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.

Dens are a crucial component of the life history of most shallow water octopuses. However, den usage dynamics have only been explored in a few species over relatively short durations, and Octopus rubescens denning behavior has never been explored in situ. We built four underwater camera traps to observe the behavior of Octopus rubescens in and around their dens. To distinguish individuals, octopuses were captured and given a unique identifiable visible implant elastomer tag on the dorsal side of their mantle. After being tagged and photographed, each octopus was released back to its original capture site within its original den bottle. The site is unique in that octopuses reside almost exclusively in discarded bottles, therefore aiding in locating and monitoring dens. Motion-activated cameras were suspended in a metal field of view above bottle dens of released octopuses to observe den associated behaviors. Cameras were regularly retrieved and replaced to allow continuous monitoring of den locations in 71-hour intervals for over a month. We found that O. rubescens was primarily active during the day and had frequent interactions with conspecifics (other members within the species). We also found that rockfish and red rock crabs tended to frequent den locations more often when octopuses were not present, while kelp greenling both visited dens more frequently and stayed longer when octopuses were present. Our results demonstrate the utility of motion-activated camera traps for behavioral and ecological studies of nearshore mobile organisms.

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To study the effects of ocean warming and acidification on the immune response of octopuses, 24 Octopus rubescens were collected from Driftwood Park, Washington (48°09′48.9"N 122°38′14.1"W) April-July 2018. Following 3 weeks in elevated pCO 2 , elevated temperature, or the combination thereof, immunological parameters were measured including total hemocyte count, phagocytosis activity, superoxide production, and lysozyme activity. Increased pCO 2 elicited an increase in the number of circulating hemocytes, which are responsible for the cellular immune response, indicating a stress response. As a result, total phagocytosis also increased. This is the first study examining the effects of climate change on the immune system of cephalopods.

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