Abundance and trophodynamics of Euphausia crystallorophias in the shelf region of the Lazarev Sea during austral spring and summer

An investigation to estimate the seasonal changes in feeding habits in relation to the energy budget of Euphausia crystallorophias was carried out during austral spring and summer 1994/95 in the shelf region of the Lazarev Sea. Within the upper 300 m, concentrations of larvae, juveniles and subadults/adults of E. crystallorophias during December 1994 and January 1995 ranged from 27 to 1689, from 4 to 86 and from 2 to 9 ind. 1000 m−3, respectively. At stations where swarms of adults occurred, average abundances attained levels of 450–689 ind. 1000 m−3. Gut content analysis showed that during December micro- and mesozooplankton were the dominant components of the diet of E. crystallorophias, comprising on average 75% of the total number of identifiable food items. During January, however, the heterotrophic component of the diet decreased sharply and phytoplankton cells accounted for 68% of the total number of food particles. This suggests that E. crystallorophias may exhibit a predominantly carnivorous habit during austral spring. However, at the onset of the spring phytoplankton bloom, this species seems able to switch to a truly omnivorous habit.