Effects of coastal shellfish farming and hypoxic stress on DMS production

Abstract Dimethylsulfide (DMS) plays an important role in the sulfur biogeochemical cycle and cloud formation on Earth. In the past few decades, coastal shellfish breeding facilities have developed rapidly and the number of hypoxic environments has increased rapidly in shallow coastal areas. However, the effects of hypoxia and marine animal feeding on DMS production remain controversial. The Yantai offshore area is an important shellfish breeding area where hypoxia occurs frequently in the bottom seawater during the summer. In this study, we found that particle dimethylsulfoniopropionate (DMSPp) and attached bacteria play dominated roles in DMS production and average DMS concentration in coastal shellfish farming region was 38.84% higher than that in non-shellfish farming region during the breeding period. Different from the zooplankton “sloppy feeding”, the shellfish “filter-feeding” first repackages the phytoplanktonic DMSP into fecal DMSP, and then degrades DMSPp into DMS by attracting attached bacteria. Based on field investigations and hypoxia simulation experiment, we found that hypoxic stress had no significant effect on the production or consumption of DMS in seawater and the decline rates of DMS at the sediment-water interface between the oxic and hypoxic groups were nearly identical. Therefore, no significant difference in average DMS concentration was observed between the mild hypoxic area and the other sea areas during the summer. Meanwhile, although the DMSP-degrading bacteria presented different responses to hypoxia, little difference was observed in the entire microbial community structure or the DMSP catabolizing genes.