Adélie penguins standing together on Antarctic sea ice

Chapter 2 · Grades 4–6

Life on the ice

Antarctica may look empty, but its ocean is busy with life. Tiny drifting plants help feed some of the biggest animals on Earth.

Adélie penguins · WindWalker Antarctic photo archive

Where life gathers

Most Antarctic animals find their food in the Southern Ocean.

The icy land is difficult for plants and animals. The ocean, however, carries nutrients and supports a huge food web. Penguins and seals may rest or raise young on land and ice, but they hunt in the sea.

Follow the energy

The krill connection

Krill are the small but mighty link between tiny ocean plants and many Antarctic animals. The arrows mean “is eaten by.”

Phytoplankton Tiny plant-like drifters use sunlight

Antarctic krill The food web’s central link

Penguins & fish Many species eat krill

Leopard seals & orcas These hunters may eat penguins

This is one path through a much bigger web. Krill also feed fish, squid, flying seabirds, some seals, and enormous baleen whales. Many seals eat krill, fish, or squid directly; leopard seals are the seal species best known for hunting penguins.

Adélie penguins standing on sea ice — Penguins depend on a healthy ocean food web.

A leopard seal resting on sea ice — Leopard seals can hunt penguins and other seals.

Antarctic fur seals swimming together in deep blue water — Antarctic fur seals mainly eat krill, fish, and squid.

Small animal, giant job

Meet Antarctic krill

An adult Antarctic krill is about 6 centimetres long—roughly the length of a child’s little finger. Krill gather in enormous swarms and eat phytoplankton. Fish, squid, seabirds, penguins, seals, and baleen whales all eat krill.

Because so much of the food web passes through them, scientists sometimes call krill a keystone species. Imagine the centre piece in an arch: many other pieces rely on it.

A translucent Antarctic krill feeding beneath blue winter sea ice — A real Antarctic krill feeding under winter sea ice. Krill may be little, but they gather into enormous underwater clouds. Photo: Dr Wayne Trivelpiece, NOAA NMFS/SWFSC AMLR Program.

Wild neighbours

Typical Antarctic animals

These animals have body parts and behaviours—called adaptations—that help them survive cold water, wind, and ice.

Penguins

Dense, waterproof feathers trap warmth. Emperor penguins huddle; Adélie, chinstrap, and gentoo penguins build colonies near the coast.

Visit the penguin gallery →

Seals

A thick layer of fat called blubber holds in heat. Weddell, crabeater, leopard, fur, and elephant seals live in the Antarctic region.

Visit the seal gallery →

An adult albatross beside a fluffy chick on a grassy, rocky slope

Flying seabirds

Albatrosses, petrels, skuas, and terns travel over the Southern Ocean. Long wings help some glide great distances while searching for food.

Visit the bird gallery →

Several chinstrap penguin chicks covered in thick gray down among adult penguins — Chinstrap chicks still wearing soft, non-waterproof down.

An adult chinstrap penguin with worn feathers lifting away during its annual moult — An adult chinstrap penguin undergoing its annual catastrophic moult.

A bird that “flies” underwater

Is a penguin really a bird?

Yes! Flying does not make an animal a bird—feathers do. Penguins also have beaks, lay eggs, and are warm-blooded.

Wings became flippers

A penguin’s short, stiff wings cannot lift it through air. Instead, they push against water, almost as if the penguin is flying through the ocean.

Fluffy down comes first

Chicks begin with soft down that traps warmth but is not waterproof. Before going to sea, they replace it with short, overlapping waterproof feathers. This first change is called fledging.

Adults change coats too

Once each year, an adult replaces all its worn feathers in a fast “catastrophic moult.” It must stay out of the sea and cannot hunt until its waterproof coat is ready.

Two different coat changes: a chick fledges once, replacing its down with its first waterproof feathers. An adult moults every year, replacing one complete waterproof feather coat with another.

A southern elephant seal resting on a stony beach beside the ocean — On land an elephant seal looks slow; underwater its smooth body becomes a powerful diving machine.

A mammal made for the sea

Is a seal really a mammal?

Yes! Seals breathe air with lungs, are warm-blooded, give birth to live pups, and mothers feed their pups milk.

Do seals have legs?

They have four limbs, but evolution reshaped them into flippers. The bones are still inside. Flippers steer and propel a seal far better than ordinary legs could.

How can they stay underwater?

A seal breathes at the surface and holds its breath below. Extra blood and oxygen-carrying proteins store oxygen in its blood and muscles, where it can be used slowly during a dive.

They must return to air

Seals do not have gills. Weddell seals even keep breathing holes open in winter ice with their teeth, then navigate back to those holes in the dark.

2,360 ftA Weddell seal can reach about 720 m and remain underwater for up to 45 minutes.

1.2 milesA southern elephant seal can reach about 2 km and hold its breath for up to 2 hours.

Built for cold

Feathers and fur can trap pockets of warm air. Blubber works like a thick, built-in winter coat. Huddling lets penguins share warmth. Even krill have a winter trick: when food is scarce, they can shrink and use less energy.

Science sources

This chapter was checked against educational material from the Australian Antarctic Program.