Krill are tiny shrimp-like, semi-transparent crustaceans measuring about one inch long and weighing a fraction of an ounce. They are in the same class as crayfish, lobsters, woodlice, shrimp, and crabs.

Moreover, we have over 85 skill species, including Antarctic and Northern krill. They all are pelagic, meaning they live in the open sea and congregate in amazingly huge swarms. In most cases, the swarms are more than 10,000 individuals per cubic meter.

Another interesting fact about krill is that they are plankton. The term ‘plankton’ refers to organisms that cannot swim against currents and tides because of their size, weakness, or immobility. In other words, they are tiny creatures in a state of drift, earning them the unofficial name of drifters. Krill are too small and weak to swim. However, like other phytoplankton and zooplankton (two types of plankton), these animals occupy a special place in the global food chain.

If you are interested in learning more about this fascinating zooplankton, read on.

Dried krill
Dried krill


Like other crustaceans, krill are covered in an external skeleton that supports and protects its body, known as an exoskeleton. At the same time, they have two main body parts. The first one is the cephalothorax, composed of the fused thorax and head. The next one is the pleon (abdomen). If you choose, add the tail fan to increase the body parts from two to three.

Adult krill
Adult krill

The external skeleton is transparent in most krill species.

Compound eyes are another conspicuous feature of this zooplankton. You can also find species with a screening pigment, which helps them adapt to different lighting conditions.

Krill also have two antennae and plenty of thoracic legs. As the name suggests, all these features are attached to the thorax. The exact number of these legs varies depending on the species and genera. However, since these sea animals are decapods, they have ten swimming legs that look the same as those of freshwater crayfish or lobster.

Some adult krill measure between 0.4 inches and 0.8 inches. However, some species can grow to up to 5.9 inches.

While krill look like other crustaceans like shrimp, they have one unique feature: externally visible gills for taking in oxygen.


Most krill are renowned filter feeders able to use their thoracopods to filter out the right food types from the water.

Two deep sea krill
The green part behind the head is captured phytoplankton

Some of these zooplankton feed on phytoplankton. Others are omnivorous, meaning they can survive on both plants and animals. There are also predatory krill species. They prey mainly on larvae and zooplankton.


Krill are found worldwide, but different species are predominant in different oceans or parts of the sea. For example, the Antarctic krill is dominant in the Southern Ocean. Estimates show that it makes up a biomass of approximately 379,000,000 tones in this area.

Since krill are plankton, they depend on currents and tides to move. So, their population in different parts of the ocean always changes depending on the direction of these forces.


These sea animals’ breeding seasons vary depending on species, climate, and location.

When a male is ready to reproduce, it deposits sperm near the genitals of the female. That’s enough to assist the female in laying fertilized eggs throughout the breeding season.

Some krill species release the eggs into the water, but others carry them safely in their specialized sacs until the gestation period is over.


Krill are a critical link in the ocean’s food chain. It connects phytoplankton at the bottom of the chain to larger predators at the top.

Small animals like penguins and fish and large ones like baleen whales feed on the crustaceans. 

Since most animals depend on krill for food, a minor disturbance in their abundance can harm the entire ecosystem.

Krill are not endangered, but over-dependence on them could lead to severe problems in the future. 

Climate change and marine pollution threaten these animals. The fact that they are caught frequently in some fisheries worldwide is another potential threat. Currently, krill is an essential food source in the Philippines, Spain, Japan, Russia, and other places.

Some studies show that the krill population has dropped by at least 80% since the 1970s due to these factors.

Facts about Krill

  1. Krill travel together in swarms of more than 10,000 individuals per cubic meter in water for protection. Some swarms are so large that you can see them on satellite images.
  2. Krill float along ocean currents and waves because they are too small and weak to swim.
  3. There are over 85 species of krill, and each of them has a few unique features.
  4. Krill’s population has dropped by about 80% since the 1970s because of overfishing, disease, and climate change.
  5. Krill oil contains omega-3 fatty acids and high levels of proteins. Experts believe that these fatty acids can reduce the risk of cardiovascular disease.


What is the role of krill in the food chain?

The role of krill in the food chain is to provide food for many oceanic life forms. They feed on phytoplankton, a type of plankton, but drift near the ocean’s surface to get enough sunlight and carbon dioxide. These single-celled plants use these things to make their food.
Krill are the primary food source for baleen whales, birds, fish, and many other living things.

Can humans eat krill?

Yes, humans eat krill in many parts of the world. Most people consider them the best source of proteins, Omega-3 fatty acids, vitamin A, and other valuable nutrients. Due to the increased harvesting of krill for human consumption and pollution-related activities, their population has dropped by about 80% since the 1970s. However, these sea animals are not considered as threatened as of today.

Is krill a fish or shrimp?

Krill is a fish, not a shrimp. These sea animals look like shrimp, but they have externally visible gills for taking in air that sets them apart.
Note that krill and shrimp are crustaceans, and that’s why they look alike. Also, remember that the number of people who feed on shrimp seems higher than krill.

Are krill intelligent?

If you observe krill over a short time, you’ll notice that they are intelligent. They know their strengths and weakness and can take advantage of that to survive for up to 10 years. Krill travel together in swarms of more than 10,000 individuals per cubic meter for protection. This behavior inspired the computer program for devising better traffic control systems known as the krill herd algorithm.

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