Scientists Say: Krill | Science News for Students

Scientists Say: Krill

These tiny critters play a big role in the ocean
Jul 16, 2018 — 6:30 am EST

This Northern krill is a tiny crustacean that swims in the ocean.

Øystein Paulsen/Wikimedia Commons/(cc-BY-SA 3.0)

Krill (noun, “KRIL”)

These are small crustaceans. They’re hard-shelled ocean-dwelling animals that are relatives of lobsters, crabs and shrimp. Krill feed on phytoplankton — tiny algae that make energy from sunlight. In turn, krill are dinner for whales, seals, penguins, squid and fish.

What krill lack in size, they make up for in numbers. For example, a single Antarctic krill (Euphausia superba) is only around 6 centimeters (2.4 inches) long. But these krill live in huge swarms — so huge that scientists think there might be 500 million metric tons of Antarctic krill in the sea.  That’s equivalent to the weight of some 5 million blue whales (which, by the way, dine on krill).

In a sentence

Swarms of krill move so much water when they swim that they help to stir up nutrients in the ocean.

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Power Words

(more about Power Words)

algae     Single-celled organisms, once considered plants (they aren’t). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.

crustaceans     Hard-shelled water-dwelling animals including lobsters, crabs and shrimp.

krill     Tiny shrimplike crustaceans that live in the ocean and are the main food source of some whales.

nutrient     A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

penguin     flightless black-and-white bird native to the far Southern Hemisphere, especially Antarctica and its nearby islands.

phytoplankton     Sometimes referred to as microalgae, these are microscopic plants and plant-like organisms that live in the ocean. Most float and reside in regions where sunlight filters down. Much like land-based plants, these organisms contain chlorophyll. They also require sunlight to live and grow. Phytoplankton serve as a base of the oceanic food web.

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

squid     A member of the cephalopod family (which also contains octopuses and cuttlefish). These predatory animals, which are not fish, contain eight arms, no bones, two tentacles that catch food and a defined head. The animal breathes through gills. It swims by expelling jets of water from beneath its head and then waving finlike tissue that is part of its mantle, a muscular organ. Like an octopus, it may mask its presence by releasing a cloud of “ink.”

swarm     A large number of animals that have amassed and now move together. People sometimes use the term to refer to huge numbers of honeybees leaving a hive.

whale     A common, but fairly imprecise, term for a class of large mammals that lives in the ocean. This group includes dolphins and porpoises.