Krill Facts & Worksheets

Krill are crustaceans that are an inch long and can be found in all the world’s oceans. It was named after the Norwegian word krill, which means “small fry of fish.” Krill are small, but their importance to the food chain is enormous.

See the fact file below for more information on Krill, or you can download our 29-page Krill worksheet pack to utilize within the classroom or home environment.

Key Facts & Information

TAXONOMY

• Euphausiacea is divided into two families: the Bentheuphausiidae, with only one species, and the Euphausiidae, with ten different genera and approximately 85 known species.
• Antarctic krill, Pacific krill, and Northern krill are the most well-known species.

ANATOMY

• Krill are crustaceans with a chitinous exoskeleton composed of three segments: the cephalon (head), thorax, and pleon (legs and tail). In other crustaceans, the first two segments are joined and referred to as the cephalothorax. 
• Krill have complex compound eyes. Some species use screening pigments to adapt to changing lighting conditions. 
• Krill have two antennae and several pairs of thoracic legs, known as thoracopods, due to their attachment to the thorax. Its number differs between genera and species. 
• Since krill are decapods, it has five pairs of swimming legs known as pleopods or “swimmerets.”
• Krill resemble shrimp in appearance but only grow to a maximum length of 2 inches and weigh less than one ounce. The externally visible gills of krill distinguish them from other crustaceans. Most krill species have a transparent outer shell.
• Krill are bioluminescent animals with light-emitting organs called photophores, except for the Bentheuphausia amblyops species. These photophores are complex organs that muscles can rotate with lenses and focusing abilities.

DISTRIBUTION

• Krill can be found in the world’s oceans, though not all species are found everywhere. Most species have an intercontinental distribution, and many have neritic distributions.
• Thysanoessa species can be found in the Atlantic and Pacific oceans, consisting of Pacific krill. Northern krill can be seen from the Arctic to the Mediterranean Sea.
• The four species of the genus Nyctiphanes have endemic distributions. They are prevalent along the upwelling areas of California, Humboldt, Benguela, and Canarias Current Systems, where most of the largest fisheries occur.
• Several species are known from the Antarctic, one from the genus Thysanoessa and six from the genus Euphausia. Antarctic krill (Euphausia Superba) typically live at depths of up to 100 meters, whereas Ice krill (E. crystallorophias) usually live at depths of 300 to 600 meters. Both can be found south, with Ice krill predominating in pack ice regions. Other species known to exist in the Antarctic Ocean include E. frigida, E. longirostris, E. triacantha, as well as E. vallentini.

LIFE STAGES

• Once krill hatch from their eggs, they undergo several larval stages: nauplius, pseudometanauplius, metanauplius, calyptopsis, and furcilia. 
• Nauplius. Despite their diverse forms, crustaceans are united by the nauplius, a special larval form.
• Pseudometanauplius. This stage is only found in species that lay eggs in an ovigerous sac (sac spawners). The larvae grow and molt several times, shedding their exoskeleton and starting to grow a new one. The larvae feed on yolk reserves within their bodies up to the metanauplius stage.
• Krill molt when it outgrows its rigid exoskeleton. Molting frequency varies between species and is influenced by external factors, such as latitude, temperature, and food sources.
• Calyptopsis. The stage where it develops a mouth and digestive tract and starts to feed on phytoplankton. The larvae should reach the photic zone (upper layers of the sea where phytoplankton thrive) by this time as their yolk reserves are depleted, and they would starve if not.
• Furcilia. Segments with sets of swimmerets are added beginning at the frontmost parts. 
• After the final stage, it evolves into the shape of an adult, in which it develops gonads (primary reproductive organs) and sexually matures.
• A few high-latitude krill species can live for more than six years, and others only for two years. The longevity of subtropical or tropical species is even shorter, which is only 6 to 8 months.

