On my second Antarctic voyage, a guide passed a small jar around the Zodiac. Inside, a single translucent, shrimp-like creature about the length of my little finger flicked its tail against the glass. “This,” she said, “is what every whale, every penguin, and every seal you have photographed this week is really here for.” She was right. Antarctic krill is the most important animal in the Southern Ocean, the keystone on which the entire spectacular food web rests, and understanding it changes the way you see everything else on the trip. This guide explains what krill is, why it matters so enormously, how it powers the whales and penguins, and why its future — and the fishery now targeting it — should concern anyone who loves Antarctica.
The short version: Antarctic krill (Euphausia superba) is a small swarming crustacean with one of the largest combined weights of any animal on Earth, and it is the primary food of the region’s whales, seals, penguins, fish, squid, and seabirds. It also plays a surprising and vital role in locking carbon away in the deep ocean. Almost everything that makes Antarctica’s wildlife so abundant traces back to this single species.
Antarctic krill: the keystone of the Southern Ocean
Ecologists use the word “keystone” for a species that holds an entire system together, and few animals deserve it more than Antarctic krill. It is the main prey of three species of whales, seven species of penguins, five species of seals, and a long list of fish, squid, albatrosses, and other seabirds. Remove krill from the equation and the whole edifice collapses: no krill, no whales, no penguin colonies, no leopard seals, no albatrosses behind the ship. It is genuinely no exaggeration to say that the abundance and accessibility of Antarctic wildlife — the very thing that draws travellers south — exists because of the extraordinary productivity of this one humble crustacean.
That is why I always encourage people to spend a moment thinking about krill rather than dismissing it as mere fish food. When you understand krill, the geography of the colonies, the timing of the whale season, and the behaviour of the seals all suddenly make sense, because every one of them is ultimately a story about following the krill.
What exactly is krill?
Antarctic krill is a crustacean, related to shrimp and crabs, growing to around six centimetres long and weighing about two grams — small enough to sit comfortably in the palm of your hand. It is semi-transparent, tinged pink and red by the pigments in its body and the algae it eats, with large black eyes and a pair of feathery limbs it uses to filter food from the water. Krill are bioluminescent, producing a soft blue-green glow from special organs, and a disturbed swarm can light up the dark water. They can live for around six years, which is remarkably long for such a small animal, and in hard times they can actually shrink, reabsorbing their own body tissue to survive a lean winter — one of the strangest survival tricks in the animal kingdom.
One of the largest biomasses on Earth
The single most staggering fact about krill is its sheer abundance. The total weight of Antarctic krill in the Southern Ocean is estimated at somewhere around 300 to 500 million tonnes, one of the greatest combined weights of any single wild species on the planet. They achieve this by gathering in immense swarms that can stretch for kilometres and reach densities of tens of thousands of individuals per cubic metre, turning the water pink or rust-red. Some swarms are so vast they can be detected from space. To float above such a swarm, knowing that millions of tiny lives are massed beneath your boat and that this is the engine of everything around you, is a quietly awe-inspiring experience.
The Antarctic food web: who eats krill
The simplest way to grasp krill’s importance is to look at who depends on it. The table below shows the main krill-eaters and how central krill is to each.
| Predator group | Examples | How much they rely on krill |
|---|---|---|
| Baleen whales | Blue, fin, humpback, minke | Almost entirely; several tonnes per whale per day in summer |
| Penguins | Adélie, chinstrap, gentoo and others | A major part of the diet, especially the ice-associated species |
| Seals | Crabeater, leopard, fur | Crabeaters are krill specialists; leopards eat much krill too |
| Fish & squid | Antarctic silverfish, various squid | Important prey, themselves eaten by penguins and seals |
| Seabirds | Albatrosses, petrels, Wilson’s storm petrel | Krill is a staple for many tube-nosed seabirds |
Whales and krill: the giant and the tiny
Nowhere is the krill connection more dramatic than with the great whales. A feeding blue whale — the largest animal that has ever lived — sustains itself almost entirely on krill, taking several tonnes a day during the summer feeding season by engulfing whole swarms in cavernous lunges. The recovering humpback and fin whales gather in their thousands precisely where the krill is densest, in the bays and straits of the Antarctic Peninsula. This is why a late-season whale-watching trip is so productive: you are really watching the krill harvest, with the whales as the harvesters. The full story of those whales is told in our guide to the whales of Antarctica.
Penguins, seals, and seabirds: the rest of the web
Beyond the whales, krill feeds the animals that define an Antarctic landing. The pink stain you see on the snow of every penguin highway is krill-rich guano — a literal map of what the colony has been eating. Adélie and chinstrap penguins in particular are heavily dependent on krill, which is why their fortunes track the krill so closely. Among the seals, the crabeater is a pure krill specialist, straining swarms through specially lobed teeth, and even the fearsome leopard seal takes a great deal of krill alongside its penguin prey. Add the albatrosses, petrels, and the tens of millions of Wilson’s storm petrels pattering over the swells, and you have an entire community — the one described across our guides to Antarctica’s penguins, the seals of Antarctica, and Antarctic seabirds — all ultimately fed by the same crustacean.
