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Production, in terms of volume of particulate matter, was studied in four developing phytoplankton communities in newly upwelled waters of the southern Benguela Current. Growth (max doublings d-' -2.9, max C production -21 g m-2 d-l) of phytoplankton upwellcd from source water was rapid, with little evidence of a lag phase. The growth pattern differed for each community encountered and was related to the rate of mixing of the water column and the nutrient and light regimes. Production rates were highest in newly upwelled waters and lowest under limiting light and during periods of nitrate depletion in the upper mixed layer. Changes in growth rates were also attributed to short-term wind variations that caused water bodies to mix and change the nutrient regimes.Growth occurred over a wide size range of particles, mostly in the range 20-80-pm equivalent spherical diameters (ESD), corresponding to chains of diatoms, but occasionally also in the range of 6-l 4-pm ESD, suggesting some growth of small-celled algae and microflagellates. A diel variation was observed, with volume increases during the day greatly exceeding those at night except under extreme limiting conditions when thcrc was some growth in the dark.

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