남극크릴의 생리상태 지표

Abstract

Recent studies have focussed on the biology of Antarctic krill during winter. Krill have the ability to employ a number of overwintering strategies including: omnivory, carnivory, dependence on ice algae, reduced metabolism and starvation and associated shrinkage. There is no certainty on the environmental conditions that result in krill employing one strategy over another. There are also few simple tests that can be used to determine which behaviour is being relied on by krill at any particular place or time. We have developed a series of simple methods, which have been validated in the laboratory and in the field, to indicate the nutritional condition of krill collected at any season. They are particularly applicable for studies in winter for which there is greatest uncertainty. The simplest measure that indicates the in situ nutritional condition of krill is the in vitro measurement of the length of the digestive gland relative to the length of the carapace. In animals that have been starved or in animals that have been collected during winter there is markedly reduced digestive gland length for a given size of krill. We propose a condition index based on this relationship. This index reflects relatively short term (< 7 days) food availability.Longer term food shortage (> 10 days) results in shrinkage in overall length in krill. There is still little consensus on how often this occurs in the wild. Krill that have undergone long periods of shrinkage are distinguishable from krill that have not shrunk by the relationship between the eyeball diameter and the total length. Shrinking krill conserve the eyeball diameter thus shrunk krill have larger relative eyeball size than un-shrunk krill of the same length. This index reflects food shortage over seasonal periods.Intermediate length nutritional condition can be measured by a number of parameters derived from the instantaneous growth rate methodology. This is an experimental technique that me