Field observations on the developmental ascent of larval Euphausia superba (Crustacea)

Summary

Marr's (1962) hypothesis on the descent of eggs and ascent of early larvae of Euphausia superba is examined in the light of investigations prior to and including field investigations in January 1985. Two deep stations (4100 m) west of the South Orkney Islands yielded more than 6600 eggs and early larvae per 100 m³ in the 1000 to 2000 m layer; also below 2000 m eggs and naupliar stages occurred. Sinking speed and sinking depth of krill eggs are discussed in the light of laboratory experiments of Marschall (1983), Quetin and Ross (1984), and George and Strömberg (1985). Hatching depths calculated from the experimental data on sinking rate and incubation time tend to be shallower than the deep occurrence of krill eggs at sea. Possibly krill may spawn not only near the surface but also at depths of several hundred meters. The high abundance of naupliar stages in smaples from our deepest layer corrobrate the presumption of Marschall and Hirche (1984) that the nearly immobile nauplii still sink and that the larvae begin to rise only when they have reached the metanaupliar stage.