- Antarctic krill trap vast amounts of carbon from the atmosphere in the ocean floor through their sinking fecal pellets, a new study reports.
- The annual amount is similar to that stored by “blue carbon habitats” such as mangroves, seagrass and salt marshes, highlighting the importance of protecting krill.
- Global warming, melting ice and overfishing pose threats to krill, say researchers who call for new fishing policies to conserve them.
In the icy waters surrounding Antarctica, small shrimp-like crustaceans called krill (Euphausia superba) swim in swarms of trillions, forming a biomass larger than the entire human population. Scientists knew these 5-centimeter-long creatures could trap carbon from the atmosphere in the ocean floor, but were unaware of the sheer scale.
New research has now revealed just how much: Krill can store at least 20 million metric tons of carbon in the deep ocean annually. This equates to $4 billion to $46 billion, depending on the price of carbon. Krill achieve this feat through their sinking fecal pellets, which preserve the carbon for more than a century.
“Krill are super-efficient in carbon sinking, [since they have] larger fecal pellets than other plankton,” said the study’s lead author, marine biogeochemist Emma L. Cavan of Imperial College, London. She and her colleagues reported their findings recently in Nature Communications.
In the Southern Ocean, krill serve as an important link in the food web, connecting microscopic plants called phytoplankton to a range of marine animals, from penguins and seals to fish and squid. Even the humongous blue whales depend on them. They swim in super-swarms that can span ten kilometers in width and a hundred meters in depth—so huge that their nighttime bioluminescent glows make them visible from space.
Cavan and her team estimated the density of krill in the ocean by using KRILLBASE20, a database containing 90 years of historical data. They multiplied this number by the rate at which krill produce carbon in their fecal pellets. This gave them the total amount of carbon held by krill in the upper ocean, which is about 20 meters deep.
To determine how much of this carbon flux is sequestered, or stored for long periods of time, the researchers used an ocean circulation model to show for the first time that krill fecal pellets can lock up carbon for more than 100 years even without needing to sink to great depths.
Finally, the team used the social cost of carbon dioxide to convert these amounts into monetary equivalents. That provides a better comparison between carbon storage by krill and by “blue carbon habitats” of rich coastal ecosystems, such as mangroves, seagrass and salt marshes—which can also store carbon for a century or more.
Until now, Cavan noted, Antarctic krill had not been part of this conversation. “For the very first time, we have defined their prominent carbon storing capacity as ‘blue carbon,’ which opens up a new, important reason to protect these crustaceans and their habitats,” she said.
Today, krill face dire threats from warmer waters and heavy fishing. Krill catch by the fishing industry brings in about $0.3 billion each year. Lobbying by this industry is intense: In October, the Commission for the Conservation of Antarctic Marine Living Resources, an international conservation body responsible for protecting Antarctic ecosystems, failed to roll back regulations of heavy krill fishing despite a year of negotiations.
But as ice melts and water warms, larval krill struggle to survive, said Cavan, contributing to their population decline. Huge international fishing hauls only add to their struggle for survival.
“Now that we can quantify the massive carbon storage by krill, I hope this will affect fishing policies, urge fisheries to reduce krill fishing, and help the public in reducing consumption of krill-based products,” she said.
The fate of krill in decades to come is uncertain, said Chelsey Baker, an ocean biogeochemical model analyst at the National Oceanography Centre, Southampton, U.K.
“It is currently unclear how future changes, such as expanded fisheries or climate-driven changes, will impact Antarctic krill populations and in turn their potential to store carbon,” said Baker, who was not involved in the study.
She hopes the work by Cavan’s team will raise awareness of this role and encourage policymakers to develop regulations to protect these ecosystems.
Citation:
Cavan, E.L., Mackay, N., Hill, S.L. et al. Antarctic krill sequester similar amounts of carbon to key coastal blue carbon habitats. Nature Communications 15, 7842 (2024). https://doi.org/10.1038/s41467-024-52135-6
Farah Aziz Annesha (@fazizann22) is a graduate student in the Science Communication M.S. Program at the University of California, Santa Cruz. Other Mongabay stories produced by UCSC students can be found here.
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