Family Euphausiidae, Bentheuphausiidae
Genera Euphausia, Meganyctiphanes, Nematobrachion, Nematoscelis, Nyctiphanes, Pseudeuphausia, Stylocheiron, Tessarabrachion, Thysanoessa, Thysanopoda, Bentheuphausia
Species 85 species
Krill is a group of 85 shrimp-like crustaceans that may be found in all the world’s seas. Despite their tiny size, krill play a vital role in the food chain, supplying food for hundreds of other species that eat them directly. Large baleen whales, such as the blue whale, fall into this category.
The name krill is Norwegian in origin, and it refers to 86 species of tiny shrimp-like arthropods belonging to the families Euphausiidae (9 genera) and Bentheuphausiidae (1 genus).
Krill is little decapod crustaceans that look like shrimp. They have a rigid, chitinous exoskeleton, like other crustaceans. Their bodies, like other decapods, may be divided into three pieces. The cephalothorax is made up of a fusion of the animal’s head and thorax. The pleon is the penultimate portion, which contains the 10 swimming legs as well as the tail fin, which assists in swimming. The exoskeleton of most species is transparent, enabling parts of the creatures’ organs to be seen in real time.
They also feature two antennae and a pair of thoracic legs known as thoracopods, as well as spherical, black compound eyes visible on the front of their heads. Unlike the pleon segment’s swimming legs, the thoracic segment’s legs contain some for eating and others for grooming. They resemble little crayfish, lobsters, or shrimp in appearance, but they only reach a maximum length of two inches and a weight of less than one ounce. Krill, unlike actual shrimp, have externally visible gills.
Habitat and Distribution
Although krill may be found in all the world’s seas, not all species have a worldwide distribution. Many species may be found in shallow waters in the photic zone, feeding on phytoplankton. The majority of species migrate from deeper waters during the day, where they may hide from predators, to shallower waters at night, when they can reach the species on which they feed while still in the dark.
Many krill species, utilise their most front thoracic legs to create a comb-like structure that filters food from the water surrounding them. These filters are very selective for many species, catching mostly diatoms and other unicellular phytoplankton. Other species are omnivorous, feeding on a variety of phytoplankton types as well as zooplankton. Other krill species are carnivorous, feeding only on planktonic animals like larval fish and copepods.
Krill are crucial species in the global food chain because they are one of the key means by which the energy stored in algae is transferred to the rest of the food chain, namely bigger animals that would otherwise be unable to consume tiny algae. Krill are generally numerous and schools together, making it possible to catch many of them at once. This has made them an important element of the diet of baleen whales, who are among the world’s biggest creatures. Penguins, seals, a variety of fish species, and others will eat krill directly.
Krill Life Cycle
Most krill species will go through five larval stages once a new egg hatches. The larvae are fed by the yolk reserves in their bodies throughout the first three stages. A mouth and digestive system will have evolved by the later stages, and they will begin to feed on phytoplankton. The larvae must have reached the photic zone at this point, which is the part of the ocean where light reaches and phytoplankton blooms. They, like other crustaceans, will moult many times throughout their development, replacing their exoskeleton as they outgrow it.
Most krill species mate by depositing a sperm sac on the thelycum of the female. During one breeding season, females may carry thousands of eggs and produce many broods. Some species, such as those in the genera Bentheuphausia, Euphausia, Meganyctiphanes, Thysanoessa, and Thysanopoda, will “broadcast spawn,” releasing their eggs freely into the water once fertilised.
Females of other species, known as’ sac spawners, ‘carry the eggs around with them. They are linked to the backmost pair of thoracic legs until matenauplii, the third of five normal krill larval stages, hatches.
Some krill species, such as Euphasia superba, which reside at higher latitudes, may survive for more than six years, but most tropical species only live for two years or less. They typically reproduce during their initial breeding season, which generally falls during the summer.
The majority of krill species do not get any specific conservation protection. They are, however, unquestionably a key component of global food chains, and their complex ecology must be carefully studied in areas where pollution is prevalent or where the effects of global climate change are now greatest. For example, algal blooms caused by pollution may have an influence on the whole food chain.
If these blooms change the nature of the phytoplankton population where they occur, krill, which eat a variety of algae, may have fewer options for food. If the krill population decreases, many other creatures higher up the food chain would suffer as well. In Norway, incidents like this have been linked to salmon failure to spawn, most likely owing to a shortage of food in these areas.
Fun Facts about Krill!
Hundreds of different species rely on krill for their food. This includes the blue whale, the world’s biggest living creature. This is only one intriguing and crucial feature of this species.
Truly Fish Food
Krill are not only an important food source for hundreds of other species in the wild, but they are also commercially exploited. Every year, 150,000-200,000 tonnes of krill, a tiny mammal weighing less than 0.07 ounces, are harvested across the world. People drink this in nations such as Spain, Japan, Russia, and the Philippines. In Japan, they are known as okiami, while in Spain, they are known as camarones, which is a generic term for shrimp.
However, the majority of this commercial catch is utilised as fish feed in commercial aquaculture operations and home aquariums, rather than being eaten by people. The krill are dried and packed before being fed to captive fish, as is common in the wild.
A Primary Consumer
Krill species represent a basic trophic level and are considered a key element of the food chain. They eat phytoplankton, which are primary producers who convert solar energy into organic matter. As a result, they are primary consumers—animals that eat plants and so make their energy accessible to the remainder of the food chain. Many bigger creatures, such as baleen whales, use krill as their primary source of food.
The Antarctic Krill (Euphausia superba) has a biomass of roughly 418,000,000 tonnes in the Southern Ocean, making it one of the most numerous organisms on the planet in terms of biomass. Whales, seals, penguins, squid, and a variety of fish species consume almost half of this biomass, many of which are significant commercial species.
Krill enables sunlight to be transformed from plant material to animal material, allowing energy to reach the planet. As a result, many other species, including some of the world’s biggest creatures, such as the blue whale, have access to this energy. Without a doubt, disrupting the habitats that support these krill species would have significant effects on many other species, including humans.
Not Like the Others
Although krill are commonly lumped together as a single animal, there are 86 separate species of krill divided into two groups. 85 of them are members of the Euphausiidae family’s ten genera. Bentheuphausia amblyops is the sole extant species in the Bentheuphausiidae family. B. amblyops thrives in deep seas below 3,300 feet, unlike many other krill species. It is a global species at this depth, occurring in all the world’s seas. It’s also the most basic krill species. This is significant in determining the evolutionary position of these species, which share characteristics with both decapods and mysids.
Apart from B. amblyops, all krill species are bioluminescent, with organs called photophores that can generate light. This light is produced via an enzyme-catalyzed process inside these organs. A luciferase enzyme, for example, activates luciferin, a particular pigment.
Interestingly, many krill species’ luciferin is a fluorescent tetrapyrrole, similar but not identical to the luciferin found in dinoflagellates, a kind of phytoplankton that can generate bioluminescence and is regularly ingested by krill. This indicates that the krill do not generate this chemical, but rather get it via their feed.
Photophores in krill are complicated organs with lenses that can be focused and rotated using muscles. The specific evolutionary purpose of these organs is unknown, although mating, social interaction, or direction are all possibilities. They might also be used as a type of counter-illumination camouflage to hide their shadow from ambient light.
It is thought that bioluminescence may operate as a defence against predation in certain bioluminescent creatures, successfully diverting and confusing their predators, especially in low-light circumstances such as at night or in the deep sea.