The life cycle of krill and its bond with sea ice
Krill’s life story is intimately tied to the sea ice, which is exactly why climate change is so worrying for the species. Adults spawn in summer, releasing eggs that sink hundreds of metres before hatching; the developing larvae then rise back toward the surface. Through their first winter, juvenile krill shelter beneath the sea ice and graze on the rich algae that grows on its underside — the ice is their nursery and their larder. Without enough winter sea ice, that crucial early-life habitat shrinks, and fewer young krill survive to adulthood. The dependence runs deep: the ice that defines Antarctica’s appearance is also, quite literally, the cradle of its food web.
What krill eat: the base of it all
If krill feed everything above them, what do they feed on? The answer is phytoplankton — microscopic floating plants — and the algae that blooms on and under the sea ice. Each spring, as the light returns and the ice melts, the Southern Ocean erupts in vast blooms of these tiny plants, and the krill graze them like cattle on a meadow. In this way krill convert the explosive but invisible productivity of the polar spring into a form that whales and penguins can eat. They are the essential link between sunlight and the giants, the step that turns sunshine into blubber.
Krill and carbon: an unexpected climate ally
Here is a fact that surprises even seasoned travellers: krill help fight climate change. As they feed near the surface and then sink to defecate at depth, and as they shed their carbon-rich moults, krill transport huge quantities of carbon from the surface into the deep ocean, where much of it is locked away in seafloor sediments for centuries. This “biological carbon pump” makes the krill swarm one of the planet’s significant natural carbon sinks. Together with the iron-rich waste of the whales that fertilises the phytoplankton, it forms a self-reinforcing loop in which the whole ecosystem helps regulate the global climate. The humble krill, it turns out, is doing the world a quiet and enormous favour.
Swarms, behaviour, and the science of counting krill
One reason krill is so successful is its swarming behaviour. By massing in dense aggregations, krill gain a measure of safety in numbers and improve their odds of breeding, even as the swarm becomes an irresistible target for predators. These swarms are dynamic, shifting with currents, light, and the presence of hunters, rising toward the surface at night and sinking by day in a daily vertical migration that is one of the largest movements of biomass on the planet. Counting them is a serious scientific challenge: researchers use ship-borne acoustic surveys that bounce sound off the swarms, net sampling, and increasingly environmental DNA — traces of genetic material in seawater — to estimate how much krill is present and where. Getting those numbers right matters enormously, because they underpin the catch limits that govern the fishery and the conservation of every predator that depends on krill.
Krill compared with its relatives
Antarctic krill is the most famous of more than 80 krill species worldwide, and it is by far the most important in the Southern Ocean, but it is not alone. Other species such as ice krill live farther south, closer to the continent, and become more important in the diet of animals in the high-latitude pack ice. What sets Antarctic krill apart is the combination of its large size, its astonishing abundance, and its habit of forming the dense, predictable swarms that make it such an efficient food source for large predators. In effect, the Southern Ocean has evolved around this one species, which is why scientists watch it so closely as conditions change.
The krill fishery and how it is managed
Krill is now harvested commercially, mainly for omega-3 krill-oil supplements and as feed for fish farms, and the fishery is the largest by tonnage in the Southern Ocean — it landed around half a million tonnes in 2024. It is managed by an international body, CCAMLR, which sets catch limits and area closures, and in a notable development the fishery reached its precautionary “trigger level” catch limit for the first time in August 2025 and was closed immediately. The central worry among scientists is that the fishery concentrates in the very same coastal bays and straits where whales and penguins feed, raising the risk of local competition for food precisely where the wildlife is densest. The debate over how to manage krill sustainably as both the climate and the fishery change is one of the most important conservation questions in Antarctica today.
Climate change and the future of krill
The longer-term threat is climate. As the Antarctic Peninsula warms and winter sea ice declines, the nursery habitat that juvenile krill depend on is shrinking, and there is evidence that the centre of the krill population is contracting southward toward the colder, ice-rich waters that remain. If krill decline or shift away from the traditional feeding grounds, the consequences would cascade upward through every predator that depends on them, from the Adélie penguin to the blue whale. Because krill sits at the base of the web, its fate is, in a very real sense, the fate of Antarctic wildlife as a whole. That is the sobering subtext behind every beautiful wildlife encounter described in our overview of Antarctica wildlife.
Can you actually see krill on a cruise?
Yes, in several ways, even though you are not going to go krill-spotting the way you watch for whales. Guides often net a sample to show passengers, so you can hold a living krill and appreciate it up close. You will see the evidence everywhere: the pink and red guano staining the penguin colonies, the rust-coloured patches discolouring the water where a swarm is dense, and occasionally krill spilling from the mouth of a lunge-feeding whale. On a calm, clear day you may even spot the shadow of a swarm beneath the surface. Once you know what you are looking at, the signs of krill are all around you, quietly explaining the entire spectacle. For how to make the most of these moments, see our guide to where to see wildlife in Antarctica.
