Influence of seasonal light conditions on the physiology of Antarctic krill Euphausia superba: Implications for over-winter biology and maturity development

Antarctic krill (Euphausia superba) is the most abundant of the world's euphausiids and plays a central role in the Southern Ocean pelagic ecosystem. The main focus of this thesis was to evaluate the influence of seasonal light conditions on the physiology of krill, particularly with regard to the over-winter biology and maturity development of krill. The results indicate that, irrespective of food supply, the level of feeding and metabolic activity in krill correlates with the degree of prevailing light conditions. Furthermore, the results indicate that the succession of female and male krill maturity stages is accelerated by light conditions of prolonged photoperiod and enhanced light intensity. Together, the results emphasizes the role of the Southern Ocean light regime as an essential cue governing the seasonal cycle of krill physiology. It is further shown that the photoperiodic response system in krill is not based on melatonin as a transducer of photoperiodic information, although melatonin is assumed to be principally involved in the transduction of photoperiodic information in living organisms