Octopus crawling on land: physiological and biochemical responses of Octopus vulgaris to emersion

Cephalopods are well known for their cognitive capabilities and unique behavioural repertoires. Yet, certain life strategies and behaviours are still not fully understood. For instance, coastal octopuses have been documented (mainly through citizen science and TV documentaries) to occasionally leave the water and crawl in intertidal areas. Yet, there is a complete lack of knowledge on this behaviour's physiological and biochemical basis. Within this context, this study aimed to investigate, for the first time, physiological (routine and maximum metabolic rates and aerobic scope) and biochemical (i.e., antioxidant enzymes activities, heat shock protein and ubiquitin levels, DNA damage, lipid peroxidation) responses of the common octopus, Octopus vulgaris, to emersion. The octopuses' physiological performance was determined by measuring metabolic rates in different emersion treatments and biochemical markers. The size-adjusted maximum metabolic rates (MMRadj) of octopuses exposed to 2:30 min of air exposure followed by re-immersion did not differ significantly from the MMRadj of the chased individuals (control group). Yet, most biochemical markers revealed no significant differences among the different emersion treatments. Our findings showed that O. vulgaris could tolerate exposure to short-term emersion periods due to an efficient antioxidant machinery and cellular repair mechanisms. Alongside, we argue that the use of atmospheric air through the mucus-covered gills and/or cutaneous respiration may also help octopus withstand emersion and crawling on land.