Lipids and fatty acids in Clione limacina and Limacina helicina in Svalbard waters and the Arctic Ocean: trophic implications
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Lipid class and fatty acid compositions were determined in Limacina helicina and Clione limacina from an Arctic fjord and the marginal ice zone around Svalbard. C. limacina had higher levels of neutral lipids, including both alkyldiacylglycerols (ADG) and triacylglycerols (TAG), than L. helicina, which contained mainly TAG. However, considerable heterogeneity in the lipid classes and their fatty acids/alcohols were observed in C. limacina in that only two out of the seven specimens analysed were lipid-rich and contained both ADG and TAG, the others having only low percentages of TAG. In specimens of C. limacina containing ADG, 15:0 and 17:1n-8 were prominent fatty acids in both ADG and TAG. The fatty acids of the TAG of L. helicina were variable but 15:0 and 17:1n-8 were absent. We consider the heterogeneity in the fatty acid compositions of L. helicina to reflect temporal and spatial variability in the animals' predominantly phytoplanktonic and particulate diet, which occasionally includes small copepods. We further consider L. helicina to be the prime food for C. limacina and the noticeable amounts of 22:1 found in one sample of C. limacina to reflect significant input of Calanus either directly or indirectly through their prime food, L. helicina. We view the heterogeneity in the fatty acid compositions of both L. helicina and C. limacina, as well as the ability of C. limacina to biosynthesise WE, ADG, 15:0, and 17:1n-8, as adaptations to a large variation of food availability that enables C. limacina to synthesise lipids rapidly and flexibly. Thus, the lipid biochemistry of C. limacina is important in enabling the species to thrive in strong pulses in polar systems.
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