Antarctic krill

Antarctic krill are tiny shrimp-like animals that live in the cold Southern Ocean all around Antarctica. Each one is only about six centimetres long — roughly the size of your little finger — but together they are one of the most important animals on the whole planet.

Krill almost never swim alone. They gather in enormous groups called swarms, so crowded that thousands of krill can pack into a single bucket of seawater. From above, a big swarm can turn the sea a pinkish colour. Swimming in a crowd helps keep each krill a little safer from hungry mouths.

For their food, krill sweep up drifting specks of plant-like life called phytoplankton that grow near the sunlit surface and under the sea ice. In this way krill turn sunshine, caught by those tiny plants, into food that much bigger animals can eat.

And so many bigger animals do eat them. Whales, seals, penguins, fish and seabirds all feast on krill. Great baleen whales gulp huge mouthfuls and strain the water out through a comb-like sieve, keeping only the krill. Scientists call krill a "keystone" animal because so much of Antarctic life leans on them.

Because there are so many billions of them, Antarctic krill are listed as Least Concern, meaning they are not in danger right now. Even so, they need cold seas and sea ice to thrive, so keeping the ocean healthy and cool matters for krill — and for every animal that depends on them.