BEHAVIOR

• Most krill are swarming animals with varying sizes and densities based on species and location. Antarctic Krill swarms range from 10,000 to 30,000 individuals for every cubic meter. 
• Krill typically migrate vertically. They spend the day on deeper levels and rise to the surface at night. The deeper they go, the less active they become to avoid encounters with predators and conserve energy. During the day, some species form surface swarms for feeding and reproduction.
• Krill usually swim at a few centimeters per second (0.2 – 10 body lengths per second), propelled by their swimmerets. Their more extensive migrations are influenced by ocean currents. 

REPRODUCTION

• The mating season varies according to species and climate. During this time, the male releases a sperm sack at the female’s genital opening called thelycum.
• Females can carry thousands of eggs in their ovaries, representing up to one-third of their body weight.
• Krill can have multiple hatchlings in a single season, with interbreed intervals that can last days.
• Krill has two types of hatching process: “Broadcast spawners,” where the female releases the fertilized eggs into the ocean, where they sink, disperse and are on their own; and the “sac spawners,” in which the female holds the eggs tied to the backmost pairs of thoracopods until they hatch.

ECOLOGY

• Krill are an essential component of the aquatic food chain. Antarctic krill consume phytoplankton directly, turning the primary production energy into a suitable form for consumption by larger animals that cannot consume the relatively tiny phytoplankton directly but can consume krill. 
• Northern krill has a smaller feed intake basket and hunts for copepods and larger zooplankton.
• Krill is consumed by many animals, from small fish and penguins to large seals and baleen whales.
• Disturbances in an ecosystem that result in a decrease in the krill population can have far-reaching consequences. In 1998, during a coccolithophore bloom in the Bering Sea, krill could not feed, and its people in that region declined.
• This impacted other species: the shearwater population plummeted, which was believed to be why salmon did not return to the rivers of western Alaska that season.
• Aside from predators and food availability, other factors can influence krill mortality rates. Several parasites can infect various species of krill and cause mass mortality in affected populations. One such parasite is Oculophryxus bicaulis, discovered on the krill Stylocheiron affine and S. longicorne. It attaches itself to the animal’s eyestalk and sucks blood from its head.

USES

• Krill has been harvested as a food source since the 19th century. Though krill can be found all over the world, fishing in the Southern Oceans is preferred because the krill are much more “catchable”  and abundant.  
• Krill is a high source of protein and omega-3 fatty acids, developed as human food, dietary supplements such as oil capsules, livestock feed, and pet food. 
• Krill is most commonly consumed in Southeast Asia, fermented (with its shells intact) and finely ground to make a paste. The liquid produced during fermentation is also used to make fish sauce.
• The US Food and Drug Administration also issued a letter of no objection in 2011, allowing a manufactured krill oil product to be considered safe for human consumption.

Krill Worksheets

This fantastic bundle includes everything you need to know about Krill across 29 in-depth pages. These ready-to-use worksheets are perfect for teaching kids about the Krill, inch-long crustaceans found in all the world’s oceans.

Complete List of Included Worksheets

Below is a list of all the worksheets included in this document.

• Louis Pasteur Fact File
• The Life of Pasteur
• Career in Grid
• Crossword
• Pasteur’s Contributions
• Biogenesis vs. Abiogenesis
• Scientific Aptitude
• The Scientific Method
• A Well of Disease
• Mr. Perseverance
• Get Vaccinated!

Frequently Asked Questions

What is krill?

Krill are small, shrimp-like creatures that live in the ocean. They are a type of plankton, which means they are tiny organisms that float in the water and are an important food source for many larger animals.

What do krill eat?

Krill eat small plants and animals that live in the ocean, such as phytoplankton and zooplankton. They also eat small pieces of dead plants and animals that have fallen to the ocean floor.

What animals eat krill?

Many animals eat krill, including whales, dolphins, seals, penguins, and seabirds. They are also an important food source for fish such as salmon and cod.

Where do krill live?

Krill live in the ocean, mostly in the colder waters of the Antarctic and Arctic. They can be found in the open ocean as well as in coastal areas.

Why are krill important?

Krill are important because they are a key part of the ocean’s food web. They provide food for many larger animals and help to keep the population of these animals in balance. Krill also play an important role in the ocean’s ecosystem by helping to recycle nutrients and by serving as a food source for other organisms, including fish that people depend on for food.

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