A biochemical and modelling study of the life history of Antarctic krill, Euphausia superba

Abstract

This thesis investigates various aspects of the energetics of Antarctic krill, Euphausia superba. In the first section, proximate chemical and elemental composition is examined in relation to life history, environmental variability and physiology. It is shown that life-history stage has a significant effect on both proximate and elemental composition. Krill growth in the field was found to differ markedly between individuals, so the observed variability in chemical composition is investigated with respect to differing growth rates in an attempt to derive a predictive relationship between elemental composition and growth in krill. It is shown that elemental composition cannot provide a proxy for short term variations in growth rate. A method is then developed which applied modified stoichiometric theory to krill to determine proximate composition from elemental composition data. It is possible to predict realistic chemical composition for all life history stages from elemental composition data which reflects that directly measured. In the second section, an energy budget model for Antarctic krill is developed, incorporating a novel representation of the energetic costs of growth. This model is then used to explore key aspects of the life history of krill (growth, maturity and reproductive success) under a range of environmental conditions. The model produced an ecologically realistic simulation of growth and reproduction in female krill. These simulations indicated that food availability and temperature have a highly significant role in determining the life history of krill, with a potentially significant knock-on effect to the Southern Ocean ecosystem. Results of the model predict an average growth rate of 0.05 mm d-1, but that in times of scarce food temperature has a significant effect on growth. A significant benefit to the animal occurs from being in cold waters during periods of limited food.