Irreversible behavioural impairment of fish starts early: Embryonic exposure to ocean acidification

Highlights: • Fishes raised as eggs under ambient seawater were insensitive to ocean acidification. • Fishes raised as eggs under ocean acidification showed increased anxiety. • This response was not reversed when these fishes were returned to control conditions. • The egg stage may be more sensitive to ocean acidification than the juvenile stage. - Abstract: Long-term species responses to ocean acidification depend on their sensitivity during different life stages. We tested for sensitivity of juvenile fish behaviour to ocean acidification by exposing eggs to control and elevated CO₂ levels, and translocating offspring between treatments in a reciprocal design. After 12 weeks of exposure, activity, inactivity and anxiety levels of juveniles from control eggs were similar, whether juveniles had experienced elevated CO₂ conditions or not, and this pattern was consistent over time. However, juveniles raised as eggs under elevated CO₂ showed increased anxiety levels compared to those from control eggs. This response was not reversed when CO₂-exposed juveniles were translocated to control conditions. Our findings highlight the value of evaluating fish sensitivities to global change pollutants across different life stages, and indicate that sensitivity during the often-overlooked egg stage can be critical with long-lasting impairment of behaviours that are coupled to individual fitness and population persistence.