Stable isotope labeling reveals patterns in essential fatty acid growth efficiency in a lipid-poor coastal calanoid cope
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ORIGINAL PAPER
Stable isotope labeling reveals patterns in essential fatty acid growth efficiency in a lipid‑poor coastal calanoid copepod Laura Helenius1 · Suzanne M. Budge1 · Catherine L. Johnson2 Received: 1 May 2020 / Accepted: 6 October 2020 © Crown 2020
Abstract Copepods are an important link in marine food webs, transferring crucial nutrients such as essential fatty acids (EFA) from primary producers to higher consumers. Yet data on lipid dynamics in marine ecosystems associated with small lipid-poor copepods are scarce. In this study, we used the coastal calanoid copepod Eurytemora herdmani, which is an opportunistic generalist feeder, to assess EFA-specific gross growth efficiency (GGEEFA), defined as the fraction of ingested EFA retained in copepod tissue. We conducted two eight-day feeding experiments with 13C-labeled phytoplankton to quantify incorporation and GGEEFA of eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA) in stage CV E. herdmani copepodites consuming either the EPA-replete diatom Thalassiosira weissflogii or the DHA-replete mixotrophic dinoflagellate Heterocapsa triquetra. EFA incorporation was quantified using gas chromatography. We recorded rapid shifts (within 48 h) in copepod tissue fatty acid (FA) composition following diet change, but not directly mirroring dietary algal FA. We also found high GGEEFA, with maxima of 46% and 61% for EPA and DHA, respectively, in copepods ingesting T. weissflogii and 39% and 87%, respectively, in copepods ingesting H. triquetra. GGEDHA remained higher than G GEEPA throughout the experiments regardless of dietary algae. G GEEFA decreased overall when copepods matured and produced nauplii, indicating EFA allocation for reproductive purposes. G GEDHA values in non-reproducing E. herdmani copepodites were high, suggesting that under predicted shifts in copepod community size structure, trophic transfer by small copepods could help compensate for DHA reductions resulting from lower abundances of large, lipid-rich species.
Introduction Quantifying the flux of nutrients through marine ecosystems presents a major challenge in food web ecology. One particularly crucial class of nutrients produced at the lowest trophic levels consists of long chain polyunsaturated fatty acids (LC-PUFA), which are critical structural components and precursors to signaling molecules. They are involved in many diverse biological and biochemical processes in all Responsible Editor: C. Meunier. Reviewed by L. Boissonnot and undisclosed experts. * Laura Helenius [email protected] 1
Department of Process Engineering and Applied Science, Dalhousie University, 1360 Barrington Street, Halifax, N.S B3H 4R2, Canada
Fisheries and Oceans Canada, Bedford Institute of Oceanography, 1 Challenger Drive, Dartmouth, N.S B2Y 4A2, Canada
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organisms (Fotuhi et al. 2009). Essential fatty acids (EFA), such as the omega-3 FA eicosapentaenoic acid (EPA, 20:5n3) and docosahexaenoic acid (DHA, 22:6n-3) are needed for successful growth,
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