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Abstract: Temporal variation of Synechococcus, picoeukaryote and heterotrophic bacteria abundance and depth integrated biomass during three spring blooms in 2007 and 2009 were investigated in the Yellow Sea, China. Synechococcus and picoeukaryote responded differently to different types and course of spring blooms. During the diatom blooms of 2007 and Bloom B20 in 2009, Synechococcus and picoeukaryote abundances decreased sharply during the bloom period. However, during a mixed dinoflagellate and diatom bloom of Bloom B23 in 2009, Synechococcus and picoeukaryote increased in abundance and biomass along the bloom. During all three spring blooms, heterotrophic bacteria biomass had a similar increasing trend. Ciliate and heterotrophic nanoflagellate grazing could be responsible for Synechococcus and picoeukaryote abundance and biomass decrease during the spring blooms. [Copyright &y& Elsevier]

In early spring, a hydrological front emerges in the central Yellow Sea, resulting from the intrusion of the high temperature and salinity Yellow Sea Warm Current (YSWC). The present study, applying phytoplankton pigments and flow cytometry measurements in March of 2007 and 2009, focuses on the biogeochemical effects of the YSWC. The nutrients fronts were coincident with the hydrological front, and a positive linear relationship between nitrate and salinity was found in the frontal area. This contrast with the common situation of coastal waters where high salinity values usually correlate with poor nutrients. We suggested nutrient concentrations of the YSWC waters might have been enhanced by mixing with the local nutrient-rich waters when it invaded the Yellow Sea from the north of the Changjiang estuary. In addition, our results indicate that the relative abundance of diatoms ranged from 26% to 90%, showing a higher value in the YSCC than in YSWC waters. Similar distributions were found between diatoms and dinoflagellates, however the cyanobacteria and prasinophytes showed an opposite distribution pattern. Good correlations were found between the pigments and flow cytometry observations on the picophytoplankton groups. Prasinophytes might be the major contributor to pico-eukaryotes in the central Yellow Sea as similar distributional patterns and significant correlations between them. It seems that the front separates the YSWC from the coastal water, and different phytoplankton groups are transported in these water masses and follow their movement. These results imply that the YSWC plays important roles in the distribution of nutrients, phytoplankton biomass and also in the community structure of the central Yellow Sea. [ABSTRACT FROM AUTHOR]

Abstract: Bacterial community structures associated with a spring phytoplankton bloom were investigated using denaturing gradient gel electrophoresis (DGGE) and 16S rDNA clone libraries. Statistical and phylogenetic analyses applied on both molecular methods revealed differences in bacterial community composition between the bloom station and post-bloom station, as well as between two bloom stages (bloom- and decay-) at bloom station. At the class level, the bacterial community at the bloom station was dominated by Alphaproteobacteria, Flavobacteria and Gammaproteobacteria, whereas Alphaproteobacteria and Gammaproteobacteria were dominant at the post-bloom station. At order level, no obvious predominant subgroup was found at the post-bloom station. In contrast, predominant subgroups were observed in bloom samples and they changed over the course of bloom. Rhodobacterales (mainly Roseobacter) and Flavobacteriales (mainly Flavobacterium) were the predominant subgroups in the bloom period, whereas Roseobacter became the unique predominant subgroup in the decay-bloom period. Rhodobacterales and Flavobacteriales, which were dominant in the bloom-associated bacterial communities in the Yellow Sea, were also reported as dominant during bloom conditions in other ocean regions, suggesting that they play an important role in bloom events. [Copyright &y& Elsevier]