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A research on renewal rate, allocation and bioconverting capabilities of fatty acids in P.quadrispinosa.

Shortening winters and changing ice and snow cover conditions are examples of the many shifts expected in subarctic lakes due to climate change. Well-documented changes in ice and snow cover conditions highlight the need to understand under-ice ecosystems and the consequences a changing climate brings to the freshwater biota. This study investigated the impact of under-ice environmental conditions and seasonal progression on the plankton community and lipid dynamics in Takvatn, a well-studied subarctic oligotrophic lake in Northern Norway. In particular, this study focused on two actively overwintering copepods, Cyclops scutifer, and Eudiaptomus graciloides. The two species differed in their life strategies and fatty acid composition; C. scutifer overwintered in the C-IV to C-V stage, while E. graciloides reproduced under ice-cover. A rapid decrease in lipid content throughout the ice-covered period was observed for both E. graciloides (from 60% to 38% DW-1) and C. scutifer (from 73% to 33% DW-1). The results indicate the importance of lipid accumulation before ice-cover for the actively overwintering copepods to survive the ice-cover period. In addition, under-ice primary production, which was apparent during the last months of ice-cover, provided a food source for E. graciloides. Compared to the previous winter, this winter zooplankton had a higher proportion of lipids to body mass. This suggests the current winter to have favourable conditions and might allow zooplankton to survive harsher/longer periods of ice-cover. Further, E. graciloides had large amounts of poly unsaturated fatty acids (in particular Stearidonic acid, 18:4n-3) which decreased rapidly and might be linked to under-ice reproduction in this species. Future changes in ice-cover duration and snow and ice conditions due to climate change effects may play a significant role in the quantity and quality of lipids of an organism. This study contributes to the understanding of plankton and lipid dynamics during the understudied winter period under ice-cover and provides a reference point for future under-ice studies.

Gammarid amphipods are a crucial link connecting primary producers with secondary consumers, but little is known about their nutritional ecology. Here we asked how starvation and subsequent feeding on different nutritional quality algae influences fatty acid retention, compound-specific isotopic carbon fractionation, and biosynthesis of omega-3 and omega-6 polyunsaturated fatty acids (PUFA) in the relict gammarid amphipod Pallaseopsis quadrispinosa. The fatty acid profiles of P. quadrispinosa closely matched with those of the dietary green algae after only seven days of refeeding, whereas fatty acid patterns of P. quadrispinosa were less consistent with those of the diatom diet. This was mainly due to P. quadrispinosa suffering energy limitation in the diatom treatment which initiated the metabolization of 16:1 omega 7 and partly 18:1 omega 9 for energy, but retained high levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) similar to those found in wild-caught organisms. Moreover, alpha-linolenic acid (ALA) from green algae was mainly stored and not allocated to membranes at high levels nor biosynthesized to EPA. The arachidonic acid (ARA) content in membrane was much lower than EPA and P. quadrispinosa was able to biosynthesize long-chain omega-6 PUFA from linoleic acid (LA). Our experiment revealed that diet quality has a great impact on fatty acid biosynthesis, retention and turnover in this consumer.