Evaluation of the utility of chemotaxonomic pigments as a surrogate for particulate DMSP

High-performance liquid chromatography (HPLC) analysis of accessory pigments, which provides a detailed description of a phytoplankton assemblage over the whole size range, was combined with size fractionation of particulate dimethylsulfoniopropionate (DMSPp) to assess the origin of DMSPp in the sea. More than 200 surface-water samples were collected over contrasting regions of the ocean. Concentrations of DMSPp ranged between 6 and 190 nM. The size fraction < 10 mum accounted for 65 +/- 16% (1 sigma) of DMSPp on average. Concentrations of DMSPp in this size fraction were strongly linearly correlated (r(2) = 0.84, n = 189, P < 0.0001) with the sum of concentrations of Hex-fuco (prymnesiophytes) and But-fuco (chrysophytes-pelagophytes), after excluding 17 samples from the Ligurian Sea (Northwestern Mediterranean Sea) taken during the spring and summer seasons of 1993 and 1994. These samples were unusual because of their high DMSP content. Concentrations of Hex-fuco + But-fuco appear much better surrogates for DMSPp than for DMS. In the size fraction > 10 mum, DMSPp was better correlated with peridinin (dinoflagellates) than fucoxanthin (diatoms) concentrations, but peridinin explained at most 25% of the variability in microplanktonic DMSP: Nearly peridinin-free (<0.01 mg m(-3)) surface waters of the Ligurian Sea during spring and summer contained > 15 nM of DMSPp in the size fraction > 10 mum, i.e., 44 +/- 15% of total DMSPp. Thus, the particulate material exhibited considerably more DMSP than expected from the levels of accessory pigments in the Ligurian Sea during the spring and summer seasons of 1993 and 1994. We suggest that this excess of DMSPp was contributed by heterotrophic nano- and microorganisms.