Oscillatoria was found in the surface waters of the South Atlantic Bight during each of four seasonal cruises. There were large concentrations nearshore in September, December, and April while a shelf wide bloom with filament numbers as high as 36,000 1-1 prevailed
in July. Oscillatoria appears to be endemic to the shelf, is not necessarily contributed by the Gulf Stream nor are the blooms related to the subsurface Gulf Stream intrusions. In July water column stability, high temperature and nutrient deficiency seemed to favor Oscillatoria
but it is not clear why nearshore blooms occurred in September and December when unstable conditions, cooler water and relatively high nutrient loads existed. While we calculate that nitrogen fixation by Oscillatoria is not as important as the contribution of total nitrogen added from
coastal and intrusion sources, the biomass and productivity represented by Oscillatoria must significantly influence secondary production on the shelf.
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