This is a study on the effects parental exposure of elevated CO₂ on the reproduction and embryonic development of the two-toned pygmy squid (Idiosepius pygmaeus). Adult squid were exposed to either control or elevated CO₂ conditions for 14 days prior to being paired together to breed. After eggs were spawned, they were counted and photographed under microscope. The development of the embryos was then recorded with photographs (every 24 hours) until all embryos had hatched. From the photographs and count data, variables of development and reproduction were collected including number of eggs per clutch, percent of eggs that were fertile, percent of embryos that were deformed, number of embryos to hatch, time it took them to hatch from spawning, as well as size of the egg cases and embryos during distinct stages of embryonic development. These variables were compared to determine if there was an effect of elevated CO_2.

Abstract [Related Publication]: The oceans continue to absorb atmospheric carbon dioxide (CO₂) and projected future CO₂ levels 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 elevated CO₂ 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) or elevated CO₂ conditions (~940 µatm) and compared reproductive traits in adults and developmental characteristics of their eggs between treatments. Breeding pairs at elevated CO₂ produced clutches with 40% fewer eggs, embryos that were 14% smaller directly after spawning and 5% smaller upon hatching, and an 8% increase in late-stage egg swelling compared with pairs at control conditions. Elevated CO₂ did not affect fertility, time to hatch, or hatching success. Eggs were laid 40% closer together in elevated CO₂ compared with control conditions, indicating a possible effect of elevated CO₂ on reproductive behaviour. These results show that elevated CO₂ 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.