Role of Calanus sinicus (Copepoda, Calanoida) on Dimethylsulfide and Dimethylsulfoniopropionate Production in Jiaozhou Bay

The role of copepod Calanus sinicus on the production of dimethylsulfide (DMS)/dimethylsulfoniopropionate (DMSP) in Jiaozhou Bay was evaluated in field measurements and laboratory experiments. Samples at 10 sites in the bay were collected monthly from June 2010 to May 2011 (except for March 2011), and zooplankton species composition was analyzed. Effects of C. sinicus grazing on DMS/DMSP production at different conditions (i.e., algal diets, food concentrations, and salinities) were assessed in the laboratory. Data from the field experiment showed that C. sinicus was the dominant copepod in Jiaozhou Bay (up to 123 individuals/m(3) in May 2011) and preferred to graze on diatom. DMS and DMSP concentrations depend on not only phytoplankton abundance but also phytoplankton species and bacterial abundance. In the laboratory experiment, compared with Gymnodinium sp. or Emiliania huxleyi, C. sinicus feeding on Isochrysis galbana and Chaetoceros curvisetus exhibited increased DMS concentration, whereas high salinity inhibited DMS production. Copepod ingested 0.5%-35% of DMSP in filtered phytoplankton, and copepod DMSP ingestion turnover rate in Jiaozhou Bay was up to 29 pmol L-1 d(-1). Although the microbial DMSP consumption rate was 10-2,620-fold of copepod turnover rate, copepod grazing was still one of the important routes in DMSP loss processes through food chain. This study indicated that DMSP was transferred from phytoplankton to copepod body, fecal pellet, and seawater through copepod grazing. Our results provided important information to understand the biogeochemical cycle of DMSP in Jiaozhou Bay. Plain Language Summary Dimethylsulfide (DMS) is the most abundant biogenic sulfur gas that may influence planetary climate by forming cloud condensation nuclei that alters global radiation balance. Role of copepod Calanus sinicus grazing on DMS production in Jiaozhou Bay were investigated in this study. From the results of in situ study, we found that C. sinicus was the dominant copepod in Jiaozhou Bay, and DMS and dimethylsulfoniopropionate (DMSP) concentrations were related to abundance and species of phytoplankton and zooplankton, and bacterial abundance. Therefore, four algae were used as the diets of C. sinicus to assess the C. sinicus grazing on DMS production. The effects of diet concentration and salinity on feeding rate of C. sinicus and DMS concentration were also investigated. The results showed that C. sinicus preferred to graze on poor-dimethylsulfoniopropionate algae, and low salinity facilitated DMS production. Dimethylsulfoniopropionate transfer from algae to copepod body and fecal pellet through food chain were also evaluated. The results were helpful to understand the role of copepod on sulfur cycle and further the whole world climate.