Abstract:
From the absracts of some of the referenced papers:
During a period of short-term (19 days) starvation, total lipid in the digestive gland of Euphausia superba Dana decreased from 21 to 9% dry weight. Total lipid per digestive gland decreased significantly during starvation compared to Day 0 individuals, falling from 1960 (plus or minus 172) TO 385 (plus or minus 81) micrograms. Polar lipid was
... the major lipid class utilised during starvation, falling from 1510 (plus or minus 225) to 177 (plus or minus 46) micrograms per digestive gland (76 to 45%). Absolute levels of tricylglycerol fell from 300 (plus or minus 41) to 76 (plus or minus 5) micrograms; however, relative levels remained unchanged. The relative level of free fatty acid increased significantly with starvation (4 to 39%) with absolute levels ranging from 79 (plus or minus 1) to 156 (plus or minus 20) micrograms per digestive gland. Absolute levels of all fatty acids per digestive gland declined continually until the end of the starvation period. The long-chain polyunsaturated acids eicosapentaenoic and docosahexaenoic, decreased with starvation from 37 to 36% and 15 to 10%, respectively whereas the saturated fatty acid, palmitic acid (16:0), increased from 15% to 22%. Cholesterol, the major sterol in this organ, increased from 17 (plus or minus 20) to 44 (plus or minus 13) micrograms per digestive gland by Day 3, and by Day 19 had returned to levels found in the digestive gland of Day 0 individuals. Desmosterol followed a similar pattern to cholesterol, increasing from 3 (plus or minus 1) micrograms per digestive gland on Day 0 to 11 (plus or minus 4) micrograms on Day 3, and falling to 2 (plus or minus 1) micrograms on Day 19. Other sterols in the digestive gland, predominantly of algal origin, fell from the levels found in Day 0 individuals to near zero amounts by Day 6. The digestive gland of E. superba plays a dynamic role during short term starvation in terms of lipid content and composition. The relative levels of polar lipids, free fatty acids and cholesterol in the digestive gland may provide reliable indices of the nutritional condition of E. superba in the field. Sterols in the digestive gland are indicative of recent dietary composition of krill, and may also be used to quantify dietary input from individual phytoplankonic species.
The fatty acid profiles of Euphausia superba, the Antarctic prymnesiophyte, Phaeocystis pouchetii, and a temperate diatom, Phaeodactylum tricornutum were analysed and compared. The lipid content, lipid class, fatty acid and sterol composition of E. superba fed on each cultured phytoplankton and a mixed diet of both species, were determined. No significant difference was found between total lipid levels of E. superba reared on each of these different diets. Phaeocystis pouchetii, although deficient in a number of the essential fatty acids, is apparently an adequate food source for E. superba. The proportion of polyenoic acids varied within lipid classes although there was no significant difference between levels of the long chain polyunsaturate 20:5 (n-3) in the total lipid of E. superba fed on these diets. This acid was found to be less than 1% of the total lipid in Phaeocystis pouchetii compared to 37% in Phaeodactylum tricornutum. This suggests that krill may possess the ability to convert exogenous shorter chain fatty acids to 20:5 (n-3) and 22:6 (n-3). Significant differences were detected in the isomeric ratio of 16:1 (n-7c)/16:0 between krill fed the diatom compared to the prymnesiophyte diet. Significant differences were also detected in several shorter chain fatty acids and between fatty acids within their lipid classes. Such differences may have the potential to be used as biochemical signatures to provide information on food sources and possible feeding grounds of E. superba. Phaeocystis pouchetii in a very late stationary phase, although not used in this feeding study, was found to contain 11% of 22:6 (n-3) for which there are few substantive sources in natural algal populations.
Freshly caught male and female Euphausia superba from the same swarm exhibited different rates of mortality subsequent to capture. Mortality was significantly higher for reproductive males (100%, n - 68) than for females (3%, n = 186) within the first 3 days of capture. Total lipid and triacylglycerol levels in male, female and juvenile Euphausia superba were analysed and compared. All reproductive male krill analysed from this swarm had low lipid levels (1 to 3% dry weight) with negligible triacylglyecerol stores (0 to 2% of total lipid). Somatic lipid stores in female and juvenile krill ranged from 8 to 30%, of which up to 40% was triacylglycerol. The levels of algal sterols in the digestive gland of males, females and juveniles indicate that all krill had been feeding recently. An analysis of the sex ratio of krill catches derived from data collected over seven summers from the Prydz Bay region showed a decrease in the proportion of males with increasing size. There was a sharp decline in numbers of male krill once they attained a length of 51 to 55mm. Low lipid levels in reproductive male krill may be due to reproductive costs. The resulting low storage-lipid levels are accompanied by high mortality in male krill.
Several aspects of copper toxicity to Euphausia superba were examined. Baseline copper concentrations in Euphausia superba caught and frozen in the Antarctic was found to be in the range 55.2-82.6 micrograms per gram, dry weight. Total body copper concentrations were measured in animals exposed to various ambient copper concentrations. Euphausia superba were able to regulate copper to a constant level beyond which copper became lethal at estimated ambient bioavailable copper ion concentrations of 140 million M at an LT50 of 3.25 days. Krill died when the total body concentration reached approximately 250-300 micrograms per gram dry weight. Survival rates were found to be directly related to free copper ion concentrations which were determined by altering the free cupric ion activity using the metal ion complexing agent, NTA. 
