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 to-surface 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,.

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Macrocystis pyrifera (Giant Kelp), a dominant macroalgal species in southern California, produced I71 ng per g fresh wt (gfwt) per day of CHBr, and 48 ng gfwt-' d-' of CH,Br, during laboratory incubations of whole blades. Comparable rates were measured during in situ incubations 01 intact fronds. Release of CHBr, and CH,Br, by M. pyr$eru was affected by light and algal photosynthetic activity, suggesting that environmental factors influencing kelp physiology can affect halomethane release to the atmosphere. Data from H,O, additions suggest that brominated methane production during darkness is limited by bromide oxidant supply. A bromine budget constructed for a region of southern California indicated that bromine emitted from the use of CH,Br as a fumigant (1 X 1 Ox g BI yr -I) dominates macroalgal sources (3 X 10" g Br yr-I). Global projections, however, suggest that combined emissions of marine algae (including microalgac) contribute substantial amounts of bromine to the global cycle, perhaps on the same order of magnitude as anthropogenic sources.

The effect of nitrogen supply on nitrogen content and growth rate of juvenile Macrocystis pyrifera (L.) C. A. Agardh sporophytes was studied in two types of experiments: growth in continuously flowing mixtures of deep (nutrient‐rich) and surface (nutrient‐poor) seawater, and growth in batch cultures with alternate 7–10 day periods in deep and surface water. In the continuous flow experiments, the nitrogen content of the plants increased with the increased concentration of nitrate in the seawater. In the batch culture experiments, a lag period of 3–7 days often occurred before changes in the nitrogen supply were reflected in corresponding changes in the nitrogen content of the plants. Growth rates were a linear function of tissue nitrogen which varied between 1–3% dry weight. Saturation of growth rate as a function of tissue nitrogen did not occur, although tissue nitrogen levels did saturate as a function of external nitrate supply. Juvenile M. pyrifera sporophytes do not appear to “store” nitrogen. Total nitrogen varies from 1–6% dry weight in Laminariales and Fucales, but only some species of Laminaria appear to accumulate large pools of “surplus” nitrogen.

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