Ecological investigations on the zooplankton community in Balsfjorden, Northern Norway: seasonal changes in the lipid class composition of Meganyctiphanes norvegica (M. Sars), Thysanoessa raschii (M. Sars), and T. inermis (Krøyer)

Abstract

The lipid class composition of three krill species, Meganyctiphanes norvegica (M. Sars), Thysanoessa raschii (M. Sars), and T. inermis (Krøyer), was determined throughout the year in Balsfjorden, Northern Norway. Meganyctiphanes norvegica had triglycerides as its major neutral lipid, Thysanoessa raschii had mainly triglycerides with small amounts of wax esters, whereas T. inermis had mainly wax esters with lesser amounts of triglycerides. Neutral lipids were generally accumulated by the krill during spring-early summer, maintained at high levels through to mid-winter and then declined to minimal levels during early spring. Differences in rates of deposition and mobilization of neutral lipid between males and females occurred in Meganyctiphanes norvegica and Thysanoessa raschii but not in T. inermis. T. raschii accumulated lipid somewhat later in the year than T. inermis but earlier than Meganyctiphanes norvegica. A major rôle for lipid in the elaboration of gonads is indicated. The accumulation of either wax esters or triglycerides by euphausiids is considered in terms of the feeding habits and ecological niche differentiation of the species.