Impact of short- and long-term exposure to elevated seawater pCO2 on metabolic rate and hypoxia tolerance in Octopus rubescens

Much of the CO₂ released by human activity into the atmosphere is dissolving into the oceans making them more acidic. In this study we provide the first data on the short- and long-term impacts of ocean acidification on octopuses. We measured routine metabolic rate (RMR) and critical oxygen pressure (P_crit) of Octopus rubescens at elevated CO₂ pressure (pCO₂) with no prior acclimation, one, and five weeks acclimation. Octopuses showed significantly higher RMRs in 1500 μatm pCO₂ environments with no prior acclimation than octopuses in 700 μatm or 360 μatm environments. However, both one and five weeks of acclimation showed no significant difference in RMRs between octopuses at differing pCO₂, indicating that octopuses acclimated rapidly to elevated pCO₂. In octopuses acclimated for five weeks at 1500 μatm pCO₂ we observed impaired hypoxia tolerance as demonstrated by a significantly higher critical oxygen pressure than those acclimated to 700 μatm pCO₂. Our findings suggest that O. rubescens experiences short-term stress in elevated pCO₂, but is able to acclimate over time. However, while this species may be able to acclimate to near-term ocean acidification, compounding environmental effects of acidification and hypoxia may present a physiological challenge for this species.