Influence of phytoplankton taxonomic profile on the distribution of total and dissolved dimethylated sulphur (DMSx) species in the North Aegean Sea (Eastern Mediterranean)

Abstract

The distribution of total and dissolved forms of DMSP and total DMSO was surveyed during two sampling cruises conducted in September 2003 and July 2004 in the North Aegean Sea. During the first cruise surface concentrations of DMSPt, DMSPd and DMSOt in the coastal group of stations ranged from 20.92 to 23.71 nM, 15.46 to 15.53 nM and 14.90 to 18.73 nM, respectively, while the offshore group mean concentrations were 27.41 nM (DMSPt) and 14.66 nM (DMSOt). At that time, phytoplankton assemblage was dominated by dinoflagellates. During the second cruise, the surface DMSPt, DMSPd and DMSOt concentrations in the coastal group were not significantly changed compared to the first cruise, while the offshore group presented more elevated values (DMSPt: 33.52 nM; DMSPd: 18.78 nM; DMSOt: 36.49 nM). Interestingly, the vertical distribution and phytoplankton abundance in this cruise were found to have changed, with diatoms being the dominant group in the study area. On both cruises statistically significant correlations between small-sized dinoflagellates (≤ 20 μm) as well as coccolithophores and the concentrations of DMSx compounds were obtained, suggesting the importance of the above phytoplankton groups in the production and distribution of these sulphonic forms. At the same time, no significant correlations were observed between DMSx and diatom species. The strong correlation of DMSx species with the group of dinoflagellates coupled with their decorrelation with Chl-a may serve as indirect evidence of heterotrophic forms dominating dinoflagellate taxa thriving in the area during the stratified period.