Why Fish Need Oxygen Masks, Too

Remember the jumbo squid? A new study in Science suggests that the squid’s spread—they’re moving up and down the Pacific Coast in both North and South America—might be explained by the expansion of low-oxygen waters, which squid can tolerate. Of course, the expansion of low-oxygen, or hypoxic, water affects far more than squid: It potentially endangers fisheries around the world. That’s because, well, fish get picky about oxygen: When its levels drop, they die.

But let’s review. We’re used to hearing about hypoxia off the Gulf Coast or at the mouths of major rivers—that’s caused when nitrogen runoff (from fertilizer, principally) produces oxygen-hogging algae blooms. This is very different: Scientists believe that these deep-water hypoxic zones are caused by warming waters, which simply hold less oxygen. (An author of the paper uses a bottle of soda water as an example: “If you open it warm, it’ll fizz all over the place. If you open it cold, it will slowly fizz out as it warms.”) The Science paper looks at decades of oxygen data from the deep ocean: In the Atlantic just south of Africa, for example, the hypoxic layer, which suffocates most marine life, almost doubled in thickness over the last half century. In short, this may ultimately be a major problem for fisheries, and for us fish-eaters, and it likely won’t be fixed until the climate’s fixed, too.

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