Krill

Krill are little crustaceans that live in all of the world's oceans and belong to the order Euphausiacea. The word "krill" comes from the Norwegian word krill, which means "small fry of fish" and is typically applied to fish species.

Krill are a crucial trophic level link, as they are near the bottom of the food chain. They eat phytoplankton and (to a lesser extent) zooplankton, but they are also the primary food source for many larger creatures. The Antarctic krill, Euphausia Superba, has an estimated biomass of over 379,000,000 tonnes in the Southern Ocean, making it one of the species with the highest total biomass. Whales, seals, penguins, squid, and fish consume more than half of this biomass each year. The majority of krill species migrate vertically on a daily basis, providing food for predators at the surface at night and deeper depths during the day.

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Krill Scientific Classification

• Kingdom: Animalia

• Phylum: Arthropoda

• Subphylum: Crustacea

• Class: Malacostraca

• Superorder: Eucarida

• Order: Euphausiacea

Krill Distribution and Habitat

Although krill can be found in all oceans, several species are endemic or have neritic (coastal) ranges. Within its deep-sea habitat, Bentheuphausia amblyopes, a bathypelagic species, has a worldwide distribution. Thysanoessa species can be found in both the Atlantic and Pacific oceans. Euphausia pacifica is found in the Pacific Ocean. From the Mediterranean Sea to the North Atlantic, northern krill can be found.

The four species of Nyctiphanes in the genus Nyctiphanes have neritic ranges. They're abundant along the California, Humboldt, Benguela, and Canaria’s current systems' upwelling zones.

E. crystallorophias, which is endemic to the Antarctic shoreline, is another species with a neritic distribution.

Nyctiphanes capensis, found only in the Benguela current, E. mucronata, found only in the Humboldt current, and the six Euphausia species exclusive to the Southern Ocean are among the species having endemic distributions.

There are seven species in the Antarctic, one in the genus Thysanoessa (T. macrura) and six in the genus Euphausia. Antarctic krill (Euphausia Superba) may live at depths of up to 100 metres (330 feet), but ice krill (Euphausia crystallorophias) can live at depths of up to 4,000 metres (13,100 feet), though they usually dwell at 300–600 metres (1,000–2,000 feet). Both are found south of 55 degrees south latitude, with E. crystallorophias dominant south of 74 degrees south latitude and in pack ice locations. E. frigida, E. longirostris, E. triacantha, and E. vallentini are some of the other species found in the Southern Ocean.

Anatomy and Morphology of Krill

Krill are decapod crustaceans with a chitinous exterior skeleton, as do all crustaceans. Their bodies are made up of three parts: the cephalothorax, which is made up of a merged head and thorax, the pleon, which bears the 10 swimming legs, and the tail fan. In most krill species, the outer shell is translucent.

Krill has complex compound eyes. Screening pigments are used by some species to adapt to varied illumination situations.

They have two antennae and a number of thoracic legs known as pereiopods or thoracopods, which are attached to the thorax. The number of them varies by genera and species. Feeding and grooming legs are among the thoracic legs.

As decapods, krill have five pairs of swimming legs called "swimmerets," which are strikingly similar to those of a lobster or a freshwater crayfish.

As adults, most krill are roughly 12 centimetres (0.4–0.8 inches) in length. A few species can reach 6–15 centimetres (2.4–5.9 in) in length. Thysanopoda spinicauda, the largest krill species, thrives in the open ocean. The externally visible gills of krill separate them from other crustaceans such as genuine shrimp.

Krill, with the exception of Bentheuphausia amblyopes, are bioluminescent animals with light-emitting organs called photophores. An enzyme-catalyzed chemiluminescence reaction produces light when a luciferin (a type of pigment) is activated by a luciferase enzyme. Many krill species' luciferin is a fluorescent tetrapyrrole that is similar but not identical to dinoflagellate luciferin, according to studies. Krill do not generate this chemical themselves, but rather get it through their diet, which includes dinoflagellates. Muscles can rotate krill photophores, which are complex organs with lenses and focusing powers. The exact purpose of these organs is uncertain; possible functions include mating, social interaction, direction, and counter-illumination camouflage to compensate for their shadow against overhead ambient light.

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Krill Feeding Habits

Many krill are filter feeders, with their thoracopods forming very thin combs with which they may filter their food from the water. These filters can be quite small in species that feed predominantly on phytoplankton, particularly diatoms, which are unicellular algae (such as Euphausia spp.). Although most krill species are omnivorous, a few are carnivorous, feeding on small zooplankton and fish larvae.

Krill are an essential component of the aquatic food web. Krill convert their prey's primary production into a form that can be consumed by larger creatures that can't eat the microscopic algae directly. Northern krill and other zooplankton-hunting species have a small filtering basket and actively seek copepods and larger zooplankton.

Krill Predators

Krill is consumed by a wide range of creatures, from little fish and penguins to giant seals and baleen whales.

Ecosystem disruptions that result in a krill population collapse can have far-reaching consequences. For example, during a coccolithophore bloom in the Bering Sea in 1998, the diatom concentration in the afflicted area plummeted. Because krill cannot feed on the smaller coccolithophores, the krill population (mostly E. Pacifica) in that region plummeted. Other species suffered as a result: the shearwater population plummeted. It was assumed that the incident was one of the reasons why salmon did not spawn that year.

