The relation between distribution of living planktonic Foraminifera species and selected elements of the equatorial Atlantic current system has been investigated through the use of depth-controlled, opening-closing net, quasi-synoptic plankton samples, as well as hydro-casts, S-T-D lowerings, and direct current measurements. Physico-chemical data collected with the biologic samples were used to define major biotopes within the current system. They showed salinity variation to be one of the most important factors affecting foraminiferal distribution and temperature variation to be of lesser importance; variations in salinity as small as 0.5 ppt. appear to exert strong influence on population variation within the planktonic Foraminifera. Because of such sensitivity, plankto ic Foraminifera may be very useful as water-mass indicators in studies of oceanic-current and circulation patterns.

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