Seasonal variation in biochemical indicators of physiological status in Euphausia superba from Port Foster, 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, an active volcano located in the Shetland Island chain west of the Antarctic Peninsula. Krill were collected with a 10 m2 MOCNESS trawl during four cruises (November 1999, February, May, November 2000). RNA:DNA mirrored the chlorophyll a concentration, with the highest values found during seasons of abundant phytoplankton. Activities of the glycolytic enzyme lactate dehydrogenase (LDH) and the mitochondrial enzyme citrate synthase (CS) were significantly higher in male krill when compared to females of similar size, indicating that their burst and aerobic swimming performance may be higher than females throughout the year. RNA:DNA ratio and enzyme activities were highly elevated in summer as compared to the earliest spring sampling period. Krill showed significant seasonal changes in LDH activity, with lowest values in spring and highest values in summer (females) or autumn (males). Krill showed significant seasonal changes in CS activity with highest values in summer. Protein and % water varied significantly among seasons for both males and females. Lower CS activity and RNA:DNA ratio suggest krill exhibit reduced metabolism during the winter when phytoplankton production is reduced, perhaps enhancing survival. Lower enzyme activities in female krill in early spring suggest they may achieve greater metabolic suppression during overwintering.