During March, 1963, primary production and standing stock of phytoplankton were measured at six stations in a limited area of the equatorial Atlantic. A progressive decrease in production (as measured by C14 uptake) and in numbers of organisms per liter was found from the
coastal area to the oceanic region. Values for primary production ranged from 0.864 to 0.014 g C/m2/day from the more coastal station (No. 1) to the oceanic one (No. 6). Maximum standing stock was found at the surface at station 1 (523,180 cells/liter), and the minimum at
15 m depth, at station 6 (8,700 cells/liter). The phytoplankton appeared to be concentrated in the upper layers of the euphotic zone at the coastal station (No. 1). A gradual change in the relative abundance of the different groups was found. At the stations near to the coast, neritic
diatoms constituted the bulk of the phytoplankton, whereas at the oceanic stations, coccolithophores and oceanic forms of diatoms were more abundant.
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