Krill play a key role in carbon storage – plastic disrupts this process
Plastic pollution in the Southern Ocean may hinder the efficient transport of carbon bound by Antarctic krill to the deep ocean, with implications for the global carbon cycle and thus for global warming.
Antarctic krill, though only a few centimeters long, are essential to both the Southern Ocean and the entire Earth system: they form the backbone of the Antarctic food web, supporting fish, seabirds, penguins, whales, and seals, while also playing a crucial role in the global carbon cycle.
Krill play a vital role in exporting carbon to the ocean’s depths, where it is being locked away for long periods of time—an essential process in the fight against global warming. Carbon from the atmosphere is first used by phytoplankton for photosynthesis, which then serves as a primary food source for krill.
When the digested unicellular algae are excreted by the krill, the ingested carbon sinks into the depths in the form of countless fecal pellets. Each chitinous shell that has become too small, which the constantly growing krill regularly sheds every two to three weeks over its entire lifespan (up to six years), also transports carbon to greater depths. This entire process, which transports carbon from the atmosphere into the deep sea, is known as the “biological carbon pump”.
Krill occur en masse in the Southern Ocean in huge swarms of up to 30 trillion individuals – their total biomass is roughly equivalent to that of all humans on Earth – and thus make a decisive contribution to carbon storage, just like mangroves or seagrass meadows. This is also known as “blue carbon”, as it is sequestered by marine organisms.
According to a recent study published in Nature Communications in September 2024, krill lock at least 20 million tons of carbon into the deep ocean annually for at least 100 years and thus temporarily remove it from the cycle.
“This study shows how we as people are connected to a small creature in a remote location. We benefit from its actions in removing carbon but we also affect it through our own actions which drive climate change,” says Dr. Simeon Hill, researcher at the British Antarctic Survey and co-author of the study, in a press release from Imperial College London.
However, in another new study published in November in the journal Marine Pollution Bulletin, a British-Italian research team found that the export of carbon via krill fecal pellets could be hindered by plastic pollution in the Southern Ocean.
“Krill are an important part of the Southern Ocean food web and are the diet of penguins, seals and whales. We had already found plastic pollution in Antarctic krill from the Southern Ocean,” explains Clara Manno, marine ecologist at the British Antarctic Survey and lead author of the study, in a BAS press release. “But for the first time, we have evidence that plastic pollution could be reducing the ability of krill faeces to transport and store carbon in the deep ocean by over a quarter – this is huge! Now we can see that plastic pollution is disrupting the natural role that the ocean, and climate heroes like krill, play in balancing the global carbon cycle.”
In laboratory experiments, researchers discovered that faecal pellets degraded more rapidly by bacteria in seawater mixed with nanoplastics—microscopic plastic particles less than one hundredth the diameter of a human hair—compared to pure seawater.
This suggests that the amount of carbon transported to the deep sea by faecal pellets could decrease by 27 percent, or 5.5 million tons, per reproductive season due to the presence of plastic. As a result, a larger share of carbon would remain in the upper ocean, staying in the carbon cycle. This would reduce the efficiency of the biological carbon pump.
“Nanoplastics are invisible to the human eye but they can have a big impact in the environment. Understanding that it’s not just the animals themselves being impacted but their positive role in mitigating climate change really highlights the need for global action on the issue of plastic pollution,” says Emily Rowlands, marine ecologist at the British Antarctic Survey and co-author of the study.
Krill are already under pressure from ocean warming, acidification, and fisheries, all of which have implications for the carbon cycle. Given these existing threats, the authors stress the need to also address the impact of plastic pollution in international climate change mitigation and adaptation policies.
Julia Hager, Polar Journal AG
More about this topic:
