Abstract:Dimethyl sulfide (DMS) is an important biological sulfide in the ocean that can alleviate global warming. Dimethylsulfoniopropionate (DMSP) is the DMS precursor and mainly exists in phytoplankton. Filter-feeding bivalves are an important ecological group in coastal ecosystems, and their phytoplankton feeding activities may affect the production of dimethyl sulfide. In this study, four common economic filter- feeding bivalves, the Pacific oyster Crassostrea gigas, blue mussel Mytilus edulis, Zhikong scallop Chlamys farreri, and manila clam Ruditapes philippinarum were selected as experimental subjects, and fed them on the microalgae Isochrysis galbana with higher dimethylsulfoniopropionate (DMSP) contents. Variations of dimethyl sulfide (DMS) and DMSP in the water under static and disturbance conditions were monitored in a laboratory simulation experiment, and the effects of DMS(P) release from bivalve feces were analyzed. The results showed that the bivalves'feeding activities on phytoplankton had no significant effect on the release of DMS (P>0.05) under static conditions, but the concentration of DMSPp was significantly reduced by biodeposition (P<0.05), ~40% of the DMSPp intake was converted to fecal DMSP (DMSPf). DMSPf diffused into the water under disturbance conditions, and increased the concentrations of total suspended DMSP (DMSPt) and DMS. The disturbance experiment of total original water revealed that compared to the control group (0 r/min), the DMS and DMSPt in the treatment group, can increased up to 16.8% and 38.5% respectively. Further disturbance experiment of quantitative fecal found that the DMS and DMSPt concentrations in 1 L of seawater containing 0.08 g of feces increased following disturbance. DMS and DMSPt increased from 7.6 nmol/L and 906.4 nmol/L (static condition) to a maximum of 21.3 nmol/L and 2 505.9 nmol/L (disturbance condition), representing increases of 180% and 174%, respectively. This study contributes to a better understanding of how bivalves' feeding activities influence the marine sulfur cycle, the follow-up research can be extended to the field enclosure experiment and aquaculture area investigation.
