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7 Animals That Can Survive Without Oxygen

Gaztelugache, Bermeo, País Vasco, España
Diego Delso, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

When we think of life on Earth, one of the essential elements that comes to mind is oxygen. It’s the air we breathe, the element that powers our cells, and the foundation for the life energy most creatures rely on. However, in the vast tapestry of nature, some organisms have evolved remarkable adaptations to survive without oxygen. These anaerobic animals inhabit some of the most inhospitable environments on the planet, showcasing the incredible diversity of evolutionary survival strategies. Let’s explore seven fascinating animals that have learned to live in oxygen-free (or nearly oxygen-free) environments.

1. Loriciferans The Deep Sea Mysteries

Pulpo común (Octopus vulgaris), Parque natural de la Arrábida, Portugal,
Diego Delso, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

Loriciferans are microscopic organisms that reside in the extreme depths of the ocean. Not discovered until the 1980s, they are remarkable for their capability to survive entirely without oxygen. These tiny creatures have been found in the sediments of anoxic (oxygen-free) basins like the L’Atalante basin in the Mediterranean Sea. Loriciferans derive their energy from hydrogen sulfide, a noxious chemical common in their environment, utilizing it instead of oxygen through a process known as anaerobic respiration.

2. Henneguya salminicola The Oxygen-Averse Parasite

salmon
Sockeye Salmon swimming in shallow waters. Image by Milton Love, Marine Science Institute, University of California, Santa Barbara, CA 93106, Public domain, via Wikimedia Commons

Henneguya salminicola, a close relative of jellyfish and corals, is a unique multicellular parasite that infects salmon and other fish. Unlike any other multicellular organism known, H. salminicola lacks mitochondria, the organelles responsible for aerobic respiration, indicating that this creature has entirely eliminated oxygen from its metabolic processes. Instead, it survives as a parasite within its host’s tissues, extracting nutrients directly from them, effectively outsourcing its energy needs.

3. Spinoloricus sp. nov. Another Deep-Sea Wonder

Deep sea
The deep sea, image by NOAA Office of Ocean Exploration and Research, Deep-Sea Symphony: Exploring the Musicians Seamounts, Public domain, via Wikimedia Commons

Spinoloricus is another member of the Loricifera phylum living in anoxic underwater environments. It was discovered alongside other Loriciferans in the L’Atalante basin and represents one of the few known examples of metazoans (animals with multiple cells) living permanently in an oxygen-free zone. Spinoloricus has developed an array of cellular adaptations to thrive in its challenging habitat, including organelles known as hydrogenosomes that replace mitochondria for energy production.

4. Osmolyte-Rich Brine Shrimp

brine shrimp
Brine shrimp. Image via Depositphotos

Brine shrimp, commonly found in saline lakes and brine pools, have an impressive resilience to extreme environmental conditions, including low oxygen concentrations. During times of stress, such as when encased in tiny brine pools where oxygen levels are depleted, brine shrimp enter a unique state called anoxia-induced quiescence, slowing down their metabolism to survive. It’s not a complete absence of oxygen dependence, but their ability to endure low-oxygen states for durations exemplifies incredible adaptability.

5. Naked Mole-Rat The Mammalian Exception

naked mole rat
Naked mole rat. Image via Depositphotos.

Naked mole-rats, native to East Africa, are renowned not only for their bizarre appearance but also for their unusual adaptation to low-oxygen environments. These mammals can endure much lower oxygen levels than other mammals can tolerate by dramatically lowering their metabolism and heart rate. When deprived of oxygen altogether, naked mole rats switch their primary metabolic pathway to one that utilizes fructose, similar to plants, enabling them to survive for short periods without oxygen.

6. Tubeworms The Hydrothermal Vent Residents

Spiny tubeworms
Avenue, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons

Tubeworms found near hydrothermal vents in the ocean need so little oxygen that they can survive in environments where oxygen is almost absent. These fascinating creatures harness the power of symbiotic bacteria living within their tissues and thrive on hydrogen sulfide emitted by the vents. The bacteria convert the sulfide into energy for the worms through chemosynthesis, illustrating a life-forging relationship independent of the sun-driven cycle of photosynthesis.

7. Certain Nematodes The Survivors in Hostile Soils

A fossilized nematode.
A fossilized nematode. Image by Ghedoghedo – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6683629

Nematodes are among the most ubiquitous organisms on Earth, with species found from the deepest oceanic trenches to the highest mountains. Some nematodes are incredibly resilient, and capable of surviving extreme environmental conditions, including anoxia. They accomplish this through a reversible metabolic state called cryptobiosis, during which their metabolic processes shut down almost entirely, allowing them to survive prolonged periods without oxygen until better conditions return.

Conclusion

tardigrade
Soil microorganisms including nematode, microarthropods, micro arthropod, tardigrade, and rotifers a soil sample, soil fungus and bacteria on a regenerative farm in compost under the microscope in australia. Image via Depositphotos.

As fascinating as it is to imagine life free of oxygen, the existence and survival of these remarkable anaerobic animals demonstrate the sheer adaptability and resilience of life. From the crushing depths of the ocean to the arid soils of the Earth, these organisms have evolved impressive physiological and metabolic mechanisms that allow them to thrive where few others can. They remind us of the incredible complexity of life and its ability to conquer even the most extreme environments.