Methyl halide (CH3X) production from the giant kelp, Macrocystis, and estimates of global CH3X production by kelp1

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Abstract
Production of methyl chloride (CH3Cl), methyl bromide (CH3Br), and methyl iodide (CH3I) was measured from short‐term incubations (light and dark) of Macrocystis pyrifera (kelp) blade tissue and from long‐term culture of Macrocystis blades. Seawater from within a natural Macrocystis bed had elevated CH3X concentrations compared to seawater from outside the kelp bed. Highest concentrations were associated with regions of high biomass density: surface canopy and sporophyll/juvenile frond zone. Rates of methyl halide production (normalized to kelp biomass) were determined from the short‐term incubation, blade culture, and natural population, the latter based on a simple hydrodynamic model. Estimates of global CH3X production based on these production rates and published estimates of global kelp standing stock suggest that kelps (and other marine macroalgae) are not a significant source of global CH3X.