MEPS prepress abstract  -  doi: 10.3354/meps07366

ABSTRACT: A biochemical model of Antarctic krill (Euphausia superba) was developed to investigate the physiological mechanisms which enable krill to survive winter when food is scarce. In this modeling approach data sets on the biochemical composition of krill and its food sources are combined into a model that takes food quality into account rather than just food availability during different seasons. Krill is defined in terms of protein, neutral lipid, polar lipid, carbohydrate, chitin, and ash content and the model tracks krill neutral lipid content separately from weight. The model includes parametrizations of filtration, ingestion, and metabolic processes which determine krill growth rate. Changes in the initial ratios of protein, neutral lipid, polar lipid, carbohydrate, and chitin occur in response to the biochemical composition of available food as krill grows. Model results show that a diet of phytoplankton food alone may be sufficient for krill to grow to observed sizes but may not be sufficient to provide summer lipid resources as they are observed in the field and that are necessary for krill to reproduce and survive winter. The inclusion of sea ice algae of additional food is beneficial for krill at the end of winter but does not significantly change summer krill lipid content. However, the amount of lipids accumulated within krill increases significantly when krill feeds on lipid rich heterotrophic food which points to the importance of carnivory, even in times when phytoplankton food is available. The strategy of combusting body structure for energy through the process of shrinking is found to provide most energy to krill of all sizes during times of prolonged starvation