) throughout the study area. Causal links established with path analysis indicate that this potential seemed to be controlled by water temperature and chlorophyll a concentrations. 202: 27-40, 2000 of sulfur (Lovelock et al. 1972, Andreae 1990, Bates et al. 1992.
KEY WORDS: Dimethylsulfide (DMS) · Dimethylsulfoniopropionate (DMSP) · Production rates · Low temperature · Bacteria · Substrate utilization
Resale or republication not permitted without written consent of the publisherMar Ecol Prog SerThe main precursor of DMS is dimethylsulfoniopropionate (DMSP, [CH 3 ] 2 S + CH 2 CH 2 COO -), an osmolyte produced by certain groups of macro-and microalgae, similar in structure to the betaines (Vairavamurthy et al. 1985, Blunden & Gordon 1986, see Kirst 1996and Malin & Kirst 1997 for a review). Among phytoplankton, dinoflagellates and prymnesiophytes are known to possess high intracellular DMSP (Keller et al. 1989). Release of DMSP into the water during the exponential growth phase of the algae, i.e. exudation, is considered to be small (Laroche et al. 1999). The formation of an important pool of dissolved DMSP (DMSP d ) in marine surface waters is associated with cell senescence at the end of a bloom (Turner et al. 1988, Matrai & Keller 1993 especially since autolysis of phytoplankton seems to be an important process in the natural environment (Van Boekel et al. 1992, Brussaard et al. 1995. Liberation of DMSP d can furthermore be concomitant with DMS production via cell lysis due to zooplankton grazing (Dacey & Wakeham 1986, Leck et al. 1990) and viral infections (Malin et al. 1994, Bratbak et al. 1995, Hill et al. 1998. In open ocean regions, DMSP d concentrations as high as 200 nmol l -1 have been observed (Malin et al. 1993). In the water column, DMSP d is subject to rapid turnover. A part of the DMSP d undergoes enzymatic cleavage forming DMS and acrylic acid in equimolar amounts (Challenger & Simpson 1948, Cantoni & Anderson 1956). Activity of the enzymes (DMSPlyases) catalyzing the cleavage of DMSP has been observed and characterized in certain algae, for example Phaeocystis sp. or Emiliania huxleyi (Stefels & van Boekel 1993, Stefels & Dijkhuizen 1996, Steinke et al. 1998, and in bacteria from various aquatic environments (de Souza & Yoch 1995a, Taylor & Visscher 1996 and references therein). Bacterial cleavage of DMSP d to DMS and acrylic acid seems to be motivated by the use of the latter as a carbon source (Dacey & Blough 1987, Ledyard 1993. By incubating whole surface water communities with additions of DMSP d , it has been shown that enzymatic conversion of DMSP d to DMS is concentration and temperature dependent (Kiene & Service 1991), and follows Michaelis Menten type kinetics (Ledyard 1993). In natural waters, the kinetic parameters K m and V max of DMSP d consumption and DMS production show as yet unexplained variability that could be due to differences in microbial communities on seasonal or spatial scales (Ledyard 1993, Ledyard & Dacey 1996a.Bacterial demethylation of DMSP d to 3-methylmercaptopr...