Krill – Tiny and important | Polarjournal
Nothing works in the Antarctic without krill: the small crustacean is the basis of the food chain there. No wonder that the sea turns red when a swarm is on the way. (Photo: Wikipedia)

We are lucky – the dreaded Drake Passage between Tierra del Fuego and the Antarctic Peninsula lies almost motionless in front of us. Hardly a breath of wind may bring forth even the trace of a wave, where otherwise storms rage and rising seas are the normal state of affairs. The sun shines flawlessly from a subpolar sky, and had it not been for the sudden appearance of a huge, reddish shimmering spot on the surface of the water – it could have been an almost uneventful crossing.

The biologists on board the expedition ship heading for Antarctica immediately realize what is causing the reddish area on the sea surface – krill, and in great quantities! Millions of these 6-centimetre-long luminescent shrimps colour the sea… A large krill swarm that has already covered an area of 450 square kilometres (after all, half of the canton of Schwyz, or the area of Andorra or the Seychelles) naturally does not remain hidden from the “consumers” for long. Misjudged as an hors d’œuvre, the luminous shrimp in large swarms is the main food of many whales, seals, fish, birds and squid around Antarctica.

And already the humpback whale shows up! First, its huge mouth breaks through the glassy sea. It’s grooved like the corrugated metal of a garage door – only twice as big. Then the mighty, heavy whale body shoots up to half its length out of the hitherto unmoving blue sea.

Sinking back, the humpback whale closes its oversized mouth almost in slow motion, and like waterfalls, the squeezed seawater runs out of the corners of its mouth as the whale’s body sinks completely back into the water of Drake Passage. Before it submerges completely, its bulging mouth with the widely spread furrows remains visible for a short time – away! The last curls of water calm down, the Southern Ocean lies again as still and unmoving in front of the ship’s bow as before.

Two humpback whales feeding. With their big mouths they sift the krill out of the water by the ton. (Photo: Archive)

Basis of the food chain

The passengers of this Antarctic ship have just witnessed how the food chain in the Souther Ocean works. Antarctic krill (Euphausia superba) occupy a central position in the food web around Antarctica. For example, it is the daily standard diet for all seven baleen whale species found there. A blue whale consumes about four tons of krill per day, which makes three to four million individual krill crustaceans. According to a scientific study, all baleen whales together consume between 1.6 million and 2.7 million tons of krill every summer season in the South Atlantic sector of the Southern Ocean alone. If one adds up the krill consumption of all baleen whales of the entire Southern Ocean, it adds aup to an estimated 34 to 43 million tons per year – before the strong decline of the whales through whaling, it is supposed to have been even 190 million tons.

Besides whales, other marine mammals are also dependent on krill, especially the crabeater seal, whose name already gives away its favourite food. Because this Antarctic seal is said to be the second most abundant mammal after humans, the amount of krill consumed is also enormous. Although estimates vary widely, crabeater seals far outnumber the seven baleen whale species in the South Atlantic portion of Antarctica: they are said to consume 50 to 130 million tons of krill annually – at least equal to three times more than the whales claim for themselves!

But penguins are also krill lovers; almost all species eat krill in varying amounts. However, krill plays a prominent role for emperor, Adélie, bridled, gentoo, macaroni and rockhopper penguins. While a penguin normally needs at most one kilogram of krill per day, an example of extreme gluttony has been published from the Ross Sea: an Adélie penguin was caught there with 4200 krill crabs in its stomach, which can add up to more than four kilograms in weight…

Thanks to research, we know that the many millions of chinstrap penguins living on the South Sandwich Islands alone (a good three quarters of the world’s population) eat 4000 tons of krill per day, which is the “equivalent” of about 3.6 billion individual krill crustaceans. On one island of the South Orkney Islands, too, the five million Adélie penguins have been looked at closely and calculated – they need up to 9000 tons of krill and fish larvae in one season to raise their chicks.

Such examples may suffice to demonstrate the importance of the position of krill within the South polar food chain, particularly the species Euphausia superba, the Antarctic krill. Its enormous biomass is of outstanding importance for the marine ecosystem of the Southern Ocean. The immense shoals, which include two species of krill in particular from the Southern Ocean, are the largest aggregations of marine life.

