Winter Carnivory and Diapause Counteract the Reliance on Ice Algae by Barents Sea Zooplankton

• Published in: Frontiers in Marine Science
• Main Authors: Kohlbach, D, Schmidt, K, Hop, H, Wold, A, Al-Habahbeh, AK, Belt, ST, Woll, M, Graeve, M, Smik, L, Atkinson, A, Assmy, P
• Format: Article in Journal/Newspaper
• Language: English
• Published: Frontiers Media SA 2021
• Subjects: Calanus; Themisto; Barents Sea; sea ice; carbon sources; trophic markers; polar night; Calanus glacialis; ice algae; Sea ice; Themisto libellula; Copepods
• Online Access: http://hdl.handle.net/10026.1/16975; https://doi.org/10.3389/fmars.2021.640050

<jats:p>The Barents Sea is a hotspot for environmental change due to its rapid warming, and information on dietary preferences of zooplankton is crucial to better understand the impacts of these changes on food-web dynamics. We combined lipid-based trophic marker approaches, namely analysis of fatty acids (FAs), highly branched isoprenoids (HBIs) and sterols, to compare late summer (August) and early winter (November/December) feeding of key Barents Sea zooplankters; the copepods <jats:italic>Calanus glacialis</jats:italic>, <jats:italic>C. hyperboreus</jats:italic> and <jats:italic>C. finmarchicus</jats:italic> and the amphipods <jats:italic>Themisto libellula</jats:italic> and <jats:italic>T. abyssorum</jats:italic>. Based on FAs, copepods showed a stronger reliance on a diatom-based diet. Phytosterols, produced mainly by diatoms, declined from summer to winter in <jats:italic>C. glacialis</jats:italic> and <jats:italic>C. hyperboreus</jats:italic>, indicating the strong direct linkage of their feeding to primary production. By contrast, <jats:italic>C. finmarchicus</jats:italic> showed evidence of year-round feeding, indicated by the higher winter carnivory FA ratios of 18:1(n-9)/18:1(n-7) than its larger congeners. This, plus differences in seasonal lipid dynamics, suggests varied overwintering strategies among the copepods; namely diapause in <jats:italic>C. glacialis</jats:italic> and <jats:italic>C. hyperboreus</jats:italic> and continued feeding activity in <jats:italic>C. finmarchicus</jats:italic>. Based on the absence of sea ice algae-associated HBIs (IP<jats:sub>25</jats:sub> and IPSO<jats:sub>25</jats:sub>) in the three copepod species during both seasons, their carbon sources were likely primarily of pelagic origin. In both amphipods, increased FA carnivory ratios during winter indicated that they relied strongly on heterotrophic prey ...