Scientific classification:
Phylum: Arthropoda
Class: Malacostrata
Order: Euphausiacea
Family: Euphausiidae
What does it look like? Th e Antarctic krill can be about 6 cm long when fully grown, and it
is more or less transparent, with a pair of big black eyes. The antennae are long and sprout
from the very front of the head. The thorax bears several pairs of specialized limbs that
form a basket like structure. Th e abdomen has several pairs of swimming limbs and ends
in a paddle called the telson.
Where does it live? This crustacean is found in the southern waters surrounding the continent
of Antarctica. Their preferred habitat varies depending on how old they are. As
youngsters, they dwell at great depths, but young adults and adults spend their time in
surface waters.
Swarming Crustaceans
There can be few animals whose importance in the planet’s ecosystems is as great as the Antarctic
krill. Singly, they are not that impressive. They look like a myriad of other shrimp like animals, but
what they lack in appearance they more than make up for in sheer abundance. The life of an Antarctic
krill starts as a fertilized egg, about the size of a period, sinking into the abyss. As the egg
descends, its cells divide and differentiate to form the young larva. At a depth of between 2,000
and 3,000 m, the baby krill hatches and begins to ascend, developing and growing as it makes
slow but steady progress through the icy waters, sustained by the remaining yolk from its egg.
There are around 86 species of what can be described as krill. Regardless of the
species, they are all considered keystone species in marine ecosystems. They occur in
such huge numbers that many animals depend solely on them for food. The huge
cetaceans, like the blue whale, are a good example. Their diet consists of krill and
whatever else happens to be swimming among the swarm.
• The total mass of Antarctic krill in the ocean during the peak of the season is estimated
to be on the order of 125–725 million tonnes, making this species probably
the most successful animal on the planet, in terms of biomass at any rate.
• For reasons that are not fully understood, krill numbers go through cyclical peaks
and troughs that are thought to be linked to the abundance of pack ice surrounding
Antarctica. In years where there is lots of pack ice, it provides numerous little nooks,
crannies, and caverns in which the young krill can shelter from their many predators.
They appear to suffer when there is little pack ice. In these lean years, they are replaced
as the dominant plankton animal by jelly-bodied creatures called salps.
• In some areas of the Southern Ocean there are unusual places rich in nutrients,
but where the diatoms and other photosynthesizing, single-celled organisms are surprisingly rare. As there is no food for them, the krill are absent from these areas.
It turns out that these odd tracts of ocean lack iron. Injecting iron gives the plantlike
organisms what they need, and before long they bloom, attracting the attention of the
gigantic swarms of krill. It has been suggested that ships could circle the Southern
Ocean and inject iron into the water. Th is would stimulate the diatom populations
and, in turn, the krill, providing a way of engineering the environment to increase the
amount of carbon dioxide that is locked away in the deep ocean.
• Around 100,000 tonnes of this Antarctic krill species, Euphausia superba, is taken
every year for animal and human consumption. In Japan, processed krill is known as
okiami.
• The Antarctic krill, like all its relatives, sheds its skin very regularly. It is peculiar not
only for the speed with which it can do this but also for its ability to grow smaller
at each successive molt if food is scarce. The Antarctic krill can quite literally jump
out of its old skin, leaving the skin floating in the water, where it may act as decoy to
confuse predators.
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