Specimens of the marine calanoid copepod Acartia tonsa were exposed for five days under laboratory conditions to the isolated or combined effects of hypoxia and a marine heatwave event to test for their sex-specific life-history and physiological responses to these stressors. Four treatments were used: Control (C: 18 °C, 100 % O₂ sat.), Hypoxia (H: 18 °C, 35 % O₂ sat.), marine heatwave (MHW: 25 °C, 100 % O₂ sat.) and combined conditions (HMHW: 25 °C, 35 % O₂ sat.). This dataset contains fecundity measurement, represented as the number of offspring (eggs, nauplii and copepodites) spawned by females in each experimental condition following the five-day exposure experiment.

The experiment was conducted in the Marine Ecological and Evolutionary Physiology Laboratory (MEEP) at the University of Quebec in Rimouski (UQAR), Rimouski, QC, Canada. Copepods were maintained following the stock culture culturing protocol described in Dam et al. 2021 (https://doi.org/10.1038/s41558-021-01131-5). Namely, approximately 200 copepods were kept in three 5 L aquaria filled with artificial seawater kept at a salinity of 28.4 ± 0.5. The physicochemical parameters of the seawater were the following: temperature of 18 ± 0.4 °C, oxygen saturation of 93.7 ± 6.0 %, pH NBS of 8.20 ± 0.09. The photoperiod was kept at 13h light: 11 h dark. Copepods were fed ad libitum with a mixture of three phytoplankters: Tetraselmis sp., Thalassiosira weissflogii and Rhodomonas salina.----Eggs, offspring and copepodites were retrieved from each aquarium using a 41 µm sieve and placed in a small container. They were then counted one by one under a stereomicroscope (MDF41, Leica) and pipetted in a 500 mL glass beaker.