Effects of iron, silicate, and light on dimethylsulfoniopropionate production in the Australian Subantarctic Zone

Shipboard bottle incubation experiments were performed to investigate the effects of iron, light, and silicate on algal production of particulate dimethylsulfoniopropionate (DMSP p ) in the Subantarctic Zone (SAZ) south of Tasmania during March 1998. Iron enrichment resulted in threefold to ninefold increases in DMSP p concentrations relative to control treatments, following 7 and 8‐day incubation experiments. Additions of Fe and Si preferentially stimulated the growth of lightly‐silicified pennate diatoms and siliceous haptophytes, respectively, to which we attribute the increased DMSP p production in the incubation bottles. Both of these algal groups were previously believed to be low DMSP p producers; however, our experimental data suggest that addition of iron and silicate to the low‐silicate low‐iron waters of the SAZ will result in increased production of DMSP p by lightly silicified diatoms and siliceous haptophytes, respectively. Increased irradiance enhanced DMSP p production in iron‐amended treatments with both low (0.5 nM) and high (5 nM) concentrations of added iron. However, the role of light in stimulating DMSP p production was apparently of secondary importance compared to the effects of iron addition. The combination of high irradiance and high iron enrichment produced the highest DMSP p production in the experiments, suggesting that iron and light may have a synergistic effect in limiting algal DMSP p production in subantarctic waters.