Krill’s role in carbon sequestration amazes scientists

Antarctic krill are likely amongst the world’s most important carbon-storing organisms, according to a new study published in the influential Nature Communications journal. The findings, after a decade of research, have amazed the team behind the evaluation.

The researchers estimate that Antarctic krill (Euphausia superba) annually lock at least 20 million tonnes of carbon into the deep ocean.

These estimates put krill on a par with key coastal habitats such as saltmarshes, mangroves, and seagrasses, which sequester 13, 24 and 44 million tonnes of carbon per year, respectively. These areas are increasingly being placed in conservation zones due to their role in greenhouse gas reduction and habitat survival.

But Antarctic krill are being impacted by rapid climate change and expanding fishery activity, bringing the researchers to conclude that krill and their habitat need to be protected.

Marine life is known to play an important role in locking carbon away from the atmosphere in ocean systems, known as ‘blue carbon’. And, while coastal vegetation dominates blue carbon research and policy, the new findings shine the spotlight on the role of animals in the open ocean.

Lead author of the paper,  Dr Emma Cavan, from the Department of Life Sciences at Imperial College London, UK,  says: “For the past decade we have been piecing together the role krill have in carbon cycling, finally resulting in this amazing finding that krill, and their poo, store similar amounts of carbon as some coastal marine plants.

“I hope this means we can now work towards conserving krill and their valuable Southern Ocean ecosystem with the same gumption as we are seagrasses and mangroves.”

Antarctic krill provide an important food source for animals such as whales, seals, and penguins. They are small crustaceans (about 6cm) found in the seas surrounding Antarctica, where they can form swarms of up to 30 trillion individuals.

The krill eat phytoplankton – tiny plant species that use carbon from the atmosphere to perform photosynthesis. The carbon, trapped in the krill’s faecal pellets, then sink to the bottom of the ocean where it remains on the seafloor.

“One of the amazing things about krill is that they form massive swarms, which can be over a kilometre in length,” says co-author Dr Anna Belcher from the UK Centre for Ecology & Hydrology.

“This drives a huge ‘rain’ of krill poo after feeding, making krill globally important for locking carbon away from the atmosphere.”

They estimate that the krill’s fast-sinking faecal pellets need only reach a depth of around 380m for the carbon to be sequestered for 100 years.

The annual carbon sequestration for the entire circumpolar Antarctic krill population equates to about AUD $6 to $68 billion (USD$ 4 to 46 billion), depending on the price of carbon.

Given the additional significant amount of carbon in living krill, moulted exoskeletons, and carcasses, the researchers say it’s likely that Antarctic krill is amongst the world’s most important carbon-storing organisms.

But the krill face human-induced threats. Climatic warming is reducing sea-ice, an important habitat for krill larvae, and they are increasingly fished for bait, food, dietary supplements, and for use in aquaculture.

“Not only do they support unique, valuable and iconic species, but they are also key conduits for carbon storage,” the authors write.

“Both of these facets warrant the utmost importance of conserving into the future.”