The marine coccolithophorid phytoplankton species Hymenomonas carterae (class Prymnesiophyceae) produces both dimethylpropiothetin (DMPT) and dimethylsulfide (DMS) in axenic cultures. The rate of DMS production is closely regulated by the cell; it remains independent of environmental sulfate concentration down to levels of 2.5% of the seawater value. Below this sulfate level, DMS production decreases with decreasing sulfate concentration, but significant amounts of DMS are released even under conditions of sulfate-limited growth. Hymenomonas carterae can grow on sulfite, thiosulfate, and cysteine as sulfur sources, but not on methionine. The rate of DMS output is similar for the different sulfur sources.Both the intracellular concentration of DMPT and the rate of output of DMS by H. carterae increase with increasing salinity of the medium. This increase is observed when either salt or sucrose is used to control the osmolarity of the growth medium. Variations in DMPT levels and DMS output were observed within hours after transferring cells to a medium of different osmotic pressure. The intracellular DMPT concentration is of the order of 0.3 mole per liter and contributes significantly to the osmotic pressure in the cell. These results suggest that DMPT plays an important role in osmoregulation by H. carterae.

[1] Results of a single-blind round-robin comparison of satellite primary productivity algorithms are presented. The goal of the round-robin exercise was to determine the accuracy of the algorithms in predicting depth-integrated primary production from information amenable to remote sensing. Twelve algorithms, developed by 10 teams, were evaluated by comparing their ability to estimate depth-integrated daily production (IP, mg C m À2 ) at 89 stations in geographically diverse provinces. Algorithms were furnished information about the surface chlorophyll concentration, temperature, photosynthetic available radiation, latitude, longitude, and day of the year. Algorithm results were then compared with IP estimates derived from 14 C uptake measurements at the same stations. Estimates from the best-performing algorithms were generally within a factor of 2 of the 14 C-derived estimates. Many algorithms had systematic biases that can possibly be eliminated by reparameterizing underlying relationships. The performance of the algorithms and degree of correlation with each other were independent of the algorithms' complexity.

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In the trophic‐dynamic hypothesis, biomass production was assumed limited by factors that control energy transfer. An analysis using trophic‐dynamic models applied to ocean data, however, leads to a rejection of that hypothesis and supports a hypothesis that carnivorous fish production is controlled by the amount of new N annually incorporated into phytoplankton biomass and transferred through food webs. For an average 2.5 trophic transfers from phytoplankton to fish in environments ranging from oceanic to northeast North American coastal waters, N transfer efficiency was a constant 0.28 while C transfer efficiency increased nonlinearly from 0 to an asymptotic value of 0.16. Fish production was more sensitive to variations in phytoplankton production in oligotrophic than in eutrophic marine environments as a result of a nonlinear decrease in f, the ratio of new to total production, as primary production decreased.