Dimethylsulfoniopropionate (DMSP) and its relation to algal pigments in diverse waters of the Belize coastal lagoon and barrier reef system

Abstract

Dimethylsulfoniopropionate (DMSP) and algal pigments were measured in waters from a variety of sites in the Belize coastal lagoon and adjacent barrier reef system. Particulate concentrations of DMSP (DMSP P ) and chl a varied by 2 orders of magnitude (1.1 to 130 nmol l -1 for DMSP and 0.040 to 2.9 g l -1 for chl a). DMSP P was correlated with chl a (r 2 = 0.83) based on regression analysis of log-transformed data. It was even more closely correlated with peridinin (r 2 = 0.92) and the photoprotective pigment diadinoxanthin (r 2 = 0.90), indicator pigments for dinoflagellates, a high-DMSP algal group. By contrast, DMSP P was poorly correlated with zeaxanthin (r 2 = 0.13), a marker for cyanobacteria which are thought to contain little or no DMSP. The highest DMSP P and chl a concentrations and highest mean DMSP P :chl a molar ratio (39 12) were observed in a eutrophic mangrove embayment, whose phytoplankton community was dominated by dinoflagellates. Much lower chl a and DMSP P values and a somewhat lower average DMSP P :chl a molar ratio (29 14) were observed at sites in the vicinity of the outer barrier reef/island system, where an estimated 64% of the chl a on average occurred in cyanobacteria. In a diel study at one of these sites, the DMSP P /chl a ratio increased during the day and decreased at night, a pattern that did not appear to be caused by variations in the algal community. The diel pattern instead may reflect a daytime increase in cellular DMSP concentration. Given DMSP's putative antioxidant function, the increase in DMSP P :chl a ratios may represent a physiological response to help protect algal cells from increased oxidative stress during the day linked to solar UV-radiation and photosynthesis.