Small, but mighty important

Small, but mighty important

I vividly remember the moment back in Tokyo when I first borrowed an encyclopedia about zooplankton from my primary school science teacher and ran back home. I begged my parents to buy a microscope, turned my mum’s stocking into a plankton net, and every day enjoyed looking at all kinds of plankton collected from nearby ponds and rivers. My childhood interest in plankton led me to study fisheries science at university.

Antarctic krill.
Antarctic krill. Credit: Brett Wilks

After completing my PhD in 1990 I joined a Japanese fishing company as a research scientist. New recruits were often challenged by being sent to sea for several months, in my case to the Southern Ocean, fishing for Antarctic krill. The boat was trawling round the clock, landing enormous amounts of krill on the deck. This was my first encounter with krill – I fell in love and wanted to know more about their role in the ecosystem. After working for the Japanese Fisheries Research Agency, I made a big move in 2002 and joined the Australian Antarctic Division in Hobart – the best place in the world to study krill – to lead the world’s only experimental krill research aquarium.

The Southern Ocean is the planet’s shock absorber. Without its ability to absorb heat and carbon dioxide (CO2), the world’s future climate would be even more variable. As the world’s most abundant multicellular animal, krill are understood to play an important role in this climate regulation. Vast swarms of krill graze on the phytoplankton that fix CO2 into organic compounds. Krill faeces sink rapidly to the deep ocean, accelerating the process of removing carbon from the atmosphere and locking it away. There is also evidence that the daily migrations of krill swarms, up and down from the depths, stir the ocean and bring nutrients to the surface to fertilise more phytoplankton blooms.

The rv investigator.
The RV Investigator. Credit: CSIRO Marine National Facility

Krill are also crucial as food that sustains the Southern Ocean icons, the great whales and penguins. At the same time, krill are the target of the largest fishery in the Southern Ocean. While the amount of krill currently being harvested is still small compared to their total biomass, this fishery is growing. As human populations rise and food security becomes an increasing priority, there will be intense pressure to expand the krill fishery.    

But for a super-organism so essential to the ecological functioning of the Southern Ocean, there are still fundamental things we don’t understand about krill. We know that they are very abundant, but we don’t know with sufficient accuracy how many there are now or if their populations are increasing or declining. We know they use sea-ice as a habitat, but much of their life remains a mystery especially during winter when covered by sea-ice.

The Southern Ocean is the planet’s shock absorber.

The increase of anthropogenic CO2 is causing climate change and making the seawater more acidic. Parts of Antarctica are showing rapid warming, causing seawater temperatures to rise and changes in sea-ice dynamics.

The Southern Ocean is often referred to as a window to the future environment. With a relatively simple food web compared to many other regions, any effects of climate change at any level of the food web are more likely to cascade throughout this ecosystem and be more immediately apparent.

How will the Southern Ocean ecosystem look in the future? Will there be enough krill for whales, seals and penguins? How can we ensure a sustainable krill fishery into the future?

Our next big thing is for the scientific community to make a collective effort to better understand this precious ecosystem from the perspective of krill.

Examining krill on the investigator.
Examining krill on the Investigator. Credit: Andreas Klocker

A major breakthrough in krill husbandry techniques has meant the entire lifecycle successfully occurs in our aquarium at the Australian Antarctic Division, allowing experimental studies on all stages of krill under a range of controlled environments.

Our recent studies have focussed on the impacts of climate change and ocean acidification on krill and the implications for the Southern Ocean. We have shown that if carbon emissions and ocean acidification continue unabated, krill reproduction and development could be significantly reduced by 2100 and the entire Southern Ocean krill population could collapse by 2300.

While land-based laboratory research is an invaluable tool, we also conduct extensive field work. I recently led a major krill research campaign to the Antarctic ice edge on the CSIRO research vessel Investigator during January-March 2021, to fill some important gaps in our knowledge of the krill ecosystem.

How can we ensure a sustainable krill fishery into the future?

We recently used cutting-edge technology to observe wild krill at sea. For the first time, a coupled video-echosounder system enabled the visualisation of krill swarms in three dimensions. We lured deep-sea krill with lights to a camera and trap to understand their distribution at the seafloor.  We designed autonomous moored observatories that we deployed to the seafloor to record the abundance and behaviour of krill throughout a full year. We have never had this information before – these devices will observe krill as the sea-ice grows above them during the dark of winter and as it retreats during the following spring.

This fundamental information will improve our understanding of krill and how best to manage the impact of climate change and fishing pressure on their populations, and ultimately, to conserve the food source of the predators that depend on them.

This new research will be fascinating. The extraordinary life of the Southern Ocean – and the ecological health of the planet – deserve nothing less.

* Read more about the recent voyage here.

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