Lipid composition of the three co-existing Calanus species in the Arctic: impact of season, location and environment

Arctic species of Calanus are critical to energy transfer between higher and lower trophic levels and their relative abundance, and lipid content is influenced by the alternation of cold and warm years. All three species of Calanus were collected during different periods in Kongsfjorden (Svalbard, 79A degrees N) and adjacent shelf during the abnormally warm year of 2006. Lipid composition and fatty acid structure of individual lipid classes were examined in relation with population structure. Wax esters dominated the neutral lipid fraction. Phosphatidylcholine (PC) dominated the structural lipids followed by phosphatidylethanolamine (PE). PC/PE ratios of 3-6 suggested an increase in PC proportions compared to earlier studies. Depending on the time scale, fatty acids of wax esters illustrated either trophic differences between fjord and offshore conditions for C. hyperboreus and C. finmarchicus or trophic differences related to seasonality for C. glacialis. Similarly, seasonality and trophic conditions controlled the changes in fatty acids of triglycerides, but de novo synthesis of long-chain monoenes suggested energy optimization to cope with immediate metabolic needs. Polar lipids fatty acid composition was species specific and on the long-term (comparison with data from the past decade) composition appears related to changes in trophic environment. Fatty acid composition of PC and PE indicated relative dominance of 20:5n-3 in PC and 22:6n-3 in PE for all three species. The combination of PE and PC acyl chain and phospholipid head group restructuring indicates an inter-annual variability and suggests that membrane lipids are the most likely candidate to evaluate adaptive changes in Arctic copepods to hydrothermal regime.