Effect of tidal flux, salinity and phytoplankton assemblage composition on particulate dimethylsulfoniopropionate (DMSPp) in salt marsh tidal creeks

Dimethylsulfoniopropionate (DMSP), a precursor to dimethylsulfide (DMS) gas (thought to play a role in climatic regulation), is abundant in marine environment and is produced by certain species of marine phytoplankton. Knowledge of the factors affecting DMSP production in the marine phytoplankton is important in estimating global DMS budgets. This research was aimed at understanding the effect of salinity and nutrient gradients, water temperature, tidal flux and phytoplankton assemblage composition on variations in estuarine phytoplankton DMSP production. In the tidal creeks of the North Inlet estuary system, the DMSPp:Chl a ratio was directly correlated with the tidal stage. The ratio, which normalizes the DMSP level to the amount of phytoplankton biomass present, is highest at high tide and lowest at low tide. This variation was attributed to the tidal flux of phytoplankton species in the tidal creek waters. Dinoflagellates, haptophytes and diatoms appear to be of primary importance in this tidal exchange of DMSP. When the variation in ratio was assessed on a temporal basis, it was observed to peak in the months with cooler water temperatures in late fall or winter; the time at which the peak appeared seems to be related to the amount of rainfall in the preceding months. Prasinophyte A and dinoflagellate species appear to be important contributors of DMSP when these ratios peaked. The variation in the DMSPp:Chl a ratio was always strongly correlated to water salinity along the gradients. It was observed that the peak in the ratio during the cooler months mentioned above was evident only in water with salinities above 30 ppt. These data suggested that higher values of DMSPp:Chl a found at higher salinities were attributed to higher levels of dinoflagelletes, haptophytes (with 19 ' Hex) and Prasinophytes (lacking prasinoxanthin). Salinity range between 30 and 35 ppt was thought to be crucial for controlling the DMSP levels in the water. DMS producing bacteria were also found in higher numbers both at low tide water and in intertidal sediments of a tidal creek than in high tide waters. They were also reported at sites far inland, never exposed to DMSP.