Friday 8 February 2008 à 12:54

The Krill

Par Philippe Koubbi. Correspondent aboard the Umitaka Maru

(By Graham Hosie of the Australian Antarctic Division, CEAMARC program leader)
This group is common in all marine systems. There are five abundant species in Antarctic and Southern Ocean waters.

Euphausia superba, the Antarctic krill, is the largest species in the region, reaching 60 mm in total length, and is the most abundant at about 200 to 500 million tonnes. It is a key component of the Antarctic food web, but not the sole key link. Numerous vertebrate predators, fish, penguins, flying seabirds, seals and whales are dependent on this species, but other zooplankton and euphausiids are also important alternative links in the food web. E. superba has a circumpolar distribution, but has localized regions of higher abundances, especially near the continental shelf edge. This species is primarily herbivorous, but will switch to omnivory/carnivory feeding is necessary.

Euphausia crystallorophias, the ice or crystal krill, is a coastal species. The adults are restricted to the colder waters, usually < -1º C, of the continental shelf. Larvae may be found north of the shelf by offshore currents. This species is small than E. superba at about 35 mm total length, but within their range they are extremely abundant. They are important in the diet of various fish and birds nesting in coastal margins. Crystal krill form a large component of the diet of breeding Adele penguins around Dumont d’Urville, Mawson and Davis. Minke whales are known to feed on this species.

Some representatives of krill, © P. Pruvost.

The species name of Euphausia triacantha refers to the three spines dorsal on the abdomen. It is similar in size to crystal krill. Little is known about this species other than that it is mainly mesobathypelagic but migrates into the upper 200 m at night.

Euphausia frigida prefers the waters of the Antarctic Circumpolar Current north of the sea ice zone. They are a smaller species, generally about 20 mm in length but are reasonably abundant. The biology of this species has received little attention.

Thysanoessa macrura or big-eye krill, is perhaps the most abundant species numerically. However, their smaller size of <28 mm means their biomass is less than that of Antarctic krill. They have a wide circumpolar distribution extending south of the Sub-Antarctic Front to the Antarctic coast. They have a bi-lobed eye, hence their common name, and a pair of prehensile elongated thoracic legs. The presence of these limbs led to the assumption that the species is a predator, but they can feed extensively on phytoplankton and are now considered omnivores. Despite their high abundances and wide distribution, little is known about their role in the Antarctic marine food web.



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