MEPS 287:11-22 (2005)  -  doi:10.3354/meps287011

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 µg l^-1 for chl a). DMSP_P was correlated with chl a (r² = 0.83) based on regression analysis of log-transformed data. It was even more closely correlated with peridinin (r² = 0.92) and the photoprotective pigment diadinoxanthin (r² = 0.90), indicator pigments for dinoflagellates, a high-DMSP algal group. By contrast, DMSP_P was poorly correlated with zeaxanthin (r² = 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.

KEY WORDS: Dimethylsulfoniopropionate · DMSP · Phytoplankton · Dinoflagellates · Belize · Tropical Lagoon · Barrier Reef · Pigments · CHEMTAX