The primary production by C14, standing crop as ratio of particulate carbon/nitrogen and biossay tests concerning to dissolved nitrogen and phosphorus were investigated in the SW estuahne mangrove area of the Bay of Todos os Santos (Brazil) during 10 months. The phytoplankton displaied in this area a mean density of 9x10(5) cells/liter. The primary productivity showed an average range of 9.52 to 10.93 mgC/m³/h, representing the rate about 45 g C/m³ /year or 181 g C/m² /year. Phytoplankton fraction under 35µ at the stations 0 and 1 was responsible for the most C14 uptake. A negative relationship between primary production and limiting nitrogen and phosphorus was verified. February samples exhibited the most drastic situation regarding to N and P, as limiting factors; an opposite situation corresponded Jo June and July. The relationship between particulated carbon and nitrogen showed a concentration area among the ranges of400/1400 mgC/m³/ and 4/28 mgN/m³, The ratios C/N revealed the most of times a short variation.