Seasonal variations of lipids (wax esters, fatty acids and alcohols) in calanoid copepods from the North Sea

Abstract

Wax esters, fatty acids and fatty alcohols of the total lipid of Calanus finmarchicus, C. helgolandicus and Pseudocalanus elongatus were investigated during each season of 1983 in the Fladen Ground area and in the eastern North Sea. Wax esters were generally the main lipid class, with up to 88% in copepodid stage V. The wax ester proportion of the females was much more variable than that of the copepodid stages, ranging from 2.6 to 79% of total lipid. The fatty acid compositions showed a high variability and diversity throughout the seasons. The fatty acids of Calanus, dominating all stages and seasons, were the polyunsaturated acids 22:6 and 20:5 and the saturated acids 16:0 and 14:0. The major alcohols were 22:1, 20:1 and 16:0. In Pseudocalanus elongatus dominance of the 16:0 alcohol and substantial amounts of the 18:1 acid were found in addition, which indicates that the enzymatic system for chain elongation and desaturation is less developed in this small copepod. During spring, the fatty acid composition reflected the diatom food by increasing levels of the 20:5 acid. When food becomes scarce, e.g. during winter or even in summer, the fatty acid compositions were nearly reduced to the three main acids: 16:0, 20:5 and 22:6. Differences between C. finmarchicus and C. helgolandicus seem not to be species dependent but are caused by environmental conditions such as quality, quantity and composition of food. Thus, in C. helgolandicus, the differences in biochemical composition were less pronounced, probably owing to the better food conditions at the near-shore sampling location throughout the year.