This dataset reports the results of an experiment on the impacts of ocean warming and food ration on the fecundity of the sea star Asterias rubens. Males and females were acclimated for 26 weeks (from October 2nd 2023 to April 1st 2024 included) either to +0°C or +3°C compared to the usual seasonal temperature, and either to 1 or 3 mussels per sea star twice a week, in a controlled laboratory environment. Biometric parameters (body weight, arm length, pyloric caeca weight, gonad weight, pyloric index, gonadosomatic index), gametes concentration (number of gametes per gram of gonad) and fecundity (number of gametes per individual) were assessed at the end of the acclimation period. Data included are: 1) Calendar: information on the photoperiod and the temperature applied at each experimental week. 2) Live_Mussels: numbers of uneaten mussels from the previous feeding session. 3) Biometric_Parameters: biometric parameters (body weight, arm length, pyloric caeca weight, gonad weight, pyloric index, gonadosomatic index) measured for each sea star at the end of the experiment. 4) Female_Fecundity: Gamete concentration and individual fecundity of females at the end of the experiment. 5) Male_Fecundity: Gamete concentration and individual fecundity of males at the end of the experiment.