Parental exposure to elevated pCO2 influences the reproductive success of copepods

Substantial variations are reported for egg production and hatching rates of copepods exposed to elevated carbon dioxide concentrations (pCO 2 ). One possible explanation, as found in other marine taxa, is that prior parental exposure to elevated pCO 2 (and/or decreased pH) affects reproductive performance. Previous studies have adopted two distinct approaches, either (1) expose male and female copepoda to the test pCO 2 /pH scenarios, or (2) solely expose egg-laying females to the tests. Although the former approach is more realistic, the majority of studies have used the latter approach. Here, we investigated the variation in egg production and hatching success of Acartia tonsa between these two experimental designs, across five different pCO 2 concentrations (385-6000 µatm pCO 2 ). In addition, to determine the effect of pCO 2 on the hatching success with no prior parental exposure, eggs produced and fertilized under ambient conditions were also exposed to these pCO 2 scenarios. Significant variations were found between experimental designs, with approach (1) resulting in higher impacts; here >20% difference was seen in hatching success between experiments at 1000 µatm pCO 2 scenarios (2100 year scenario), and >85% at 6000 µatm pCO 2 . This study highlights the potential to misrepresent the reproductive response of a species to elevated pCO 2 dependent on parental exposure.