Impact of Short- and Long-Term Exposure to Elevated Seawater Pco₂on Metabolic Rate and Hypoxia Tolerance inOctopus rubescens

Abstract

Much of the CO 2 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 longterm impacts of ocean acidification on octopuses. We measured routine metabolic rate (RMR) of Octopus rubescens at elevated CO 2 pressure (PCO 2) with no prior acclimation and 1 or 5 wk of acclimation and critical oxygen pressure (P crit) after 5 wk of acclimation. Our results show that with no prior acclimation, octopuses had significantly higher RMRs in 1,500-matm PCO 2 environments than octopuses in 700-or 360-matm environments. However, after both 1 and 5 wk of acclimation there was no significant difference in RMRs between octopuses at differing PCO 2 , indicating that octopuses acclimated rapidly to elevated PCO 2. In octopuses acclimated for 5 wk at 1,500 matm PCO 2 , we observed impaired hypoxia tolerance, as demonstrated by a significantly higher P crit than those acclimated to 700 matm PCO 2. Our findings suggest that O. rubescens experiences shortterm stress in elevated PCO 2 but is able to acclimate over time. However, while this species may be able to acclimate to nearterm ocean acidification, compounding environmental effects of acidification and hypoxia may present a physiological challenge for this species.

Elevated immune response in Octopus rubescens under ocean acidification and warming conditions

“…Previous work has observed an elevated routine metabolic rate (RMR) in O. rubescens after short-term exposure to elevated pCO 2 , but RMR returned to control levels after 1 week of continuous exposure (Onthank et al 2021), indicating that acute stress responses do not persist for the 3 weeks these trials lasted. This same study, however, also found that hypoxia tolerance was impaired after 5 weeks of exposure, suggesting that subtler chronic stress effects are still present.…”

“…After a minimum 1 week acclimation period (Onthank et al 2021), each octopus was randomly assigned to one of 4 treatment groups: control temperature/control pCO 2 , control temperature/high pCO 2 , high temperature/control pCO 2 , or high temperature/high pCO 2 . The physical arrangement of the tanks within these 4 treatments were interspersed throughout the room to avoid any difference between treatments in light or temperature due to the location of the tanks.…”

“…The Salish Sea, where the octopuses were collected, is a region of temporally and geographically persistently high seawater pCO 2 , with levels commonly exceeding 700 μatm (Murray et al 2015;Onthank et al 2021). The pCO 2 measured at the octopus collection location was 740 µatm and the temperature was 10.1 °C, which in turn were our targeted control conditions.…”

“…Blood was collected 20-22 days after experiments commenced, particularly to perform the immunoassays. Previous research has found that routine metabolic rates of O. rubescens return to normal after a week in a 1500 µatm pCO 2 treatment, suggesting that acute impacts of elevated pCO 2 have largely abated by that time (Onthank et al 2021). A treatment period of approximately 3 weeks was used because it was considered safe to assume that after that period only chronic effects would be measured.…”

“…Though there have been many studies on ocean acidification and sea temperature warming effects on marine organisms, very little work has addressed cephalopods (Parker et al 2013) and to date only one paper has investigated octopuses (Onthank et al 2021). Additionally, there have been no studies addressing these effects on the cephalopod immune response.…”