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Global warming and climate change are increasingly affecting the frequency and intensity of typhoons. The vertical mixing induced by typhoons enhances the availability of nutrients, subsequently influencing phytoplankton and prokaryotic ecology. However, research on the effects of typhoons on the ecology of phytoplankton and prokaryotes in the Yellow Sea (YS) is limited. This study examined the variations in phytoplankton and prokaryotic communities in response to typhoon-induced disturbances by comparing data from the YS in August 2020 (affected by Typhoon Bavi) with data from the typhoon-free period in August 2022. Post-typhoon observations revealed a decrease in water temperature and an increase in salinity within the surface mixed layer. Significantly higher concentrations of chlorophyll-a and pigments such as peridinin, fucoxanthin, alloxanthin, and chlorophyll-b were recorded in 2020, indicating an increase in phytoplankton biomass and shifts in its composition. Although prokaryotic heterotrophic production increased at most stations following the typhoon, changes in prokaryotic abundance and composition were less evident with only minor increases observed in Verrucomicrobiales and Euryarchaeota, potentially because of insufficient time for bacterial growth to manifest in increased abundance. Overall, the changes in phytoplankton and prokaryotic communities resembled those observed during the spring bloom, suggesting that typhoons can temporarily shift the pelagic ecosystem toward a bloom state during summer. [ABSTRACT FROM AUTHOR]

The presence of zooplankton in marine ecosystems is an important factor affecting toxin production in dinoflagellates. However, whether the production of paralytic shellfish toxins (PSTs) by Gymnodinium catenatum and Alexandrium pacificum is affected by substances produced by zooplankton is not yet fully understood. This study assessed the effects of zooplankton extracts on cell abundance, pigment concentration and composition, chlorophyll-a-specific primary production (Chl-a SP), and PST production in G. catenatum and A. pacificum, isolated from Korean coastal waters. In addition, a novel group of hydroxybenzoate PSTs known as GC toxins, which lack commercial reference standards, was evaluated. No significant differences were observed in cell abundance, pigment composition, or Chl-a SP in the experimental group of G. catenatum strains exposed to zooplankton extracts compared to the control group. However, the production of PSTs, including GC toxins, was significantly enhanced when the strain was exposed to extracts of Calanus finmarchicus. Meanwhile, in the A. pacificum strain, some experimental groups showed significant differences in cell abundance and pigment composition, while Chl-a SP significantly decreased in all experimental groups. In addition, PST production was stimulated by the addition of C. finmarchicus extracts. No GC toxins were detected in the A. pacificum strain. This study demonstrated that substances derived from C. finmarchicus enhance the production of PSTs in G. catenatum and A. pacificum. Our findings will improve the current understanding of the occurrence and development mechanisms of PSTs in marine ecosystems and contribute to developing strategies to efficiently secure standard reference toxin products using toxic dinoflagellates. [ABSTRACT FROM AUTHOR]

The Yellow Sea is one of the world's most abundant marine resources, providing food and economic benefits to the Korean and Chinese populations. In spring 2020, a decrease in the intensity of phytoplankton bloom was observed. While one study attributed this decline to a decrease in nutrient associated with the COVID-19 pandemic, our previous research proposed weakened thermal stratification accompanied by a surface cooling anomaly as the cause. However, the relationship between the marine environment and ecosystem has not been fully elucidated. Using observations and marine physical-biogeochemical model data, we identified the weakened stratification as a critical factor for suppressing the 2020 spring bloom. Intense vertical mixing hindered the accumulation of nutrient and chlorophyll-a concentrations within the euphotic zone, resulting in a diminished phytoplankton bloom. In contrast, reduced nitrate and phosphate concentrations in 2020 were insignificant compared to those in 2017–2019, despite the notable decline in PM2.5 in March 2020 due to COVID-19. In April 2020, nutrient levels fell within the range of interannual variability based on long-term observations, reflecting a negligible effect on the spring phytoplankton bloom. Our findings provide insight into the importance of marine physical factors on the phytoplankton biomass in the Yellow Sea. [ABSTRACT FROM AUTHOR]

