CULLEN, M. F.*; HARRINGTON, S. T.; KAUFMANN, R. S. ; LOWERY, M. S.: Seasonal Changes in Physiological Status of Antarctic Krill, Euphausia superba, from Deception Island, Antarctica

Seasonal changes in biochemical indicators of physiological status were analyzed in abdominal muscle of the Antarctic krill, Euphausia superba, collected from Port Foster, Deception Island, in the South Shetland Islands, Antarctica. Krill were collected with a MOCNESS trawl during cruises in February, May, and November 1999. Muscle protein concentrations and activities of the glycolytic enzyme lactate dehydrogenase (LDH) and the mitochondrial enzyme citrate synthase (CS) were significantly lower in female krill when compared to males of similar size (P < 0.05). Female krill showed seasonal changes in LDH activity, with lowest values observed in early summer (11.99 � 2.45 units/g muscle) and highest values (23.27 � 5.18 units/g) in late summer. Male krill showed no seasonal differences in LDH activity. Both females (9.76 � 1.40 units/g) and males (12.03 � 3.37 units/g) showed highest CS activities late in summer. Females had the lowest CS activity (6.51 � 3.08 units/g) in early summer, whereas males showed the lowest CS activity during early winter (6.00 � 3.60 units/g). Adult and late stage juvenile krill survive through the winter when phytoplankton production is greatly reduced. Lower CS values suggest that krill exhibit a reduced metabolism during the winter, perhaps enhancing survival. Males maintain higher activities of LDH and CS, indicating that their burst and aerobic swimming performance may be higher than that of females throughout the year. Lower enzyme activities in female krill suggest that they may divert more energy to reproduction than do males and achieve greater metabolic suppression during overwintering.