A dilution approach for quantifying the grazing-mediated production of dissolved dimethylsulphoniopropionate (DMSPd) and dimethyl sulphide (DMS) was tested using laboratory cultures and in natural marine waters. We attempted to make simultaneous estimates of microzooplankton grazing rate and grazing-mediated production of DMS and DMSPd. In the laboratory, the dinoflagellate Oxyrrhis marina grazed on the prymnesiophyte Isochrysis galbana at a rate equivalent to a turnover of 57% d -1 of the

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... ing stock. Three experiments using natural waters are presented;