Dimethylsulfoniopropionate in a salt marsh estuary: correlation to tidal cycle and phytoplankton assemblage composition

Abstract

Salt marsh estuaries emit high levels of dimethylsulfide (DMS), yet little is known about the contribution of tidal creeks, which are rich in phytoplankton that can potentially produce dimethylsulfoniopropionate (DMSP). Quantitative data is presented on the relationship between phytoplankton assemblage structure during tidal cycles in North Inlet, a high-salinity salt marsh estu- ary near Georgetown, South Carolina. While there was little or no correlation between chlorophyll a (chl a) and phytoplankton DMSP (DMSPp) in tidal-creek waters, the DMSPp:chl a ratio showed a strong correlation with tidal stage, being highest at high slack tide and lowest at low slack tide. Phytoplankton assemblage structure determined from HPLC pigment profiles and CHEMTAX ana- lysis (a matrix factorization program to derive taxonomic composition from photopigment ratios) showed that DMSP-rich taxa were highly correlated with the high DMSP:chl a values which occurred at high tide. These were haptophytes, dinoflagellates, cyanobacteria and cryptophytes. Diatoms had a lower correlation coefficient but, because they represented almost 40% of the algal biomass during the tidal cycle, this group could be a significant contributor of DMSPp at high tide. Chlorophytes, prasinophytes, and some chrysophytes showed a strong negative correlation coefficient (r) with the DMSPp:chl a peak. We conclude that the increase in the DMSPp:chl a ratio at high tide is due to an increased contribution of DMSP-rich phytoplankton taxa that enter the creeks from coastal waters during flood tide, and low values resulted from low DMSP-containing resuspended benthic micro- algae, advected from the adjacent salt marsh into the tidal creeks during ebb tide. The data indicate a strong tidal effect on DMSP concentration that is a function of change in phytoplankton assemblage structure.