Why krill matters to travellers
You might reasonably ask why a tourist should care about a two-gram crustacean. The answer is that krill is the single best lens for understanding Antarctica as a living system rather than a series of disconnected photo opportunities. Knowing that the whale, the penguin, and the seal are all chapters of the same krill story makes every sighting richer and more meaningful. It also makes you a better advocate: travellers who return home understanding the central role of krill are exactly the people who can speak up for the careful management of the fishery and the protection of the sea ice. In that sense, learning about krill is part of travelling responsibly, a theme that runs through our guide to Antarctica wildlife viewing rules.
Frequently asked questions about Antarctic krill
What is Antarctic krill?
Antarctic krill (Euphausia superba) is a small swarming crustacean, around six centimetres long, related to shrimp. It lives in the Southern Ocean, feeds on phytoplankton and sea-ice algae, and is the primary food source for the region’s whales, seals, penguins, fish, and seabirds, making it the keystone species of the Antarctic ecosystem.
Why is krill so important to Antarctica?
Because almost every larger animal depends on it. Krill is the main prey of three whale species, seven penguin species, five seal species, and countless fish, squid, and seabirds. It converts the microscopic productivity of the polar spring into food for the giants, so the entire abundance of Antarctic wildlife rests on it.
How much krill is there in the Southern Ocean?
The total biomass is estimated at roughly 300 to 500 million tonnes, one of the largest combined weights of any wild animal species on Earth. Krill achieve this through enormous swarms that can stretch for kilometres and reach densities of tens of thousands of individuals per cubic metre.
Does krill really help fight climate change?
Yes. By feeding at the surface and then sinking to deeper water to release carbon-rich faecal pellets and shed moults, krill transport large amounts of carbon into the deep ocean and seafloor sediments, where it is stored for long periods. This biological carbon pump makes the krill swarm a significant natural carbon sink.
Is krill fishing a threat to Antarctic wildlife?
It is a growing concern. The krill fishery is the largest by tonnage in the Southern Ocean and tends to concentrate in the same coastal areas where whales and penguins feed, raising the risk of local competition for food. It is managed by the international body CCAMLR, and in August 2025 the fishery hit its precautionary catch limit for the first time and was closed.
What do krill eat?
Phytoplankton — microscopic floating plants — and the algae that grows on and beneath the sea ice. Each spring the returning sunlight triggers vast blooms of these tiny plants, and krill graze them in enormous numbers, forming the link between sunlight and the larger animals.
Can you see krill in Antarctica?
Often, yes. Guides frequently net a sample so passengers can see a living krill, and the evidence is everywhere: pink krill-rich guano staining the penguin colonies, rust-coloured water where swarms are dense, and krill spilling from the mouths of feeding whales. You will not hunt for krill the way you watch for whales, but the signs are all around once you know them.
How long do krill live?
Antarctic krill can live for around six years, which is long for such a small animal. Remarkably, in times of food shortage they can shrink in size, reabsorbing their own body tissue to survive, then grow again when conditions improve — an unusual adaptation to the boom-and-bust seasons of the polar ocean.
Is krill a fish?
No. Krill is a crustacean, in the same broad group as shrimp, crabs, and lobsters, not a fish. The name comes from a Norwegian word for the small fry that whales eat. Krill have a hard exoskeleton, jointed legs, and the feathery filtering limbs typical of crustaceans.
Do humans eat Antarctic krill?
Mostly indirectly. The bulk of the harvest becomes omega-3 krill-oil supplements and feed for farmed fish and other livestock, rather than food eaten directly by people. A small amount is processed for human consumption, but krill’s main commercial value lies in its oil and as aquaculture feed.
What would happen if krill disappeared?
It would be catastrophic for Antarctic wildlife. Because krill is the primary food of the whales, penguins, seals, and many seabirds, a collapse would cascade up the food web, causing widespread declines among the very animals that make Antarctica such an extraordinary wildlife destination. This is precisely why protecting krill and its sea-ice habitat is so important.
When is the krill most abundant in Antarctica?
Krill swarms build through the summer as the spring phytoplankton blooms feed them, which is exactly why the whale-watching season peaks in late summer, from January through March. The richest feeding grounds form in the productive bays and straits of the Antarctic Peninsula, the same waters featured in our guides to the best time to visit Antarctica and Antarctica’s regions.
How does krill survive the Antarctic winter?
Juvenile krill shelter beneath the sea ice and graze on the algae growing on its underside, while adults can slow their metabolism and even shrink in size to endure the lean, dark months. This reliance on winter sea ice is why the decline of that ice with climate change is such a serious long-term threat to the species and everything that eats it.
Final thoughts
It is fitting to end a tour of Antarctic wildlife with the animal that makes all the rest possible. The whales, the penguins, the seals, and the seabirds are the stars of the show, but Antarctic krill is the stage they all stand on. Learn to see the pink-stained snow and the rust-coloured water for what they are, hold a living krill in your hand if a guide offers it, and you will carry home a far deeper understanding of how this dazzling ecosystem actually works — and why it is worth protecting. To keep exploring, follow the krill upward through our guides to the whales, the penguins, and the complete list of animals in Antarctica.
