Difference between revisions of "Antarctic krill"

'''Antarctic krill''' ('''''Euphausia superba''''') is a species of [[krill]] found in the [[Antarctica|Antarctic]] waters of the [[Southern Ocean]]. It is a small, swimming crustacean that lives in large schools, called swarms, sometimes reaching densities of 10,000–30,000 individual animals per cubic meter. It feeds directly on minute phytoplankton, thereby using the primary production energy that the phytoplankton originally derived from the sun in order to sustain their open ocean life cycle.

'''Antarctic krill''' ('''''Euphausia superba''''') is a species of [[krill]] found in the [[Antarctica|Antarctic]] waters of the [[Southern Ocean]]. It is a small, swimming crustacean that lives in large schools, called swarms, sometimes reaching densities of 10,000–30,000 individual animals per cubic meter. It feeds directly on minute phytoplankton, thereby using the primary production energy that the phytoplankton originally derived from the sun in order to sustain their open ocean life cycle.

===Bioluminescence===

===Bioluminescence===

Krill are often referred to as ''light-shrimp'' because they can emit light, produced by bioluminescent organs. These organs are located on various parts of the individual krill's body: one pair of organs at the eyestalk, another pair on the hips of the second and seventh thoracopods, and singular organs on the four pleonsternites. These light organs emit a yellow-green light periodically, for up to 2–3 seconds. They are considered so highly developed that they can be compared with a torchlight: a concave reflector in the back of the organ and a lens in the front guide the light produced, and the whole organ can be rotated by muscles. The function of these lights is not yet fully understood; some hypotheses have suggested they serve to compensate the krill's shadow so that they are not visible to predators from below; other speculations maintain that they play a significant role in mating or schooling at night.

Krill are often referred to as ''light-shrimp'' because they can emit light, produced by bioluminescent organs. These organs are located on various parts of the individual krill's body: one pair of organs at the eyestalk, another pair on the hips of the second and seventh thoracopods, and singular organs on the four pleonsternites. These light organs emit a yellow-green light periodically, for up to 2–3 seconds. They are considered so highly developed that they can be compared with a torchlight: a concave reflector in the back of the organ and a lens in the front guide the light produced, and the whole organ can be rotated by muscles. The function of these lights is not yet fully understood; some hypotheses have suggested they serve to compensate the krill's shadow so that they are not visible to predators from below; other speculations maintain that they play a significant role in mating or schooling at night.

==Geographic distribution==

==Geographic distribution==

Antarctic krill have a circumpolar distribution, being found throughout the [[Southern Ocean]], and as far north as the [[Antarctic Convergence]]. At the Antarctic Convergence, the cold Antarctic surface water submerges below the warmer subantarctic waters. This front runs roughly at 55° south; from there to the continent, the Southern Ocean covers 32 million square kilometers. This is 65 times the size of the North Sea. In the winter season, more than three-quarters of this area become covered by ice, whereas 24,000,000 km2 become ice free in summer. The water temperature fluctuates at -1.3 C (3 F).

Antarctic krill have a circumpolar distribution, being found throughout the [[Southern Ocean]], and as far north as the [[Antarctic Convergence]]. At the Antarctic Convergence, the cold Antarctic surface water submerges below the warmer subantarctic waters. This front runs roughly at 55° south; from there to the continent, the Southern Ocean covers 32 million square kilometers. This is 65 times the size of the North Sea. In the winter season, more than three-quarters of this area become covered by ice, whereas 24,000,000 km2 become ice free in summer. The water temperature fluctuates at -1.3 C (3 F).