Krill are small shrimp like crustaceans that live in the ocean.
Although small in size (measuring about 2 inches on average) they play a very important role in the regulation of our oceanic ecosystem and food chain.
Hundreds of animals and marine species (such as fish, squid, penguins and whales) rely on krill as a primary source of food and nutrients.
Without the existence of krill many animals (such as those in the Antarctic waters) would not survive.
Krill are often found traveling in large, dense masses commonly referred to as clouds or swarms.
These small invertebrates are a pinkish-red translucent color and when traveling in large enough groups will cause parts of the ocean to appear pink.
There are currently about 85 species of krill known to exist and they are broken down into two families: Euphausiidae and Bentheuphausia ampblyops.
Euphausiidae are found swimming closer to the surface of the ocean (which make them easier for biologist to study) while the lesser known primitive Bentheuphausia ampblyops are found living in deeper waters (below 3,000 feet).
Physical Characteristics and Appearance
The anatomy of krill can be broken down into three segments: the head, the thorax and the abdomen.
They have two antennae and several pairs of thoracic legs which vary depending on species.
The legs are broken down into three distinct functions which include swimming legs, feeding legs and grooming legs.
As they grow they develop a hard exoskeleton (transparent in most species) which is used to help them defend against attacks from predators.
As krill continues to grow they eventually outgrow their exoskeleton and go through a process known as moulting where they shed their exoskeleton in order to develop a new one.
Moulting may also occur when a krill shrinks in size which can happen in environments where there are large temperature fluctuations or when krill shrink due to a lack of sufficient food availability.
To assist with vision krill have compound eyes that allow them to observe more of their environment and help them detect fast moving objects.
This is especially important not only for locating food but also avoiding potential attacks from predators.
Aside from krill that belong to the Bentheuphausia amblyops family these aquatic animals are bio-luminescent and are capable of emitting light from their bodies.
Although the purpose of this is unknown it is speculated that generating light may play a role in mating, social structure and even self defense by providing a level of camouflage against their background, particularly when viewed from above where the sunlight shines down on them.
Depending on the species krill can grow anywhere from 0.4 inches to nearly 6 inches.
Self Defense
Krill are known to use several different methods to protect themselves against both smaller and larger predators.
As mentioned previously krill are known to develop a hard exoskeleton which makes it difficult for weaker prey to successfully attack, injure and kill them.
When being chased some krill have been observed shedding their exoskeleton as a decoy to distract their pursuer and lead them into believe the decoy is food.
Krill will also travel in large swarms with thousands of other krill and migrate to depths of 3,000 feet or more in order to protect themselves from being eaten.
The large swarms act as a form of defense and confusion among smaller prey that are likely to attack krill when they are traveling alone.
When traveling as a swarm krill are known to use vertical migrations to minimize their likelihood of being attacked.
As a group they will travel towards the surface of the water to feed and reproduce and will travel back to deeper waters together where it is safer and they are less likely to be attacked by animals that commonly hunt at or near the surface.
Unfortunately traveling in a swarm may make krill more susceptible to attacks from much larger predators that are known to hunt swarms of krill in order to feed themselves.
When attacked by whales, large fish or marine birds krill may end up dispersing and separating from one another to confuse their attacker and protect themselves in an every man for himself type of scenario.
Another less confirmed form of self defense of krill is to use their bio-luminescent abilities to help them blend in with their background.
While this may make sense and be a very effective self defense measure not enough is known about why they emit light to consider whether or not this has to do with self defense, communication or if it play a major role in a different area of the krill’s life.
Reproduction and Lifespan
Depending on the species and environment the mating season for krill can vary.
In order to fertilize the females eggs during mating periods the male krill will swim up to the female and deposit their sperm sack into the females genital opening.
Female krill can lay thousands of eggs seasonally and some species will either carry their eggs (which can take up to 1/3 their body mass) or drop them at which point they sink to the floor of the ocean leaving the baby krill to swim up on its own once it hatches.
The average lifespan of krill varies from 2 – 6 years although some (which survive being hunted) can live up to 10 years.
Diet
In terms of diet krill are known to eat phytoplankton (microscopic single-celled plants), copepods, zooplankton, algae and fish larvae.
Although most species are omnivorous (plant eaters) there are a few species that consume other animals such as fish larvae and zooplankton.
Some krill have even been observed eating other krill.
In order to obtain their food krill gather their food using a filter feeding method in which they filter their food from the water using their front legs.
The legs act like combs by allowing these animals to separate their food from the water that passes by.
As stated earlier krill are extremely important for feeding other marine animals.
In addition to being a food source krill also help break down other prey into forms of food that are otherwise unable to be digested by other animals.
Humans and Krill
Although not a common food for many people, krill has been harvested as a source of food for both humans and domestic animals, and sold as krill oil which some argue to be better than fish oil.
Studies have shown that the harvesting of krill can also carry with it toxic chemicals that are ingested by humans who eat krill and/or take krill oil.
When consumed by people the krill’s exoskeleton must first be removed as it contains toxic chemical that are poisonous to humans.
In the arctic krill are also known to play a role in carbon cycling by releasing feces when they migrate towards deeper waters after feeding and/or reproducing.
10 Interesting Krill Facts
1) There are currently over 80 known species of krill that have been recorded living in the ocean.
2) Most commercial krill hunting activities occur in the southern ocean.
3) The oldest known ancestors of krill have been recorded existing as far back as 130 million years.
4) Krill migrate vertically traveling towards the surface of the water during the night (to look for food) and back down into the ocean during the day (to avoid predators).
5) Krill are equipped with gills that allow them to extract oxygen from the water.
6) They are also cold-blooded allowing these small crustaceans to adjust to cold or freezing environments without the need for body fat or an increased metabolism to keep them warm.
7) Krill possess organs called photophores that allow them to emit light from their body. Possible reasons for this use may include communication and mating rituals.
8) These crustaceans have been hunted since the 19th century or earlier as a form of food for human consumption.
9) Since krill feed on plant life they are considered to be a herbivore species.
10) Because krill plays such an integral part of the diet of many marine animals without krill a number of marine mammals and fish could possibly become extinct.