Australian scientists are closer to discovering more about the winter movements of Antarctic krill thanks to a not-so-subtle device.

Sitting on the seafloor near Mawson research station were two KOMBIs or Krill Observational Mooring for Benthic Investigation.

Resembling a big, bright yellow box, they had been quietly collecting data since they were deployed by teams on board the RV Investigator in January 2021.

Now the two KOMBIs are off the sea floor and back in the hands of scientists ready to trawl through mountains of information.

Biologist Dr Maddie Brasier said understanding what Antarctic krill do in winter has been notoriously difficult.

“In the summertime, we can go down there on a ship and study krill using sound, and we can also trawl for krill,” Dr Brasier said.

“But in winter we can’t get there because of the impenetrable sea ice.”

“So the KOMBI enables us to study krill all year round including that seafloor habitat that we can’t access.”

To do this, the KOMBIs are packed with lights and cameras that activate every five hours to record a short burst of sea floor footage, as well as an echo sounder to measure the biomass of krill above.

Rounding out the on board technology is an high definition audio recorder developed and built by the AAD Technology and Innovation team, which is capable of recording more than a years’ worth of calls made by seals and whales, which are key predators of Antarctic Krill.

X marks the spot

Dr Brasier led the effort to locate and retrieve the KOMBIs and was part of the original team to deploy them in 2021.

Chartered icebreaker, Aiviq honed in on the GPS coordinates during its voyage to changeover expeditioners at Mawson station.

A signal was then sent to the KOMBIs to drop their anchor weight and float to the surface from depths of 800 and 1200 metres.

“We came alongside the KOMBI, grappled it and then hoisted it with a crane back onto deck,” Dr Brasier said.

“There was definitely a competition to see who saw it first. We had expeditioners all around the vessel trying to spot the KOMBI, and there were prizes for the winners.”

The KOMBI also picked up a ‘hitchhiking’ octopus, which was gently persuaded to return to the sea.

Downloading from the deep

Sifting through hours of echo sounder data is the task of fisheries acoustics scientist Dr Abbie Smith.

“An echo sounder produces a sound pulse through the water column and then the instrument will listen for the echoes that are returned,” Dr Smith said.

“They’ll bounce off anything that’s in the water column, be it krill, fish, ice, everything.”

It’s hoped the data will reveal krill biomass at depths beyond the reach of ships.

“Traditionally, methods used by ships are only able to measure acoustic data down to 250 metres for krill because of background noise issues associated with moving vessels,” Dr Smith said.

“Having these quiet moorings on the seafloor means that we’re going to be able to get biomass data for krill below this depth and figure out how much biomass we’re missing with ships alone.”

Thinking outside the box

Data from the KOMBIs could help guide the sustainable management of fisheries in the Southern Ocean.

Krill are a cornerstone species of the Southern Ocean food web, supporting penguins, whales and seals.

The species also play a critical role in carbon capture by consuming carbon-rich phytoplankton.

Their pellets then sink, taking carbon out of the surface ocean and pushing it deeper into the ocean while more carbon dissolves into the surface ocean from the atmosphere above.

The Australian Antarctic Division hopes to deploy the KOMBIs again in future years.