Variation of lipid classes among organs of the Northern krill Meganyctiphanes norvegica, with respect to reproduction

Lipid content and class in the Northern krill Meganyctiphanes norvegica (digestive gland, stomach, gonad, fat body, abdomen) was investigated and correlated with sex and reproductive stage. Ready to spawn females, have high lipid content in ovaries, while in males and spent females, the major site of lipid deposits was the digestive gland, followed by the fat body. These differences among spawning and spent females are indicative of strong interactions between the ovary and digestive gland and the ovary and fat body during vitellogenesis. Triacylglycerols (TAG) were the major neutral lipid class with high levels in the digestive gland. The major phospholipid was phosphatidylcholine (PC) particularly in the muscular tissue of the abdomen. Phosphatidyl-ethanolamine (PE) and -serine-inositol (PS-PI), were present at intermediate levels. Reproductive males were depleted in TAG and diacylglycerols (DAG) in the digestive gland, gonad and fat body, and had 4 times lower cholesterol in the gonad than ready to spawn females. Furthermore, ready to spawn females had in the ovary higher amounts of TAG, DAG and phospholipids (PC, PE, PS-PI) than spent females. Linear relationships between lipid content and main lipid class (TAG, PC, PE, PS-PI) in different fractions of males and ready to spawn females showed that: (1). TAG was stored for both sexes in all cephalothorax fractions with highest values in the digestive gland and ovary fluid; (2). PC was accumulated for both sexes in the fat body and the gonad with a higher slope for females, with the highest values in the ovary fluid and in the abdomen of males and that (3). PS-PI was stored only in the ovary and abdomen of mature females. These results are discussed in terms of the strategy developed by Meganyctiphanes norvegica to allocate lipids to the next generation for optimised embryogenesis.

Studies on metabolic properties in the Northern Krill, Meganyctiphanes norvegica (Crustacea, euphausiacea): influence of nutrition and season on pyruvate kinase

The specific activity and the kinetic properties of partly purified pyruvate kinase (PK) (EC 2.7.1.40) from the Northern Krill, Meganyctiphanes norvegica, were investigated in relation to varying food resources. In order to evaluate the effect of starvation on the total energy metabolism, the respiration rates of fed and unfed krill were determined. The FPLC-elution profile of PK displayed two distinct peaks - PK I and II. The first isoform represented 80% of the total PK activity in the organism, and 20% was contributed by the second isoform. PK I was inhibited by ATP but was not influenced by fructose-1,6-bisphosphate (FBP). In contrast, PK II showed ATP inhibition and up to 2.5-fold increased activity by addition of 17 micromol.l(-1) FBP. The Michaelis-Menten constants of both isoforms were 2-10-fold higher for ADP than for phosphoenolpyruvate (PEP). Alanine showed no regulatory effect on PK I and II. In specimens starved for 7 days oxygen consumption decreased by 20%. Neither the feeding experiments nor the animals captured in the field during low and high productive seasons indicate that PK properties of M. norvegica are modified in relation to food supply. Accordingly, alternative mechanisms are involved in the depression of the metabolic rate in terms of oxygen consumption.

Spectral and Biochemical Characteristics of the Particulate Matter in Bedford Basin

A survey of the distribution, nature, and biochemical composition of particulate matter (less than 153 μm diam) showed that small particles (< 18 μm) made up the bulk of the particulate matter during most of the summer. Relatively large amounts of microzooplankton (tintinnids) were also recorded during the period of stable hydrographic conditions. Diatoms and dinoflagellates were abundant only in early fall prior to the fall bloom. All cell counts were transformed into parts per million on a volume basis to compare with Coulter Counter data. Cell counts on preserved samples strongly underestimated the number and volume of small particles and did not take into account the detritus. Considerations of the ATP content strongly suggested that for naturally occurring particulate matter there is not a constant ATP to carbon ratio but rather an upper and lower limit. Small particles were the main repository for protein whereas phytoplankton was the repository for carbohydrates. The high variability of both quality and quantity of particles in the neritic habitat suggests that a single chemical variable cannot describe fully the nutritive value of naturally occurring suspended matter. Key words: particulate matter, phytoplankton, microzooplankton, flagellates, protein, carbohydrates, ATP, carbon

The occurrence and distribution of octadecapentaenoic acid in a natural plankton population. A possible food chain index

It is shown that marine dinoflagellates under natural conditions synthesize the unusual fatty acid octapentadecaenoic (18:5omega3). This acid is very likely a characteristic of certain groups of phytoplankters and is not an artifact from artificial culture conditions. Various species of herbivorous copepods as well as contemporary carnivorous chaetognaths living in the same environment present traces of this fatty acid. The decreasing quantity of 18:5omega3 on moving up the food chain, and its absence in certain species, makes it a possible ecological tracer.