Seasonal variation in dimethylsulfoniopropionate related to microphytobenthos composition in intertidal estuarine sediments

Dimethylsulfoniopropionate (DMSP) and algal pigments were measured monthly over 1 yr (May 1997 to June 1998) in intertidal sediments at 2 sampling sites along the Wester- and Oosterschelde (Netherlands). Temperature, salinity and dissolved inorganic nitrogen (DIN) were measured in the pore water and qualitative microscopic observations were made on the microphytobenthos present in the sediment. Both DMSP and pigment content correlated positively with temperature and salinity. However, the chlorophylla- or fucoxanthin-specific DMSP contents were not affected by temperature, salinity or DIN. Simultaneous peaks of DMSP and chlorophyllaand fucoxanthin were observed in spring and in summer, and at 1 station also in winter. These peaks coincided with increases in epipelic diatoms. The DMSP content correlated with chlorophyllaand fucoxanthin and this relationship improved by excluding samples with a low ratio of fucoxanthin to chlorophylla(chla) indicative of a low amount of diatoms relative to other microalgae. The sediment molar ratio of DMSP:chlawas 9.2 ± 5.6 and 5.1 ± 3.6 for the Wester- and Oosterschelde, respectively, values similar to the cellular ratio in cultured diatoms. These results suggest that diatoms were the most important source of DMSP in the sediment. In summer, cyanobacteria and green algae were also present. While cyanobacteria did not contribute to the DMSP content, the data suggest that the amount of DMSP produced by other algae (probably Euglenophytes) produced similar to that produced by diatoms. Hence, microphytobenthos biomass and community composition were the main factors determining the DMSP content in the intertidal sediments of the Schelde estuary.