| Summary: | Bibliography: pages 85-95. === Procedures for measuring phytoplankton production in the southern Benguela upwelling region were investigated. A 125 ml incubation bottle is recommended for routine primary production measurements. Exposure of production samples to high light intensities during manipulations on deck was found to inhibit rates of production near the bottom of the euphotic zone particularly below a thermocline. Simulated in situ rates of oxygen production were only slightly higher than in situ rates. When ships time is limited, the simulated in situ method can safely be used in local waters. Definite diel periodicity in rates of production at the sea surface was demonstrated and appears to be linked to light levels and nutrient concentrations, as well as to the ratios of light to dark hours. Since diel variation probably decreases with depth, its effect on integrated daily production is reduced. Nevertheless, the time of incubation should be chosen to minimize the effect of periodicity on daily production estimates. The period spanning noon is recommended for local use. Changes in phytoplankton production and biomass are linked with physical and chemical changes in the upwelling system off the Cape Peninsula. Extremely active upwelling was found to limit primary production and from these measurements the annual net primary production in the Cape Peninsula upwelling region is estimated for the first time to be approximately 1.13 kgC.m⁻ ³.y⁻¹.
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