Description: Lipid content, fatty acid composition, and feeding activity of the dominant Antarctic copepods, Calanoides acutus, Calanus propinquus, and Metridia gerlachei, were studied at a quasi-permanent station in the eastern Weddell Sea in December 2003. During 3 weeks of the spring phytoplankton development, total lipid levels of females and copepodite stages V (CVs) of C. acutus were almost doubled. Meanwhile, only a slight increase in total lipid content occurred in M. gerlachei, and no clear trend was observed in lipids of C. propinquus females. The pronounced increase of lipids in C. acutus was due to an accumulation of wax esters. The proportion of wax esters in the lipids of M. gerlachei was clearly lower, while triacylglycerols played a more important role. In C. propinquus, triacylglycerols were the only neutral lipid class. There were no pronounced changes in the feeding activity of M. gerlachei, whereas the feeding activity of C. acutus had rapidly increased with the development of the phytoplankton bloom in December, which explains its rapid lipid accumulation. The combination of gut content and fatty acid trophic marker analyses showed that C. acutus was feeding predominantly on diatoms. The typical diatom fatty acid marker, 16:1(n-7), slightly decreased and the tracer for flagellates, 18:4(n-3), increased in females and CVs of C. acutus. This shift indicates the time, when the significance of flagellates started to increase. The three copepod species exhibited different patterns of lipid accumulation in relation to their trophic niches and different duration of their active phases. The investigations filled a crucial data gap in the seasonal lipid dynamics of dominant calanoid copepods in the Weddell Sea in December and support earlier hypotheses on their energetic adaptations and life cycle strategies.

Description: Ocean warming and acidification will be most pronounced in the Arctic. Both phenomena severely threat thecosome pteropods (holoplanktonic marine gastropods) by reducing their survival (warming) and causing dissolution of their aragonitic shell (acidification). Lipids, particularly phospholipids, play a major role in veligers and juveniles of the polar thecosome pteropod \textit{Limacina helicina} (Phipps 1774) comprising over two thirds of their total lipids. Membrane lipids (phospholipids) are important in temperature acclimation of ectotherms. Hence, we experimentally investigated ocean warming and acidification effects on total lipids, lipid classes and fatty acids of Arctic early-stage \textit{L. helicina}. Temperature and pCO\textsubscript{2} treatments chosen resembled Representative Concentration Pathway model scenarios for this century. We found a massive decrease of total lipids at elevated temperature and at the highest CO\textsubscript{2} concentration (1100 $\mu$atm) of the \textit{in situ} temperature. Clearly, temperature was the overriding factor. Total lipids were reduced by 47--70\%, mainly caused by a reduction of phospholipids by up to 60\%. Further, based on pH\textsubscript{T} development in the incubation water of pteropods during the experiment, some evidence exists for metabolic downregulation (shutdown?) in pteropods at high factor levels of temperature and pCO\textsubscript{2}. Consequently, cell differentiation and energy balance of early-stage larvae was probably severely compromised. Comparison of our experimental with 'wild' organisms suggests phospholipid reduction to values clearly outside natural variability. Based on the well-known significance of phospholipids for membranogenesis, early development, and reproduction, negative warming effects on such a basal metabolic function may be a much more immediate threat for pteropods than so far anticipated shell dissolution effects due to acidification.