Methyl iodide production from marine phytoplankton cultures

Unialgal cultures of 15 species of marine phytoplankton were examined for the production of methyl iodide (CH3I). CH3I production was quantified during log and stationary phases of phytoplankton growth in f/2 medium and compared to CH3I levels in control vessels. Significant increases in CH3I production were seen in five cultures. Phytoplankton CH3I production varied from a low of 10(-4) amol CH3I cell(-1) d(-1) to a high of 8 x 10(-1) amol CH3I cell(-1) d(-1). In three diatom cultures, the increase in total CH3I and cell-based CH3I production rates were much higher during the log phase than during the stationary phase, even though the bacterial numbers continued to increase. supporting the premise of phytoplankton CH3I production. In two cultures, it was more difficult to distinguish between phytoplankton and bacterial production. Additional biotic and abiotic sources and sinks of CH3I were considered in the analysis, including bacterial consumption, chemical removal and photochemical production. The only significant CH3I sink during the course of the experiment was its nucleophilic substitution with Cl-.