In particularly dense swarms, called super swarms, between 10,000 and 30,000 individual crustaceans can be counted per cubic meter of water. So if krill is so common – how many tons of it are there in total in this world? – Between 60 million and 155 million tons are said to be found, an estimate based on recent acoustic measurements. According to the fishing industry, which has shown an ever-increasing interest in krill fishing since the 1960s, there are said to be 400 to 500 million tonnes of krill in the world’s oceans. In short, no one knows for sure how much krill is wriggling around in the Southern Ocean.

Freshly caught and predigested: a gentoo penguin feeds its young with a huge portion of krill. (Image: Heiner Kubny)

Descend and ascend again

Strictly systematically, krill belong to the class of crustaceans, within which they belong to the higher crustaceans (Malacostraca). Among them are the decapods (Decapoda) and the luminous crustaceans, the krill, which is a small crustacean and resembles shrimps. Krill have special organs on their eyes and trunk that can produce a bluish-green light thanks to bioluminescence. Worldwide there are about 90 species of krill, which differ greatly in size. The smallest are only a few millimetres long, the largest deep-sea species reach a body length of 15 cm. As a species of the offshore, open seas, krill follows a so-called pelagic way of life and belongs to the zooplankton.

Although Antarctic krill (Euphausia superba) in particular is probably one of the best-documented pelagic species, there remains great uncertainty about certain key roles of its lifestyle. It is also unclear what the driving forces are behind its enormous abundance and wide distribution (with some core areas of particularly high density) over a good 36 million square kilometres of ocean around Antarctica.

In any case, a juvenile krill begins its life as a larva: fertilized females deposit between 1600 and 4000 eggs in the water for up to ten hours during the Antarctic summer and promote the sinking of their eggs by vigorous thrusts with their thoraic legs. Soon the nauplius larvae develop from the eggs in different water depths up to a maximum of approximately 3000 m under the sea surface, which begin to rise again and reach the water surface well one month after spawning. Here the little one continues to grow, and every two to three weeks, it gets too tight for the young krill in its chitinous shell: it sheds its skin regularly. And if not eaten first, it can grow to 6 centimetres tall and live five to six years.

An extraordinary discovery was made by researchers from the British Antarctic Survey (BAS) and the National Oceanography Centre in Southampton. They, or rather their remotely operated underwater vehicle, encountered adult krill, including females in the spawning stage, at a depth of 3000 m off the Antarctic Peninsula. Until now, it had been assumed that krill – once grown up – would only live in the top 150 metres of the sea.

Small and light: a few dozen krill crabs. (Photo: Simon Wright, BAS)

“Grazing” under the ice

And what if the sea freezes over in the Southern winter? The more sea ice, the better for the krill community! Meanwhile, research has shown that the duration and extent of sea ice influence egg-spawning. Good winter sea ice conditions lead to early reproduction. This then also guarantees successful spawning in the summer.

Good ice winters in the area of the Antarctic Peninsula, where the most important spawning and nursery areas of Antarctic krill are found, therefore not only influence krill density in that zone, but also include regions far north of the winter ice, such as the waters around South Georgia.

Research by the German research vessel Polarstern has made it clear that krill gather under ice floes in early winter, when the Southern Ocean freezes over rapidly. Microalgae begin to grow on the rough, jagged, uneven underside of the sea ice, covering large areas. While above, in the truly fresh air, everything is frozen stiff and at most a few emperor penguins waddle across the ice between the breeding colony and the water’s edge, the swarms of krill under the ice cover must feel like they are in a gourmet paradise: They graze on the algae. A single krill, its stomach rumbling, can nibble a sheet of ice the size of a piece of letter paper clean in a good twenty minutes. If danger is imminent, the krill hide in the cracks and crevices of the ice.

A young krill “grazing”. In 20 minutes it eats the algae from the ice on the surface of an A4 sheet. (Photo: Hauke Flores)

Danger due to heating

It is not yet clear to the researchers how krill survive the Antarctic winter, especially since it obviously cannot store energy in the form of fat and the algal turf under the ice is not always formed in the same way everywhere. It is known that the metabolism is reduced to a necessary minimum. It has also been found in the laboratory that Antarctic krill can survive up to 200 days without food. But it only does this because the animal shrinks and begins to consume its own body; all this to keep the metabolism going.

