The Effect of Zooplankton on the Distributions of Dimethyl Sulfide and Dimethylsulfoniopropionate in the Bohai and Yellow Seas

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.

Automated summary

This study investigated the spatial distributions of DMS, DMSP, DLA, and the abundances of bacteria, DMSP-consuming bacteria, and dimethyl sulfoxide-consuming bacteria in the surface seawater of the Bohai Sea and Yellow Sea during autumn 2020. The results showed that the distributions of DMS and dissolved DMSP were significantly correlated with DLA. Grazing by microzooplankton promoted the conversion of DMSP to DMS, and mesozooplankton copepod grazing stimulated DMS production.