Biological control of short-term variations in the concentration of DMSP and DMS during a Phaeocystis spring bloom

In the spring of 1995. short-term variations in the concentration of partic ulate and dissolved dimethylsulfoniopropionate (DMSP) and dimethylsulfide ( DMS) were monitored in the western Wadden Sea, a shallow coastal region in open connection with the North Sea. Significant correlations were found bet ween abundance of Phaeocystis globosa and particulate DMSP; concentrations increased rapidly from 100 to 1650 nM in the middle of April. Highest DMS c oncentrations were found during the initial phase of the exponential growth of the bloom. DMS production and loss rates of DMSP and DMS were estimated experimentally during various phases of the bloom. DMS production and cons umption were roughly in balance, with production only slightly exceeding co nsumption at the start of the bloom. Rates of production and consumption we re highest during the exponential growth phase of Phaeocystis and declined in the course of the bloom (from 300-375 to less than 5 nmol dm(-3) d(-1)). Demethylation of DMSP increased during the bloom (from 11 to 1300 nmol dm( -3) d(-1)); it accounted for up to 100% of the DMSP loss at the end of the bloom. The shift from DMSP cleavage to demethylation in the course of a Pha eocystis bloom implies that DMS concentrations are not necessarily highest at the peak or towards the end of blooms. (C) 1998 Elsevier Science B.V. Al l rights reserved.