No ice, no krill in the Southern Ocean! And that would have devastating consequences for the food chain, in which so many animal groups are involved. Concerned voices point out that it is precisely the Antarctic Peninsula that is warming up even more than the rest of the White Continent in the course of global climate change. The signs are clear: in the last fifty years, the air temperature in the peninsula region has risen by 2.5°C – a record increase by global standards! The number of frost-free days (with temperatures above 0°C) has increased by three quarters, UV-B radiation has increased, the water is getting warmer, and in the same period almost 90 per cent of all glaciers on the peninsula have retreated.

According to the British Antarctic Survey (BAS) the ice shelves are not faring any better: seven of these ice sheets, up to a kilometre thick, have been affected by heat and are disintegrating on the Antarctic Peninsula alone (e.g. Larsen and Wilkins ice shelves). Projections indicate that the area of sea ice will continue to decrease by about 250,000 square kilometres per decade.

This development has not left krill unscathed. However, it is not certain whether the 80 percent decline in krill stocks since the mid-1970s in the southwestern Atlantic, where more than half of Antarctic krill occur, is solely due to climatic warming. However, species that feed on krill are already reacting to the meager food supply – their populations are dwindling.

Krill stocks are increasingly targeted. No one knows how much food people are taking away from the animals. “Skyfrost”, the reefer container registered in Greece, next to the Russian reefer vessel “Pamyat Ilicha” in Discovery Bay, Antarctica. (Photo: Paul Hilton / Greenpeace)

Krill hunting with fishing vessels

At this point, of all places, the fishing fleet of the krill industry appears on the darkening horizon. At a time when the climate is changing, the ice is melting, researchers are still puzzling over important connections in the life of krill, and krill populations have declined, people are getting a craving for krill.

Interest in krill fishing began in the early 1960s, when fishing nations such as the then Soviet Union developed a serious interest in krill fishing in the Antarctic. The scientific figures sounded tempting: because the hundreds of thousands of seals and whales that had been slaughtered there since the discovery of Antarctica and until the 1960s were no longer eating krill, there was supposed to be a surplus of 150 million tons of krill.

The assumption that this amount – because it was no longer consumed by anyone – would simply rot away somehow was all too simplistic. But the calculation example alone was enough to make the catching nations believe in an almost inexhaustible potential.

In addition, at the end of the seventies, the 200-mile zone was introduced as the territory of the respective coastal countries. Not so in Antarctica, whose international waters knew no such zone – and with their abundance of krill were therefore a welcome alternative.

After an initial phase, the commercial exploitation of Antarctic krill stocks began in 1973 and expanded rapidly, reaching its first peak in 1982 at 530,000 tonnes, and has since been the largest component of the Southern Ocean fishery, despite the current reduction in catches. The fishing season lasts from 1 December to 30 November.

While the average catch of krill for the years 2004 to 2013 was around 156,000 tonnes per year, the yield for 2019 alone rose to over 380,000 tonnes, according to a report on global fisheries by the United Nations Food and Agriculture Organization (FAO). These are the highest catches since the early 1990s. They are scored by a good dozen fishing vessels. The maximum possible annual catch in the South Atlantic sector of the Southern Ocean alone has been set at 620,000 tonnes.

In the spring of 2020, Russia let the world know that it would soon be sending its own fishing vessels to catch krill in Antarctica again – for a good ten years, the giant country has left the Antarctic fishing grounds to other nations and stopped fishing. This is now to change again.

In response to rising catches, the Association for Responsible Krill Fisheries (ARK) declared a number of nearshore marine areas on the Antarctic Peninsula closed zones in 2018, mainly near significant penguin colonies.

Krill products are becoming increasingly important for humans: among other things as fish food (left) or as a rich oil for dietary supplementation (right). (Photo: Archive)

Variety of krill products

Meanwhile, krill has been shown to be high in protein and fats. Above all, it is very rich in certain omega-3 polyunsaturated fatty acids, which are important for metabolism, cardiovascular functions, bones, joints and brain. Although these essential fatty acids are also found in algae oils and in fruit, the krill industry is vigorously promoting krill oil for human health.

For example, the number of krill oil patents for pharmaceutical products and food supplements has risen sharply in recent years. At the moment, however, frozen krill tail meat is the main product for human consumption.

Krill is also processed for pharmaceutical and industrial applications. Chitin and chitosan are produced from its shells (for foams, medical products, fibres, foils, toothpaste, paper production, etc.). Krill enzymes help restorers restore works of art.

