Around the world, wide swaths of open ocean are nearly depleted of oxygen. Not quite dead zones, they are “oxygen minimum zones,” where a confluence of natural processes has led to extremely low concentrations of oxygen.
Only the hardiest of organisms can survive in such severe conditions, and now MIT oceanographers have found that these tough little life-forms — mostly bacteria — have a surprisingly low limit to the amount of oxygen they need to breathe.
In a paper published by the journal Limnology and Oceanography, the team reports that ocean bacteria can survive on oxygen concentrations as low as approximately 1 nanomolar per liter. To put this in perspective, that’s about 10,000 times lower than what most small fish can tolerate and about 1,000 times lower than what scientists previously suspected for marine bacteria.
The researchers have found that below this critical limit, microbes either die off or switch to less common, anaerobic forms of respiration, taking up nitrogen instead of oxygen to breathe.
With climate change, the oceans are projected to undergo a widespread loss of oxygen, potentially increasing the spread of oxygen minimum zones around the world. The MIT team says that knowing the minimum oxygen requirements for ocean bacteria can help scientists better predict how future deoxygenation will change the ocean’s balance of nutrients and the marine ecosystems that depend on them.
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