The Yellow Sea is one of the world's most abundant marine resources, providing food and economic benefits to the Korean and Chinese populations. In spring 2020, a decrease in the intensity of phytoplankton bloom was observed. While one study attributed this decline to a decrease in nutrient associated with the COVID-19 pandemic, our previous research proposed weakened thermal stratification accompanied by a surface cooling anomaly as the cause. However, the relationship between the marine environment and ecosystem has not been fully elucidated. Using observations and marine physical-biogeochemical model data, we identified the weakened stratification as a critical factor for suppressing the 2020 spring bloom. Intense vertical mixing hindered the accumulation of nutrient and chlorophyll-a concentrations within the euphotic zone, resulting in a diminished phytoplankton bloom. In contrast, reduced nitrate and phosphate concentrations in 2020 were insignificant compared to those in 2017–2019, despite the notable decline in PM2.5 in March 2020 due to COVID-19. In April 2020, nutrient levels fell within the range of interannual variability based on long-term observations, reflecting a negligible effect on the spring phytoplankton bloom. Our findings provide insight into the importance of marine physical factors on the phytoplankton biomass in the Yellow Sea. [ABSTRACT FROM AUTHOR]

The CHEMTAX program has been widely used to estimate community composition based on major pigment concentrations in seawater. However, because CHEMTAX is an underdetermined optimization algorithm, underdetermined bias has remained an unsolved problem since its development in 1996. The risk of producing biased results increases when analyzing the picophytoplankton community; therefore, this study tested a new method for avoiding biased CHEMTAX results using the picophytoplankton community around the East Sea (Japan Sea). This method involves building a linear model between pigment concentration data and community composition data based on DNA sequencing to predict the pigment range for each operational taxonomic unit, based on the 95% prediction interval. Finally, the range data are transformed into an initial ratio and ratio limits for CHEMTAX analysis. Three combinations of initial ratios and ratio limits were tested to determine whether the modeled initial ratio and ratio limit could prevent underdetermined bias in the CHEMTAX estimates; these combinations were the modeled initial ratio and ratio limit, the modeled initial ratio with a default ratio limit of 500 s, and an initial ratio from previous research with the default ratio limit. The final ratio and composition data for each combination were compared with Bayesian compositional estimator-based final ratio and composition data, which are robust against underdetermined bias. Only CHEMTAX analysis using the modeled initial ratio and ratio limit was unbiased; all other combinations showed significant signs of bias. Therefore, the findings in this study indicate that ratio limits and the initial ratio are equally important in the CHEMTAX analysis of biased datasets. Moreover, we obtained statistically supported initial ratios and ratio limits through linear modeling of pigment concentrations and 16s rDNA composition data. [ABSTRACT FROM AUTHOR]

Tintinnid ciliates, having distributional sensitivity to hydrological changes, have been applied as a useful tool to track the movements of water masses. The Yellow Sea Bottom Cold Water (YSBCW) is one of the most prominent summer oceanographic phenomena in the Yellow Sea. To examine the potential of tintinnid species as a biological indicator of the bottom cold water, the spatial distributions of the ciliates were investigated in the southeastern Yellow Sea during the summers of 2010 and 2020. A dominant species, Tintinnidium primitivum, was found in the bottom cold waters in both years. The temperature and salinity (T–S) diagram for the dominant species distribution was plotted against the T–S range for the YSBCW at low temperatures between 6 and 12 ℃ and salinity between 32 and 33. A positive relationship was shown between T. primitivum and Gammaproteobacteria distribution and negative relationships with photosynthetic pico- and nano-plankton. Further studies on prey and predator relationships between microbial organisms and T. primitivum are required to understand the unique structure and function of microbial food webs in the YSBCW. [ABSTRACT FROM AUTHOR]