Book excerpt: This book gives a unique insight into the current knowledge of krill population dynamics including distribution, biomass, production, recruitment, growth and mortality rates. Detailed analysis is provided on food and feeding, reproduction and krill behaviour. The volume provides an overview on the aspects of natural challenges to the species, which involve predation, parasites and the commercial exploitation of the resource and its management. A chapter on genetics shows the results of population subdivision and summarizes recent work on sequencing transcriptomes for studying gene function as part of the physiology of live krill. The focus of Chapter 4 is on physiological functions such as biochemical composition, metabolic activity and growth change with ontogeny and season; and will demonstrate which environmental factors are the main drivers for variability. Further discussed in this chapter are the bottle necks which occur in the annual life cycle of krill, and the mechanisms krill have adapted to cope with severe environmental condition.