We investigated the reproductive biology of the planktonic harpacticoid copepod Euterpina acutifrons, including morphometric data, egg production rates (EPR) and viability, and weight-specific egg production. Experiments were carried out during 1 year in an inner-shelf area off Ubatuba (SE Brazil), a site seasonally influenced by bottom intrusions of the relatively cold and nutrient-rich South Atlantic Central Water (SACW). We hypothesized that E. acutifrons attain higher reproductive rates when SACW penetrates in this region. Live females were incubated individually in cell culture plates during two periods of 24 h each, under controlled temperature and light conditions. Euterpina acutifrons carried on average 16.9 AE 6.9 eggsÁsac À1 , ranging between 10.8 AE 5.7 and 30.8 AE 7.4 eggsÁsac À1 . Estimated EPRs ranged from 6.3 AE 3.4 to 13.6 AE 4.2 eggsÁfemale À1 Áday À1 , with mean weight-specific egg production rates of 0.06 AE 0.04 and 0.17 AE 0.08 per day. Euterpina acutifrons was not directly influenced by SACW intrusions, but body length and clutch size were positively related to temperature and chlorophyll content. Egg hatching time was clearly dependent on water temperature, as a 2°C increase resulted in a decrease of 15 h in egg hatching time. This shows that even a small variation in temperature may considerably affect E. acutifrons population dynamics. Reproductive traits of this pelagic harpacticoid seem, therefore, to be controlled by the trade-offs between increased food supply and the metabolic demands at low temperatures associated with SACW bottom intrusions toward this coastal area.