ALBERT

Description: Our study deals with the lipid biochemistry of the krill community in the ecosystem of the high Arctic Kongsfjord (Svalbard). During the last decades, Kongsfjord experienced a change in krill species composition due to recent increased advection of Atlantic water masses carrying characteristic boreal as well as subtropical-boreal euphausiids into the ecosystem. The lipid biochemistry and trophic relationships of the species recently inhabiting the Arctic water masses are scarcely known, although a change in a krill population may have a significant impact on the ecosystem. A comparison of nutrition and energy storage strategies, stable isotopes, lipid profiles and fatty acid compositions showed remarkable differences between the krill species. These reflected the diverse feeding behaviours and specific adaptations to the environments of their origin: the boreal Meganyctiphanes norvegica and subtropical Nematoscelis megalops appear more carnivorous, have significantly lower mean lipid contents (29 % and 10 %, respectively) and a different energy storage pattern (triacylglycerols and polar lipids, respectively) than the arcto-boreal Thysanoessa inermis, which consists of up to 54 % of lipids mainly stored as wax esters (〉 40 %). These differences may have significant implications for the rapidly changing marine food-web of Kongsfjord - especially for higher trophic levels relying on the nutritional input of animal lipids.

Description: Knowledge on the capability of zooplankton to adapt to the rapidly changing environmental conditions in the Arctic is crucial to predict future ecosystem processes. The key species on the Arctic shelf, the calanoid copepod Calanus glacialis, grows and accumulates lipid reserves in spring and summer in surface waters. The winter is spent in dormancy in deeper water layers with low metabolic activity. As timing and intensity of metabolic changes have been poorly investigated, our study aims to characterize the physiology of C. glacialis over an entire year, from July 2012 to July 2013. We followed anabolic and catabolic enzyme activities and the biochemical composition of this species, taking depth-stratified samples once a month in Billefjorden, a high-Arctic sill fjord. A large part of the population had migrated to depths 〉100 m by July 2012. Only thereafter, anabolic activities decreased slowly, suggesting that low metabolism is related to ceased feeding rather than to endogenous regulation. During overwintering, anabolic enzyme activities were reduced by half as compared to peak activities in spring. The biochemical composition of the copepods changed little from July to December. Then, the lipid catabolic activity increased and the lipid content decreased, likely fuelling moulting and gonad maturation. The protein content did not change significantly during winter, suggesting that proteins are not much catabolized during that time. The relatively high metabolic activity in C. glacialis in winter suggests that this species is not entering a true diapause and should thus be able to respond flexible to changing environmental conditions.