A NITRATE-DEPENDENT SYNECHOCOCCUS BLOOM IN SURFACE SARGASSO SEA-WATER
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Considerable debate exists concerning the magnitude of oceanic primary production, its rate of transfer to other trophic levels and turnover times of carbon and nitrogen1-5. In nitrogen-limited ocean systems, episodic increases in nitrate concentrations can support a significant fraction of annual phytoplankton production5. Yet little information is available regarding the distribution of nitrate in seasonally stratified oceanic surface waters, because concentrations are below the 0.03 M detection limit of colorimetric methods6. We present the first evidence that high surface productivity in stratified Sargasso Sea water was supported by nanomolar changes in nitrate concentrations. This change was stoichiometrically consistent with the subsequent cellular production of a cyanobacterial (Synechococcus) bloom. Initially, cellular phycoerythrin and chlorophyll pigments increased, after which growth was enhanced to near maximum rates, and grazing was closely coupled to production. These observations suggest that Synechococcus occupies an important trophic position in the transfer of new nitrogen into the oceanic food web. 1988 Nature Publishing Group.
