At Swoop, we spend a lot of time talking about Antarctica’s wildlife, from many species of penguins to seals and amazing whale watching. These are the big charismatic animals that draw expedition cruise travellers to the end of the Earth. But there is one species that’s rarely on people’s draw cards, arguably the most important of all, because without it there would simply be no wildlife to see: the Antarctic krill.
On August 11, we celebrate World Krill Day to shine a spotlight on this humble crustacean. In previous years, we’ve looked at why krill sit at the centre of the Antarctica ecosystem and the potential threats posed by the growth of commercial krill fishing. This year, we spoke to Dr Emma Cavan, a marine biogeochemist at Imperial College London, about her research on the unexpected role that krill plays in storing carbon in the deep ocean, and what that means for our changing climate.
Krill for carbon storage
The Antarctic krill, or Euphausia superba, might be small in size, but everything else about them is colossal. Measuring around 5cm or two inches in length, they dine out on the diatoms, copepods and phytoplankton that proliferate in the Southern Ocean, and form swarms of such size that it’s hard to comprehend. A krill swarm can consist of perhaps 30 trillion or more individuals, and stretch kilometres in length.
As well as providing a food source for everything from fish all the way up to the largest whales, it’s long been known that krill also play a role in trapping carbon from the atmosphere and locking it away on the ocean floor. But it’s only now, thanks to new research by Dr Cavan and her team, that the extent of this climate engineering is becoming fully understood.
‘Krill are low down in the food chain and feeding directly on things that have consumed or converted atmospheric carbon, and convert that into their biomass,’ she explains. After feeding, the krill swarms produce vast amounts of poo. ‘These faecal pellets can sink at hundreds of metres per day, so very quickly they can get into the deep ocean.’
Krill poo isn’t the only carbon-rich byproduct from these enormous swarms. During the Antarctic summer, krill moult and shed their exoskeletons every 10-14 days, which also quickly sink to the ocean floor. This rain of krill byproducts effectively takes this carbon out of the natural biological cycle playing out at the ocean surface – once the krill poo and the exoskeletons are far below the surface, the carbon they contain is effectively locked away in deep storage. They only need to sink to about 300 metres deep to have their carbon removed from the system for over a hundred years
Cavan’s research has for the first time put numbers to this crustacean’s extraordinary carbon storage capabilities. Every year, Antarctic krill can store at least 20 million metric tons of carbon in the deep ocean. If the international markets traded in krill in the same way as carbon credits, that puts their value at anything up to US$ 46 billion. That’s an astonishingly big effect for such a tiny creature.
Protecting blue carbon
The name given to this carbon that is captured by the world’s oceans is blue carbon, and the numbers show that the value provided by krill is equivalent to well-known marine habitats such as mangroves, seagrass and salt marshes. But whereas these habitats consist of complex ecosystems, krill’s blue carbon is being captured by a single species, making it uniquely powerful as well as uniquely vulnerable.
A hundred years ago, the waters around Antarctica were the hunting grounds for industrial whaling, and research has suggested that the collapse of whale populations in the 20th century may have led to a similar decline in krill numbers. Now that whale numbers are starting to recover, they’re increasingly competing for krill with commercial fisheries. There is a big market for Antarctic krill for use as feed for aquaculture and – in the form of krill oil – as health food supplements. Although the global catch remains relatively small, this year’s record catch led to the 2025 fishing season being closed early.
It’s a concern for scientists. ‘At the moment we haven’t quantified what the impact of the krill fishery is having on the krill carbon sequestration, but obviously the krill fisheries are removing adults which could affect the future spawning and future population in subsequent years,’ said Cavan. As the fishing fleets become more efficient, they find it easier to target the biggest swarms which are also the biggest sources for blue carbon storage. Krill are facing a double challenge: while adults are chased by fishing fleets, warming sea temperatures in the Southern Ocean are threatening the sea ice formation that krill larvae depend on for their early development. It’s a tricky tightrope.
International efforts to tighten regulations around krill fishing in the Southern Ocean have stalled in recent years, but it is hoped that this new discovery of the important role they play in carbon capture can be used to affect fishing policies to reduce fishing – and possibly even lead people to reconsider their consumption of products using krill.
Where Cavan sees hope is while krill are individually small, they also seem uniquely engaging to many. ‘When I was working on the biological carbon pump, I couldn’t get people engaged – when you talk about zooplankton or copepods, nobody really cares. But people seem more interested in krill because they feed whales and penguins, and they’re a great way of telling the story of how the ocean stores carbon.’
On this World Krill Day then, we are singing the praises of this humble crustacean. They don’t just feed some of our favourite Antarctic wildlife, but they also play an incredible role in the Southern Ocean in terms of carbon storage – a reminder that protecting the ends of the Earth isn’t just about looking after a precious ecosystem, but also about safeguarding its role in regulating our planet’s carbon cycle. All hail the mighty krill – and their carbon-capturing poo!
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