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Dimethyl sulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) are ubiquitous sulfur compounds in the ocean. DMS is emitted into the atmosphere and has potential climatic effects. The distributions of DMS and DMSP are affected by various biological factors (i.e., bacterial catabolism and phytoplankton and zooplankton community composition). The horizontal and vertical distributions of DMSP, DMSP lyase activity (DLA), DMS, and the abundances of bacteria, DMSP‐consuming bacteria, dimethyl sulfoxide‐consuming bacteria, and picophytoplankton were investigated in the Bohai Sea (BS) and Yellow Sea (YS) during autumn 2020. DLA was significantly correlated with chlorophyll a, DMS, and dissolved DMSP concentrations. Our data show that bacteria Clade_I SAR11 was a significant contributor to DLA. A dilution experiment indicated that the highest microzooplankton grazing rate coincided with the highest DMS concentration and DMS production rate. A proportion of 16%–62% of the DMSPt was converted to DMS in the dilution experiment. Copepods dominated the mesozooplankton community. Calanus sinicus was the predominant copepod in the BS and YS. C. sinicus grazing stimulated DMS production. DMS concentration increased 299% after C. sinicus grazing on physically broken algal cells for 48 hr. These results will help with a better understanding of the control of DMS and DMSP concentrations by zooplankton and the DMS release mechanisms that occur through zooplankton grazing. Plain Language Summary: Dimethylsulfoniopropionate (DMSP) and dimethyl sulfide (DMS) are transferred and transformed in the food web and are affected by zooplankton, phytoplankton, and bacteria. This study investigated spatial distributions of DMS, DMSP, DMSP lyase activity (DLA), the abundances of bacteria, DMSP‐consuming bacteria, and dimethyl sulfoxide‐consuming bacteria in the surface seawater of the Bohai Sea and Yellow Sea. As results, the distributions of DMS and dissolved DMSP were significantly correlated with DLA. A deck incubation experiment indicated that grazing by microzooplankton promoted the conversion of DMSP to DMS and that mesozooplankton copepod grazing stimulated DMS production. These results provide a more comprehensive way to understand the possible DMS release mechanisms via zooplankton grazing. Key Points: Dimethyl sulfide (DMS) concentration was significantly correlated with dimethyl sulfoxide‐consuming bacterial abundanceMicrozooplankton grazing consumed 4%–7% of the total dimethylsulfoniopropionate daily and 16%–62% was converted to DMSCopepod ingestion stimulated DMS production, which increased by 299% at 48 hr in physically broken algal cells [ABSTRACT FROM AUTHOR]

Effects of elevated CO_2 (5000μl/L) on sensitivity comparison of six species of algae and interspecific competition of three species of algae were investigated. The results showed that, the cell densities of six species of algae grown in elevated CO_2 significantly increased compared to those in ambient CO_2 (360μl/L), and with the time prolonged, the increasing extent increased. Therefore, elevated CO_2 can promote the growth of six species of algae. However, there were differences in sensitivity between six species of algae. Based on the effects of elevated CO_2 on biomass, the sensitive order (from high to low) was Platymanas sp., Platymanas subcordiformis, Nitzschia closterium, Isochrysis galbana Parke 8701, Dunaliella salina, Chlorella sp., on the condition of solitary cultivation. Compared to ambient CO_2, elevated CO_2 promoted the growth of three species of algae, Platymanas subcordiformis, Nitzschia closterium and Isochrysis galbana Parke 8701 under the condition of mixed cultivation. The sensitivity of the three species to elevated CO_2 in mixed cultivation changed a lot compared to the condition of solitary cultivation. When grown in elevated CO_2 under the condition of mixed cultivation, the sensitive order from high to low were Nitzschia clostertium, Platymonas subcordiformis and Isochrysis galbana Parke 8701. However, under the condition of solitary cultivation, the sensitive order in elevated CO_2 was Isochrysis galbana Parke 8701, Nitzschia clostertium, Platymonas subcordiformis, from sensitive to less sensitive. On the day 21, the dominant algae, the sub-dominant algae and inferior algae grown in elevated CO_2 did not change. However, the population increasing dynamic and composition proportion of three algal species have significantly changed. [ABSTRACT FROM AUTHOR]