ANTARCTIC KRILL: THE TINY CREATURES THAT KEEP WHALES ALIVE

In the vast, cold waters of the Antarctic, a remarkable relationship is playing out.

Tiny, translucent creatures called krill drift with the currents in dense, shifting swarms. Beneath them, whales – the largest animals on Earth – move with purpose, rising and diving through the same waters – feeding, travelling and surviving.

It’s easy to think of the ocean as just an endless expanse. But it is a complex system, built on relationships like this – where very different species rely on each other to keep everything in balance.

At the heart of the Southern Ocean ecosystem is the connection between krill and whales. For all their size and power, most whales depend on something no bigger than your little finger.

Fast facts: what are Antarctic krill?

• Krill are small, shrimp-like crustaceans found in the Southern Ocean.
• They feed on microscopic phytoplankton that bloom around Antarctic sea ice.
• These animals form dense super-swarms that can span tens of kilometres and are visible from space.
• Krill are a primary food source for many whales, seals, fish, penguins and seabirds.
• Climate change and industrial fishing are placing increasing pressure on krill populations.
• More than 6 tonnes of krill are needed to produce 1 tonne of krill meal used to feed farmed fish.

How krill support life in the Southern Ocean

To understand the relationship between krill and whales, we need to look at what sustains krill in the first place.

In Antarctic waters, life begins with something almost invisible. Each summer, as sunlight returns to this polar region, microscopic plants called phytoplankton bloom around the sea ice. Brief pulses of life in an otherwise extreme environment, these blooms are often so expansive that they are visible from space.

Phytoplankton draw energy from the sun and are the starting point of the food chain that supports marine life. They also produce much of the oxygen we breathe and absorb carbon dioxide from the atmosphere. But phytoplankton are too small and dispersed for whales to feed on directly. Krill bridge this gap by eating the phytoplankton and becoming a nutrient-rich food source for whales and other Southern Ocean wildlife.

In this way, krill are a crucial link in the food web for much of the region’s wildlife – not just whales but also seals, penguins, seabirds and some fish. It is estimated that there are over 700 trillion adult Antarctic krill – a collective biomass of between 300 and 500 million tonnes. This might sound like a lot, but to put it in perspective, one single blue whale is thought to consume up to 6 tonnes of krill per day!

All this energy moving through these waters shapes an ecosystem that has evolved over millions of years – finely balanced and deeply interconnected.

For baleen whales – large whales that filter tiny prey from the water using comb-like plates instead of teeth – the relationship is especially critical. Species like Antarctic blue whales, fin, humpback and minke whales rely heavily on krill during the feeding season to build the energy reserves they need for migration, breeding and survival.

Whale migratory journeys are extraordinary in scale, stretching thousands of kilometres across entire ocean basins. But this journey hinges on something deceptively simple: that when whales arrive to feed in the cold southern waters, the krill they need for energy will be there.

Why krill are under pressure

That expectation is becoming less certain.

Krill populations are increasingly under threat from two overlapping forces: climate change and commercial fishing.

Warming ocean temperatures and declining sea ice are already affecting krill populations. Sea ice provides essential food and shelter to juvenile krill, so as it melts, fewer krill survive to adulthood. In addition, rising carbon dioxide levels are making the ocean more acidic, further affecting vulnerable young krill.

At the same time, demand for krill is growing, driving commercial fishing. It is used to feed farmed fish and produce krill oil for supplements – a market expected to grow by around 10% each year until 2031.

Commercial krill fishing is managed by an international body – the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) – and there are catch limits in place. But concern is growing among scientists and conservation organisations that the current rules are not enough to protect this crucial food source, particularly in our rapidly changing climate.

The issue is not only how much krill is being taken, but where and when it is taken. Krill fishing is increasingly concentrated in the same feeding hotspots used by whales, often during summer when whales are building the fat reserves they need for migration and breeding. Fewer krill in these areas can have a serious impact on the whales that depend on this food. Research from the University of California linked reduced krill supplies in the Antarctic Peninsula to lower pregnancy rates in humpback whales, as females were less able to get the nutrients needed to sustain a pregnancy.

If overfishing continues to occur in areas where rising sea temperatures are already having an effect, the combined impact could be critical – for krill populations and the whales that rely on them.

Why krill and whales matter to our planet

Krill are a keystone species of the Southern Ocean food web, supporting a wide range of species from whales and seals to penguins, seabirds and fish. Without enough krill, many species would be under threat, particularly baleen whales, including humpback, blue and minke whales.

This matters because whales themselves play an important role in maintaining a healthy marine ecosystem, and even a healthy planet. Whales feed on krill and other prey at depth – where nutrients like iron are more abundant – then return to the surface to breathe. In doing so, they bring these nutrients back into sunlit waters through their waste products, which fuel phytoplankton growth. Since phytoplankton produce oxygen, absorb carbon dioxide and feed species like krill that sustain marine life, whales indirectly help to keep our oceans functioning and the climate in balance.

This means whales are not just part of the ocean. They help maintain its health. And their ability to do that depends on the availability of krill.

If the health of our oceans matters to you, you can help support WWF’s work to protect them.

How WWF is protecting krill in the Southern Ocean

Because krill are small and often overlooked, their importance is easy to underestimate. Not only do they play a key role in the waters around Antarctica, but they even help keep carbon out of our atmosphere. When krill eat phytoplankton, they produce fast-sinking waste that carries carbon deep into the ocean, where it is stored for many years.

Protecting krill means safeguarding the entire system that depends on them – from whales and penguins to the ocean itself.

That’s why WWF-Australia is working to protect krill by sharing scientific research, advocating for stronger fisheries management and calling for better ocean protection.

We work closely with scientists to understand how krill populations are changing, where they are most vulnerable and what’s needed to keep this vital food source available.

By using our political influence and partnerships, we are helping improve how krill fishing is managed. This includes advocating for catch limits in specific areas, reducing pressure on feeding hotspots, and ensuring decisions take into account the impact of climate change.

Unfortunately, recent negotiations by CCAMLR failed to renew limits on the amount of krill that can be taken from individual locations around the Antarctic Peninsula. This is putting significant pressure on krill in main feeding zones, within an ecosystem already under strain from climate change. In response to this mismanagement of the Antarctic krill fishery, WWF is seeking an immediate pause on krill fishing and has lodged an objection with the Marine Stewardship Council (MSC).

We are also pushing to protect the Southern Ocean through a network of Marine Protected Areas including fully protected marine sanctuaries.

These solutions will give our oceans the space they need to recover, so they can continue supporting life – including our own.

There is still time, but we need to act now.

How you can help protect our oceans

The health of the ocean is not built on any one species, but on the relationships between them.

Over millions of years, these connections have evolved into a finely tuned system – supporting everything from microscopic phytoplankton to blue whales, the largest animals on Earth. The relationship between krill and whales plays a central role in the Southern Ocean, and the growing pressure on krill is a reminder of how easily these interdependencies can begin to unravel.

By supporting WWF, you can help protect our oceans and ensure krill remain available to the species that rely on them.