Tiny Antarctic Krill Benefit the Planet in Big Ways, but Face a Barrage of Threats

A single Antarctic krill is about the size of your pinky finger. But with an estimated population of more than 700 trillion in the Southern Ocean, the tiny crustacean’s collective impact across the entire planet is enormous.

Their swarms are so massive they can be seen from space. They’re food by the millions for seals and penguins and whales. And they sequester huge amounts of carbon—more than $15 billion worth per year, according to the World Wide Fund for Nature (WWF).

Increasingly, though, Antarctic krill face threats from warming seas and a growing fishery. Scientists say that without international action to bolster marine protected areas and combat climate change, krill populations—and the resulting carbon sequestration—could drop off sharply in the coming decades.

Antarctic krill act as one of the world’s largest “biological pumps,” a term scientists use to describe the process by which marine organisms send carbon to the depths of the ocean, where it can be stored for hundreds of years. A study published last September in Nature Communications found that Antarctic krill sequester similar amounts of carbon to coastal marshes, mangroves and seagrass, habitats scientists consider some of the planet’s most prolific carbon sinks.

Krill feed on phytoplankton, which, like land-based plants, consume carbon dioxide and release oxygen as they photosynthesize. When krill waste sinks to the bottom of the ocean, all that carbon goes with it, essentially locking it away and freeing up space at the surface for more carbon to be absorbed from the air.

“Krill are, by fact of life, living and molting and pooping and dying, and all that is very important to bring carbon from the surface ocean to the deep sea,” says Matthew Savoca, an ecologist at Stanford University. “When krill are doing that at the population level, they end up being an important ally in the climate change fight.”

But Antarctic krill also face a host of challenges, including from warming oceans and an emboldened fishing industry, that researchers say require urgent attention. A study led by researchers at the British Antarctic Survey, published in Marine Pollution Bulletin this past December, found that an increase in plastic pollution in the Southern Ocean could inhibit krill’s ability to sequester carbon by 27 percent.

While the sheer number of krill in the Southern Ocean means the species is unlikely to face an acute threat to its survival in the near term, Savoca is quick to point out that numbers are no guarantee of success.

“You only have to look as far as our own country for the story of passenger pigeons to show you how quickly something can go from being incredibly abundant to extinct,” he says.

The Commission for the Conservation of Antarctic Marine Living Resources, which regulates fishing activity in the Southern Ocean, failed at a meeting last October to renew a key measure aimed at preventing excessive krill harvests in any one area. The commission, which makes decisions by consensus among its 26 member states and the European Union, has been at a yearslong standstill over that measure and several proposed marine protected areas amid opposition from China and Russia.

The result, says Zephyr Sylvester, an environmental researcher at the University of Colorado Boulder, is that fishing vessels are free to act on their companies’ directives until a new regulation is adopted. The lack of enforcement could allow the fishery to concentrate operations in a smaller area where it would have a larger environmental impact, she says.

Krill are used in products ranging from nutritional supplements to livestock feed, and the WWF estimates the Antarctic krill fishery to be worth about $250 million annually.

“We’ll learn a lot about the integrity of the fishery” now that the conservation measure has lapsed, Sylvester says, adding that external pressure, like the diplomatic and public awareness campaign in support of the Ross Sea Region Marine Protected Area a decade ago, remains among the most effective methods to turn scientists’ recommendations into policy. Still, she says, “it shouldn’t be the burden of consumers to enforce sustainable fishing practices.”

At the same time, declining sea ice is exacerbating challenges for Antarctic krill from the earliest stages of life. Krill larvae don’t have the lipid reserves of adult krill to get through the dark Antarctic winter, says Hauke Flores, a marine biologist at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany. Instead, larvae stick to the sea ice, feeding on ice algae until the sun—and the phytoplankton—returns in spring.

“Sea ice is critically important for Antarctic krill,” Flores says. “Without these algae that grow inside the sea ice, they will simply not survive.”

The Antarctic Peninsula, which juts northward and where huge numbers of krill are concentrated, is warming five times faster than the global average, according to research backed by the National Science Foundation. As a result, scientists say, krill may be concentrating farther south in search of more stable sea ice. A 2023 study in Nature Reviews Earth & Environment found that changes in the distribution of krill around Antarctica, driven by warming waters, threatened to increase interactions between fishing vessels and the animals that feed on krill, such as whales and penguins.

The study’s lead author, So Kawaguchi, a krill ecologist at the Australian Antarctic Division, says scientists are still trying to understand exactly how climate change will affect Antarctic krill. From his lab in Tasmania, where he has a research aquarium filled with 20,000 krill, Kawaguchi has shown that, if carbon emissions remain unchecked, krill hatch rates in parts of the Southern Ocean could decrease by 70 percent within the next century.

But he cautions that the effort to decode Antarctica’s shifting marine ecosystems is still in its early stages.

“There are lots of other things we need to consider,” he says. “It’s just the start.”

Gabe Castro-Root | READ MORE