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Röckner, J. L., Lopes, V. M., Paula, J. R., Pegado, M. R., Seco, M. C., Diniz, M., Repolho, T., & Rosa, R. (2024). Octopus crawling on land: physiological and biochemical responses of Octopus vulgaris to emersion. Marine Biology, 171(1), 14. https://doi.org/10.1007/s00227-023-04333-x
Common Octopus (Octopus vulgaris). Image Credits: Kevin Bryant via Flickr Creative Commons
If you’ve read Remarkably Bright Creatures by Shelby Van Pelt, you know that the octopus is, as the title indicates, a highly intelligent marine animal that is capable of surviving and functioning outside of water for long periods of time. A study performed in Portugal indicates that this unbelievable quality of octopuses is due to their many physiological adaptations–and that Van Pelt’s novel, despite being fiction, is scientifically plausible.
While this quality has been observed for hundreds of years, researchers finally set out to understand how such a phenomenon occurs. What biological features allow for the common octopus, Octopus vulgaris, to do what seems impossible?
Remarkably Shallow Habitats
Tidepool. Image Credits: Mookie Forcella via Flickr Creative Commons
Tidepools, unique habitats found in shallow-water tidal areas, only make suitable homes for species that can survive in frequently changing environments. These species need to be able to adapt to varying temperatures, salinity, and even air exposure. Typically, these conditions bring to mind starfish and mussels, but it is evident that larger, faster moving species like octopuses are also capable of surviving in tidepools.
Species that repeatedly transition from breathing water to breathing air are equipped with a mechanism that reduces production of reactive oxygen species (ROS), produced when converting food into energy using oxygen. When overproduced, ROS can damage healthy cells.
While it is unclear if octopuses possess this mechanism, they are known to forage in tidepools and escape aquarium tanks. Previous research shows that octopuses can slow their heart rate and improve their anaerobic (without oxygen) metabolism when oxygen is scarce. However, this study aimed to discover how similar octopus responses are to other intertidal species by simulating low-oxygen conditions and observing how octopuses respond to it.
Remarkably Detailed Methods
Researchers collected 20 common octopus specimens and placed them each in identical tanks. Light conditions were maintained for 12 hours, followed by 12 hours of darkness.
After being placed into the tanks, the octopuses were divided into five groups, each treated differently to test different air exposure scenarios:
- “Emersion” (treatment): seawater was let out of the tank without letting the octopus escape. The octopus was then exposed to the air for 2:30 minutes.
- “5 min recov” (treatment): “Emersion” treatment performed, and then the tank was filled with water again, followed by a 5 minute recovery period.
- “24 h recov” (treatment): similar to “5 min recov”, but followed by a 24 hour recovery period.
- “Chase control” (control): following 24 hour monitoring of standard metabolic rates (SMR), the octopus was put into a new tank and chased by human hands for five minutes, then it was moved to a new tank, where its oxygen consumption was monitored for 24 hours.
- “Immersion” (control): the octopuses’ SMR was monitored for 24 hours.
Researchers collected oxygen consumption rates (OCR) to measure aerobic metabolism.
Remarkably Surprising Results
The “5 min recov” group showed similar maximum metabolic rates to the “chase control” group, indicating that air exposure was a stressor for the octopuses of similar intensity to being chased by a predator. Both conditions led to increased oxygen consumption, but in the “5 min recov” group, the octopus was able to quickly return to normal oxygen consumption, similar to a human breathing heavily for a brief time after running a race.
Unlike other intertidal animals, the octopuses in this study did not increase antioxidant activity in response to oxygen stress. Interestingly, this suggests that the 2:30 mins out of water was not a long enough time that the octopuses would need to change their metabolic process; they are therefore capable of being out of the water for a lot longer than that before needing to compensate.
A Remarkably Relevant Study
The results of this study revealed that octopuses use a long list of unique physiological adaptations to anaerobic conditions.
For one, they can produce glucose without using oxygen. They can also redirect their blood flow to more essential organs to conserve oxygen and reduce protein synthesis in anticipation of anaerobic conditions, as shown in the “5 min recov” group.
Two minutes and 30 seconds was not enough time to cause significant stress to the octopuses. It is likely, then, that an octopus that forages in tidepools, walks on land, or escapes his aquarium tank to befriend the friendly old woman (as in Remarkably Bright Creatures) is actually doing it a lot more often, and for a lot longer, than humans know.
This fascinating study has both positive and negative implications for humans. First, with octopuses having this ability to adapt, their chances of survival as ocean conditions evolve due to climate change is high. However, with octopuses coming onto land more, humans need to be more vigilant about how their actions might impact marine life–not only should we continue to prevent ocean pollution, we should also be extra careful about impacting the coasts. You never know who might come crawling out of the ocean to explore.
I am an MPS student at the University of Miami’s Rosenstiel School of Marine, Atmospheric, and Earth Sciences pursuing a degree in Marine Biology and Ecology on the Tropical Marine Ecosystem Management Track. After graduating, I plan to use my education and experience to pursue a career in science writing or film production to help communicate the importance of the ocean to the general public.
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