Elevated seawater pCO₂ affects reproduction and embryonic development in the pygmy squid, Idiosepius pygmaeus

The oceans are absorbing additional carbon dioxide (CO₂) from the atmosphere and projected future CO₂ levels and ocean acidification could have negative implications for many marine organisms, especially during early life stages. Cephalopods are ecologically important in marine ecosystems, yet the potential effects of increased partial pressure of CO₂ (pCO₂) in seawater on cephalopod reproduction and embryonic development are little studied. We allowed adult two-toned pygmy squid (Idiosepius pygmaeus) to breed in ambient control (~445 μatm; ~8.05 pH_T) or elevated pCO₂ conditions (~940 μatm; ~7.78 pH_T) and compared reproductive traits in adults and developmental characteristics of their eggs, which remained in control or elevated pCO₂ treatments until hatching. Breeding pairs at elevated pCO₂ produced clutches with 40% fewer eggs, vitelli that were 14% smaller directly after spawning, embryos that were 5% smaller upon hatching, and eggs with an 8% increase in late-stage egg swelling compared with pairs at control conditions. Elevated pCO₂ did not affect fertility, time to hatch, or hatching success. Eggs were laid 40% closer together in elevated pCO₂ compared with control conditions, indicating a possible effect of elevated pCO₂ on reproductive behaviour. These results show that elevated pCO₂ can adversely affect reproduction and embryonic development of the two-toned pygmy squid. As the potential for adaptation is influenced by reproductive success, testing the capacity for squid to adapt to future ocean conditions should be a priority for future research.