However, an even bigger market is greedily waiting for the krill products: Fish farms, of which there are more and more worldwide, need food. The use of krill as feed in so-called aquacultures seems to stimulate investment in krill fisheries because salmon farms in particular lack sufficient food for their fish.

Now we inevitably enter an area that reveals the horrendous waste of resources in today’s fish consumption: Already every second fish that ends up on a plate comes from a fish farm (mostly from Asia). It is therefore not surprising that the fish farming industry consumes almost the entire world production of fish oil and over half of fish meal as feed.

Confusingly similar: The Norwegian krill (Meganyctphanes norvegica). The word krill comes from Norwegian and means whale food. (Photo: Wikimedia)

Krill catch increases

The amount of food needed worldwide is increasing, but the efficiency remains poor: it takes 20 kilograms of fish feed to produce 1 kilogram of fish… The alternative of krill comes in handy in times of shrinking supply, as the fishing industry struggles with stagnating catches. Krill is considered a high quality, attractive energy food because of its abundance of protein and amino acids. Its pigments give farmed salmon an appetising colour, and its low toxin content makes krill stand out from conventional fish products.

So the demand for krill products is growing rapidly. This, coupled with the fact that the northern hemisphere krill fishery is facing regulatory restrictions, lets the industry focus its interest on the Southern Ocean krill stocks around Antarctica. There the pressure on these crustaceans – nota bene a foundation of the local food chain – will increase within a short time.

But problems have been looming for some time. Thus, krill fishing regions largely overlap with the breeding and feeding areas of penguins and seals, because fishing vessels are mainly active in coastal areas. Moreover, no one knows how much krill actually occurs in the Southern Ocean – stock estimates are too imprecise. How much krill do whales, penguins & Co. actually need to survive? And to what extent do inflows and outflows of krill influence stock numbers in individual fishing areas?

Dispute over regulations

In 1982, the “Convention on the Conservation of Antarctic Marine Living Resources” was established under the Antarctic Treaty (CCAMLR / Convention on the Conservation of Antarctic Marine Living Resources). This agreement seeks to balance conservation and protection of marine species with krill fishing. CCAMLR is the first international fisheries agreement to incorporate ecosystem and precautionary approaches.

The key position of krill in the Antarctic ecosystem plays a major role in the formulation of the basic principles of CCAMLR. Despite a progressive approach, this agreement is facing growing criticism, for example because the fishing quotas apply to huge areas, but the catches themselves ultimately take place on only about one fifth of these areas.

Several fishing nations continue to resist refining quota/area allocations despite evidence that current practices negatively impact krill predators such as penguins and fish. There is a lack of adequate monitoring of fishing vessels, and different conversion factors from the processed catch back to the original weight could make the quantities actually reported appear four times smaller than what was actually taken from the sea.

Antarctic krill, the small luminescent shrimp from the vastness of the Southern Ocean, has captured the imagination of biologists, politicians and industrialists alike like no other animal in this part of the world. It is to be hoped that greater weight will be attached to the idea of protection than to the greed for profit. Nothing would be worse than to deprive the whales, seals and penguins of Antarctic food.

The Krill-eaters

Important animal species directly dependent on krill as a food source


  • Seabirds generally consume large amounts of krill. Adélie penguins alone consume over four-fifths of all krill consumed by seabirds in Antarctica.
  • Penguins: Emperor Penguin, Adélie Penguin, Chinstrap Penguin, Macaroni Penguin, Gentoo Penguin, Rockhopper Penguin.
  • Albatrosses: Black-browed Albatross, light-mantled Sooty Albatross, Grey-headed Albatross.
  • Storm birds: Southern Giant petrel, Northern Giant petrel, Antarctic petrel, Cape petrel, Snow petrel, Shearwater (several species), White-chinned petrel.
  • Petrels and prions


  • Seals: With the exception of the Southern elephant seal, all Antarctic seals eat krill to some extent. Crab-eating seal, leopard seal, Weddell seal, Ross seal, fur seal
  • Whales: Minke whale, blue whale, fin whale, sei whale, humpback whale


  • fish and squid/ squid. Some species of fish and squid in the Southern Ocean live on krill. Exact data on the population of squid are lacking, but it is assumed that this group of animals also feeds on other organisms.

By Peter Balwin (text)

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