Krill

One of the smallest and most vital animals living in the Antarctic Ocean is the krill (Euphausia superba). There are nearly 90 species of krill and they are all strictly marine animals and cannot live in freshwater or on land. Because they are from the subphylum Crustacea, they most resemble common day shrimp and are abundant in the cold waters near the poles. They are a primary source of food for many whales, particularly the whalebone whales. Krill also contribute to the diet of many other animals such as seals, penguins, herring, sardines, many birds, and maybe, in the future, humans.
Krill bodies are made up of three different parts: the head, the thorax, and the abdomen. Often thought of as the insects of the ocean, krill do not actually come from the insect family, but do resemble them in many ways. The head consists of eyes and antennae; the thorax is composed of several thoracic appendages; and the abdomen has the tail, the gills and a unique substance called the photopore. Krill photopores are complex organs with lenses that have focusing abilities using special muscles to rotate them. The genus name classification for krill is called Euphausia. Euphausids, with the exception of a species called Bentheuphausia amblyops, use these photopores to emit a brilliant blue-green light. The light is generated by an enzyme-catalyzed chemoluminescence reaction, wherein a kind of pigment called luciferin is activated by a luciferase enzyme. Researchers do not know the precise function of these organs up to now, but suspect they may have a purpose in mating, social interaction, or in orientation. Some researchers believe the light is a form of counter-illumination that compensates their shadow against the ambient light from above, which makes it more difficult to predators to see from below.
Most euphausids range from ¼ to 2 inches and many are transparent. There have been recorded species of krill living in bathypelagic environments reaching lengths of 6 inches. They live at considerable depth during the day and then migrate extensively to the surface layers of the ocean at night. Some species that live in the deep parts of the sea have been caught at depths of 6000 feet. When krill dive to such depths, their photopores come into use to light up their bodies.
The feeding appendages, which consist not only of the mouth but also the anterior parts of the thorax, are elaborate and can be used in several ways. This enables the animal to filter food particles from the water, collect organic material from the surface of the sediment, or catch live prey. The krill’s diet consists of mainly phytoplankton, small crustaceans, and detrital matter.
The male reproduction system is extremely complex and is the main criterion for specific identification of the male. During the process call swarming, the male transfers a spermatophore to the spermatheca of the female at copulation. The early embryos usually live freely in the sea, however, those of some 25 species are carried attached to the to the abdominal regions of the thorax. The larval stages are numerous. The first stage (nauplius) is when the baby krill hatches from the egg membranes and develops into the second stage (metanauplius). Three stages follow during which the abdomen and stalked eyes develop. All species of krill pass through these stages. The succeeding stages vary between species and within species in different localities and at different times. Sexual maturity for other species of krill is normally achieved at an age of 1 year; however, E. superba and those living in bathypelagic environments require 2 years or more before maturity is achieved.
The digestive system for most crustaceans is a relatively straight tube that curves dorsally from the mouth, which is on the underside of the head. In the anterior portion of the body is a complex and elaborate grinding mechanism called the gastric mill. The posterior chamber is divided into dorsal and ventral filtering compartments for the straining of food.
The species of Euphausia Superba is so abundant–as many as 48,000 individuals exist in a cubic yard of seawater–that it is the principal, if not the only, food of the Antarctic blue whale, the largest animal known. Their diet of three million calories per day not only must meet their immediate needs but must also furnish energy reserves, stored as blubber, for the rest of the year. One pound of E. superba provides 460 calories. Thus, blue whales eat approximately 3 tons of these krill a day.
Before the whaling industry decimated the population of blue whales, there were perhaps a half a million of them at any one time, consuming about 270 million tons of krill during the Antarctic summer. Even more amazing is the fact that this only accounts for 20% of the total krill population.
Of the minerals contained in a krill’s body, some deserve special mention because of their value to the creatures that consume them. Copper, which is actually more concentrated in krill than in fish meal, is found with resides of lysine, an important fatty acid, and has an important role in the formation of collagen and the integrity of fins and skin. Selenium, which is also more concentrated in krill than in fish meal, is an important player in the glutathione system.
As food, krill is rich in protein. However, various problems must be overcome before krill can provide a source of protein-rich food for people. For example, efficient harvesting methods must be developed to make large-scale krill fishing economically profitable. But more importantly, researchers need to determine whether such a large catch would jeopardize the food supply of other animals that eat krill. Scientists and biologists are still working on these problems.
If krill were to be exploited for commercial fishery, the possible yield would range from 27-180 X 10^6 tons per year. Krill can be easily located because they travel and live in huge swarms, and therefore are easy to catch. Krill pastes and meal can be manufactured to feed domestic animals or to use in therapeutic diets. Krill sausages, krill-stuffed eggs, and shrimp butter are already marketable products in Japan, Russia and Germany.
Krill’s importance in the food chain is more than obvious when you see the amount that is consumed by Antarctic animals and its ability to thrive through the centuries. The blue whale is incredibly dependent on krill as a part of its diet. Phenomenal amounts of krill are born each day, enough to supply all the animals that depend on it. They are truly amazing creatures. Despite the enormous quantity and tiny size of these creatures, they are still miraculously complex. Therefore, the krill loudly proclaims the existence of an Intelligent Designer.