Effects of Harpacticus sp. (Harpacticoida, copepod) grazing on dimethylsulfoniopropionate and dimethylsulfide concentrations in seawater

Abstract

We conducted 9d and 24h ingestion experiments to investigate the effects of copepod grazing on the concentrations of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) in seawater. Data from the 9d trial showed that copepod Harpacticus sp. (Harpacticoida, copepod) grazing increased DMS (0–20%) and dissolved DMSP (DMSPd) (0–128%) apparently, accompanied by a significant reduction of particulate DMSP (DMSPp) in algal culture (0–30%). Ingestion rates (IRs) and pellet production rates (PPRs) of Harpacticus sp. varied with diet species (Platymonas subcordiformis (PS), Nitzschia closterium (NC), Skeletonema costatum (SC), Isochrysis galbana (IG), Prymnesium parvum (PP) or Heterosigma akashiwo (HA)), algal concentration, salinity and temperature. Harpacticus sp. fed on PP showed the lowest IRs (female/male, 0.72/0.53×104cells copepod−1h−1) and PPRs (female/male, 0.75/0.5 pellets copepod−1h−1), accompanied with the largest amounts of DMS and DMSPd,p (sum of DMSPd and DMSPp). IRs, PPRs, DMS and DMSPf (DMSP in fecal pellet) increased with the increase of food concentration and peaked at 25×104cellsmL−1I. galbana. High salinity decreased IRs, PPRs, DMS and DMSPf and increased DMSPz (DMSP in copepod body) and DMSPd,p. IRs, PPRs, DMS and DMSPf increased with the increase of temperature from 15 to 25°C, whereas DMSPz and DMSPd,p contents decreased. Pearson correlation analysis results showed that DMS concentrations presented positive relationships with IRs in algal concentration, salinity and temperature experiments (r=0.746; P<0.01). The contribution of DMSPz, DMSPf, DMS and DMSPd,p concentration to the total amounts (DMSPz+DMSPf+DMS+DMSPd,p) was 4–37%, 3–36%, 8–42% and 9–89%, respectively, indicating that DMSP was transferred to copepod tissue and fecal pellet via grazing. Our results are helpful for further understanding of the role of copepod grazing on DMS biogeochemical cycle.