Several single-celled endoparasitoid ciliates belonging to the genus Collinia can infect krill species and decimate populations. Thysanoessa inermis was found to have disease in the Bering Sea, as well as E. Pacifica, Thysanoessa spinifera, and Thysanoessa gregaria off the coast of North America. Some Dajidae (epicaridean isopods) ectoparasites plague krill (as well as shrimp and mysids); one such parasite is Oculophryxus bicaulis, which has been identified on the krill Stylocheiron affine and S. longicorne. It clings to the animal's eyestalk and sucks blood from its head; it appears to prevent the host from reproducing, as none of the afflicted animals reached adulthood.

Another hazard to krill populations is climate change.

Krill Life Cycle and History

Despite modest differences in detail from species to species, the life cycle of krill is relatively well characterized. Krill go through multiple larval stages after hatching, including nauplius, pseudometanauplius, metanauplius, calyptopsis, and furcilia, each of which is divided into sub-stages. The pseudometanauplius stage is only found in "sac-spawners," or species that lay their eggs in an ovigerous sac. As the larvae mature, they grow and moult several times, eventually replacing their tough exoskeleton when it becomes too small. Moulting occurs more frequently in smaller animals than in larger mammals. The larvae are fed by the yolk reserves in their bodies during the metanauplius stage.

By the time they reach the calyptopsis stage, differentiation has advanced far enough for them to build a mouth and digestive tract, and they are ready to feed phytoplankton. By that time, the larvae must have used their yolk reserves and reached the photic zone, the upper layers of the water where algae thrive. Segments with pairs of swimmerets are introduced to the furcilia stages, starting at the frontmost segments. Only at the next moult does each new pair become functional. Depending on environmental conditions, the number of segments added during any of the furcilia stages can vary even within one species. After passing through the last furcilia stage, an immature juvenile emerges in the shape of an adult, develops gonads, and grows sexually.

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Reproduction

The male deposits a sperm bag at the female's vaginal opening during mating season, which varies by species and climate (named thelycum). Females can have thousands of eggs in their ovary, which can account for up to a third of the animal's body weight. In a single season, krill can have many broods, with interbreed periods on the order of days.

There are two types of spawning mechanisms used by krill. The 57 species of Bentheuphausia, Euphausia, Meganyctiphanes, Thysanoessa, and Thysanopoda are "broadcast spawners," meaning the female releases the fertilized eggs into the water, where they sink, spread, and die. These species typically hatch as nauplius 1 stages but have recently been discovered to hatch as metanauplius or even calyptopis stages as well. The remaining 29 species in the other genera are "sac spawners," meaning the female carries the eggs with her until they hatch as metanauplii, though certain species, such as Nematoscelis difficilis, may hatch as nauplius or pseudometanauplius.

Moulting

When a specimen outgrows its stiff exoskeleton, it moults. Young animals moult more frequently than older and larger animals because they are growing faster. Moulting frequency varies greatly per species, and even within a species, it is influenced by a variety of external factors including latitude, water temperature, and food supply. Nyctiphanes simplex, a subtropical species, with an overall inter-molt interval of two to seven days: larvae moult every four days on average, whereas juveniles and adults moult every six days.

Inter-moult periods have been observed for E. Superba in the Antarctic sea, ranging from 9 to 28 days depending on temperature between 1 and 4 °C (30 and 39 °F), and for Meganyctiphanes norvegica in the North Sea, ranging from 9 to 28 days depending on temperature between 2.5 and 15 °C (36.5 and 59.0 °F).

Human Uses of Krill

Since at least the 19th century, and maybe earlier in Japan, where it was known as okiami, krill has been harvested as a food source for people and domesticated animals. Fishing on a large scale began in the late 1960s and early 1970s and is presently restricted to Antarctic waters and the seas around Japan. Japan and the Soviet Union, or, following the latter's disintegration, Russia and Ukraine, were historically the two greatest krill fishing nations. The harvest, which peaked in 1983 at around 528,000 tonnes in the Southern Ocean alone (of which the Soviet Union received 93 %), is currently regulated to avoid overfishing.

The fall in krill fishing began in 1993 when Russia left the industry and the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) established maximum harvest limitations for the sustainable exploitation of Antarctic krill. The Commission decided not to alter the quota following a review in October 2011.

Krill Oil Benefits and Uses

Krill oil comes from a tiny shrimp-like creature. The word "krill" means "whale food" in Norwegian. The oil from krill is extracted, put into capsules, and used as medicine.

Krill Oil Use: There are many Krill oil uses in our day-to-day life. Dry eye is treated with red krill oil. It's also used to treat hypertriglyceridemia (excess triglycerides in the blood), hyperlipidemia (excess cholesterol or other fats in the blood), and other illnesses, although there's little scientific evidence to back up these claims.

Some of the Krill Oil Benefits are Stated Below:

• In comparison to fish oil and the placebo, krill oil (1 to 3 g/day) was found to be helpful in lowering total cholesterol, LDL cholesterol, and triglycerides while boosting HDL cholesterol levels.

• According to a 2007 review, consuming 1 gram of krill oil twice a day for 90 days resulted in a considerable reduction in premenstrual syndrome (PMS) symptoms, with inflammation being one of the main causes.