The Organism

As a result of the extensive collections made during the Discovery II investigations in the 1920s and 1930s, almost all that is known about krill comes from the classic studies of the late J.W.S. Marr during that expedition (Marr, 1962). Of the 11 species of Antarctic krill, interest centres around Euphausia superba, E. crystal-lorophias, Thysanoessa macrura, and £. valentini. These euphausiids are located as follows : E. valentini is found north of the Polar Front; E. crystallorophias inhabits the pack-ice zone; and E. frígida and E. superba are found in open waters south of the Polar Front. Although E. superba (Fig. 8.15) is often considered to be synonymous with krill and, indeed, is the dominant species, a number of other euphausiids which are particularly important at the ice-edge should be included under the term.

Due to the circumpolar distribution of the Antarctic krill and the apparent similarity of the biology, breeding, and swarming of krill from the Atlantic, Pacific and Indian Sectors, the following discussion of krill for circum-Antarctic waters is pertinent to the Pacific Sector krill population.

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