTDs Gyrodinium spp., Polykrikos spp., and Gyrodinium spp., respectively were abundant. The maximum calculated grazing coefficients attributable to dominant heterotrophic protists on co-occurring P. donghaiense, C. furca, and A. fraterculus were 13.12, 4.13, and $2.00d^{-1}$, respectively. Thus, heterotrophic protists may sometimes have considerable potential grazing impacts on populations of these four red tide species in the study area.

• Ocean and Polar Research
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• v.26 no.2
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• pp.113-120
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• 2004

The abundance, biomass and distribution of phytoplankton, bacterioplankton and heterotrophic protists in the Bering Sea were investigated from July to August 1999. Chlorophyll a concentrations in the surface waters ranged from 0.16 to $3.79{\mu}g\;l^{-1}$ Nano-phytoplankton were found to constitute from 63 to 98% of the total phytoplankton biomass, and were clearly the dominant primary producers. The biomass of bacterioplankton in the surface layers varied from 1.46 to $20.2{\mu}g\;C\;l^{-1}$ and accounted for 30% of the total phytoplankton biomass. The biomass of bacterioplankton integrated over a depth of 0 to 100m averaged 65.4% of the total phytoplankton biomass. The surface biomass of heterotrophic protists ranged from 1.2 to $27.4{\mu}g\;C\;l^{-1}$, and was within the same order of magnitude as that of bacterioplankton. Of the total biomass of heterotrophic protists in the upper 100m of the water column, 65% was attributed to protists in the nano-size class. The results of this study suggest that bacteria and nano-protists are important components of the planktonic community in the Bering Sea during the summer season. The abundance of bacterioplankton and planktonic protists decreased from the western to northeastern and eastern regions of the Bering Sea. The abundance of these organisms also decreased with depth. The available evidence suggests that variation in the abundance and distribution of these organisms may be affected by water currents and vertical temperature variation in the Bering Sea.

• ALGAE
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• v.36 no.1
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• pp.25-36
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• 2021

The mixotrophic dinoflagellate Tripos furca causes red tides in the waters of many countries. To understand its population dynamics, mortality due to predation as well as growth rate should be assessed. Prior to the present study, the heterotrophic dinoflagellates Noctiluca scintillans, Polykrikos kofoidii, Protoperidinium steinii, and mixotrophic dinoflagellate Fragilidium subglobosum were known to ingest T. furca. However, if other common heterotrophic protists are able to feed on T. furca has not been tested. We explored interactions between T. furca and nine heterotrophic dinoflagellates and one naked ciliate. Furthermore, we investigated the abundance of T. furca and common heterotrophic protists in coastal-offshore waters off Yeosu, southern Korea, on Jul 31, 2020, during its red tide. Among the tested heterotrophic protists, the heterotrophic dinoflagellates Aduncodinium glandula, Luciella masanensis, and Pfiesteria piscicida were able to feed on T. furca. However, the heterotrophic dinoflagellates Gyrodiniellum shiwhaense, Gyrodinium dominans, Gyrodinium jinhaense, Gyrodinium moestrupii, Oblea rotunda, Oxyrrhis marina, and the naked ciliate Rimostrombidium sp. were unable to feed on it. However, T. furca did not support the growth of A. glandula, L. masanensis, or P. piscicida. Red tides dominated by T. furca prevailed in the South Sea of Korea from Jun 30 to Sep 5, 2020. The maximum abundance of heterotrophic dinoflagellates in the waters off Yeosu on Jul 31, 2020, was as low as 5.0 cells mL-1, and A. glandula, L. masanensis, and P. piscicida were not detected. Furthermore, the abundances of the known predators F. subglobosum, N. scintillans, P. kofoidii, and Protoperidinium spp. were very low or negligible. Therefore, no or low abundance of effective predators might be partially responsible for the long duration of the T. furca red tides in the South Sea of Korea in 2020.

• ALGAE
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• v.34 no.2
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• pp.127-140
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• 2019

The species in the dinoflagellate order Suessiales have 5-24 latitudinal paraplate series and include many fossil and extant species. There have been a few studies on the ecophysiology of the phototrophic species Biecheleriopsis adriatica, and no study on its predators. Thus, we explored the feeding occurrence by common heterotrophic protists on B. adriatica and the growth and ingestion rates of the heterotrophic dinoflagellate Oxyrrhis marina on B. adriatica BATY06 as a function of prey concentration. The common heterotrophic dinoflagellates Aduncodinium glandula, O. marina, Gyrodinium dominans, Gyrodinium moestrupii, Luciella masanensis, Pfiesteria piscicida, and Oblea rotunda and two naked ciliates Strombidinopsis sp. and Pelagostrobilidium sp. were able to feed on B. adriatica, but the heterotrophic dinoflagellate Polykrikos kofoidii was not. However, B. adriatica supported the positive growth of O. marina, but did not support that of G. dominans and O. rotunda. With increasing prey concentrations, the growth and ingestion rates of O. marina on B. adriatica increased and became saturated. The maximum growth rate of O. marina on B. adriatica was $0.162d^{-1}$. Furthermore, the maximum ingestion rate of O. marina on B. adriatica was $0.2ng\;C\;predator^{-1}\;d^{-1}$ ($2.0cells\;predator^{-1}\;d^{-1}$). In the order Suessiales, the feeding occurrence by common heterotrophic protists on B. adriatica is similar to that on Effrenium voratum and Biecheleria cincta, but different from that on Yihiella yeosuensis. However, the growth and ingestion rates of O. marina on B. adriatica are considerably lower than those on E. voratum and B. cincta, but higher than those on Y. yeosuensis. Therefore, B. adriatica may be less preferred prey for O. marina than E. voratum and B. cincta, but more preferred prey than Y. yeosuensis.

• Journal of Microbiology and Biotechnology
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• v.19 no.9
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• pp.858-868
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• 2009

The abundance, biomass, size distribution, and taxonomic composition of bacterial and protistan (heterotrophic and autotrophic nanoflagellates and ciliates) communities were investigated in six lakes of Masurian Lake District (north-eastern Poland) differing in trophic state. Samples were taken from the trophogenic water layer during summer stratification periods. Image analysis techniques with fluorescent in situ hybridization (FISH) as well as [$^3H$]-methyl-thymidine incorporation methods were applied to analyze differences in the composition and activity of bacterial communities. The greatest differences in trophic parameters were found between the humic lake and remaining non-humic ones. The same bacterial and heterotrophic nanoflagellate (HNF) cell size classes dominated in all the studied lakes. However, distinct increases in the contributions of large bacterial (>$1.0{\mu}m$) and HNF (>$10{\mu}m$) cells were observed in eutrophic lakes. The bacterial community was dominated by the ${\beta}$-Proteohacteria group, which accounted for 27% of total DAPI counts. Ciliate communities were largely composed of Oligotrichida. Positive correlations between bacteria and protists, as well as between nanoflagellates (both heterotrophic and autotrophic) and ciliates, suggest that concentrations of food sources may be important in determining the abundance of protists in the studied lakes.