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

High-performance liquid chromatography (HPLC) analysis of accessory pigment s, 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 regio ns of the ocean. Concentrations of DMSPp ranged between 6 and 190 nM. The s ize fraction < 10 mum accounted for 65 +/- 16% (1 sigma) of DMSPp on averag e. Concentrations of DMSPp in this size fraction were strongly linearly cor related (r(2) = 0.84, n = 189, P < 0.0001) with the sum of concentrations o f Hex-fuco (prymnesiophytes) and But-fuco (chrysophytes-pelagophytes), afte r excluding 17 samples from the Ligurian Sea (Northwestern Mediterranean Se a) taken during the spring and summer seasons of 1993 and 1994. These sampl es were unusual because of their high DMSP content. Concentrations of Hex-f uco + But-fuco appear much better surrogates for DMSPp than for DMS. In the size fraction > 10 mum, DMSPp was better correlated with peridinin (dinofl agellates) than fucoxanthin (diatoms) concentrations, but peridinin explain ed 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 considerab ly more DMSP than expected from the levels of accessory pigments in the Lig urian Sea during the spring and summer seasons of 1993 and 1994. We suggest that this excess of DMSPp was contributed by heterotrophic nano- and micro organisms.