We have a surprising underwater ally in combatting climate change: zooplankton

Odds are you aren’t too familiar with the group of animals called zooplankton, which include copepods, krill and salps. On land, they’re most commonly used as fish food. Underwater, however, they’ve been quietly making a substantial contribution to slowing global warming. The reported on the latest research into zooplankton by an international team, published in the journal , that detailed just how much these tiny critters have been impacting the planet’s temperature.

In the spring and summer time, the animals consume phytoplankon, which are photosynthesizing bacteria and organisms that live on the ocean’s surface. After gorging themselves on this feast, zooplankton descend into the deeper waters around Antarctica to hibernate and burn off the fat created by eating phytoplankon, which releases carbon dioxide. This behavior has had the added benefit of storing carbon hundreds of meters underwater, where it can take decades or sometimes centuries to re-emerge and add to warming the atmosphere.

“If this biological pump didn’t exist, atmospheric CO2 levels would be roughly twice those as they are at the moment,” co-author Professor Angus Atkinson from Plymouth Marine Laboratory told the BBC. “So the oceans are doing a pretty good job of mopping up CO2 and getting rid of it.”

It was already known that zooplankton played a role in facilitating carbon storage, but the new results detailed just how effective these aquatic critters have been in helping slow the planet’s warming. They said zooplankton are responsible for transporting 65 million tons of carbon each year to the depths of the Southern Ocean. That’s the equivalent of a year’s emissions from 55 million diesel cars.

But since we seem incapable of having nice things, zooplankon are also at long-term risk. The climate change that they have been helping to stave off poses a threat to these species in the form of higher water temperatures, disturbances to ocean layers and extreme weather events. There’s also an industry for krill harvesting; according to the UN, about 500,000 tons of krill were removed from the ocean by commercial operations in 2020.