Laboratory production of bromoform, methylene bromide, and methyl iodide by macroalgae and distribution in nearshore southern California waters

Production rates of bromoform (CHBr,), methylene bromide (CH,Br,), and methyl iodide (CH31) were measured in the laboratory for 11 species of marine macroalgae. Production rates of the volatile bromomethanes extrapolated to a global scale suggest that marine macroalgae produce 2 x 10” g Br yr-I (1 x lo9 mol Br yr I), 98% of which is bromoform. Laminarians (kelps) produce 61% of this organic Br. These calculations suggest that marine macroalgae are important in the biogeochemical cycling of Br. Seawater concentrations of CHBr,, CH,Br,, and CH,I were determined from various southern California coastal locales. High concentrations were measured in seawater from the canopy and the bottom of a dense bed of Macrocystis as compared to other sites. Surface seawater concentrations of these halomethanes showed a strong cross-shore gradient with the highest concentration in the kelp canopy and the lowest at 5 km offshore. Seawater adjacent to decaying macroalgae on the bottom of a submarine canyon was not enriched in halomethanes relative tosurface water. Water exiting a productive estuary was enriched only with CH,Br,, although two algal species that are abundant there (U/vu and Enteromorpha) showed high laboratory production rates ofboth CHBr, and CH,Br,. Bromoform (CHBr,), methylene bromide (CH,Br,), and methyl iodide (CH,I) are major natural vectors of gaseous bromine (Penkett et al. 1985) and iodine (Rasmussen et al. 1982) to the atmosphere. Productive coastal waters are enriched with CHBr, (Fogelqvist and Krysell 199 1; Class and Ballschmiter 1988), CH,Br, (Class and Ballschmiter 1988), and CHJ (Lovelock 1975; Manley and Dastoor 1988) due in part to their production by marine macroalgae and possibly by marine microbes. Seaweeds appear to be the dominant natural oceanic source of CHBr, and CH2Br2 (Gschwend et al. 1985). In addition to field observations, macroalgal production of these halomethanes has been measured in the laboratory. Gschwend et al. (1985) reported production rates for I Corresponding author. Acknowledgments We thank M. N. Dastoor for use of the EC-GC and J. Delacuesta for assistance. This work was supported by CSULB, NSF, and WESTGEC (DOE). CHBr, [0.14-14 pg d-l (g DW)-I; g DW = g dry wt] and CH,Br, [0.25-21 pg d-l (g DW)-I] for six algal species. Previous work (Manley and Dastoor 1988) on production rates of CH31 [ 100-300 ng d-l (g DW)-l] was performed on five kelp species (order Laminariales). Several lines of evidence support the conclusion that algae, not associated microbes, are primarily responsible for the halomethane production observed (Gschwend et al. 1985). Furthermore, axenic tissue cultures of Macrocystis pyrifera have produced CH31 (Manley and Dastoor 1988). The biosynthesis of halomethanes by marine macroalgae has been studied by several researchers (e.g. Theiler et al. 1978; Wuosmaa and Hager 1990; Wever et al. 199 1). Enzymes involved in methyl halide (monohalomethane) production appear to be different from those involved in polyhalomethane production. This study determined production rates of CHBr,, CH,Br,, and CH,I by estuarine and nonestuarine subtidal macroalgae. The focus was on ecologically abundant and pre-