Abstract
The impacts of biochemicals driving food web processes are under investigation for just the last few decades. In addition, as jellyfish are drawing increasing attentions because of their mass developments and of their potential capacity of driving food web structures and energy flow by ‘top-down’ and ‘bottom-up’ controls. We here show that the provision with the biochemical complex thiamin (vitamin B1) to the common phytoplankton Rhodomonas baltica altered its fatty acid (FA) pattern towards 3-highly-unsaturated FAs (3-HUFA) and that this pattern was further transferred up to the zooplankton consumer, the copepod Acartia tonsa. However, polyps of the Jellyfish Aurelia aurita feeding on A. tonsa only had a low relative 3-HUFA content, especially due to a reduction in 22:63 (DHA), but elevated levels of 20:46 (ARA). The high proportion of the -6 HUFA, ARA in polyps may provide evidence for preferential conversion of ARA in polyps, eventually from DHA in a so far unknown pathway. In contrast to A. tonsa, newly hatched A. salina nauplii used as food for A. aurita polyps were almost devoid of HUFA, but contained high levels of C18 polyunsaturated FAs (C18-PUFA). Consequently, polyps feeding on them contained few HUFA, while high levels of C18-PUFA predominated. This suggests that A. aurita polyps cannot efficiently convert 3 C18-PUFA to 3-HUFA. In addition, besides a decrease in saturated FAs, especially an increase in HUFA in A. aurita polyps with decreasing temperature was observed, for which the dietary provision with HUFA seemed to be critical. Altering the FA pattern as a response of temperature reflects an adaptation to seasonal changes and may be related to their life history plasticity.
Highlights
Solar Energy that is fixed by primary producers is transferred to higher trophic levels via predator-prey interactions reallocating biomolecules through metabolic pathways
We found vitamin B1 induced alterations of the fatty acid (FA), especially highly unsaturated FA (HUFA) composition at the primary producer level being transferred to the primary consumer level
Further up the food chain, HUFA of jellyfish polyps were influenced by the diet with similar relative levels for eicosapentaenoic acid (EPA), but strongly reduced docosahexaenoic acid (DHA) levels when feeding on A. tonsa
Summary
Solar Energy that is fixed by primary producers is transferred to higher trophic levels via predator-prey interactions reallocating biomolecules (such as carbohydrates, lipids, proteins and nucleic acids) through metabolic pathways. The syntheses rates of these essential or semi-essential biomolecules and the transfer efficiencies among food chains will determine the trophic structures of food webs and might regulate “bottom-up” control to higher trophic levels (Hairston and Hairston, 1993) These bio-compounds are critically important for organisms’ fitness by regulating their metabolism, growth, and reproduction, and can serve as indicators of dietary. It has been shown that fish larvae require a high level of DHA and arachidonic acids (ARA; 20:4ω6) for optimal growth and survival (Izquierdo, 1996; Sargent et al, 1999; Copeman et al, 2002; Yuan et al, 2015) Likewise, another HUFA, the natural dietary content of EPA, was found to be well related to the growth rate and egg production of the freshwater zooplankton Daphnia (Müller-Navarra, 1995; Müller-Navarra et al, 2000)
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