What we do in the dark: Prevalence of omnivorous feeding activity in Arctic zooplankton during polar night

Abstract

During the productive polar day, zooplankton and sea‐ice amphipods fulfill a critical role in energy transfer from primary producers to higher trophic‐level species in Arctic marine ecosystems. Recent polar night studies on zooplankton and sea‐ice amphipods suggest higher levels of biological activity than previously assumed. However, it is unknown if these invertebrates maintain polar night activity on stored lipids, opportunistic feeding, or a combination of both. To assess how zooplankton (copepods, amphipods, and krill) and sea‐ice amphipods support themselves on seasonally varying resources, we studied their lipid classes, fatty acid compositions, and compound‐specific stable isotopes of trophic biomarker fatty acids during polar day (June/July) and polar night (January). Lipid storage and fatty acid results confirm previously described dietary sources in all species during polar day. We found evidence of polar night feeding in all species, including shifts from herbivory to omnivory. Sympagic‐, pelagic‐, and Calanus spp.‐derived carbon sources supported zooplankton and sea‐ice amphipods in both seasons. We provide a first indication of polar night feeding of sea‐ice amphipods in the pelagic realm.

DNA metabarcoding reveals a diverse, omnivorous diet of Arctic amphipods during the polar night, with jellyfish and fish as major prey

“…The elevated proportion of macroalgae observed in the current study may be caused by the degradation of macrophytes during this season, which makes the material more usable for mesograzers, compared to that of alive macroalgae (Duggins and Eckman, 1997;Hop et al, 2002;Quijoń et al, 2008). Correspondingly, the high-arctic pack-ice species Gammarus wilkitzkii Birula, 1897, exhibits a carnivorousomnivorous feeding throughout the year (Poltermann, 2001;Arndt, 2002;Kunisch et al, 2023). However, the feeding habits of G. wilkitzkii vary on spatial and temporal scales.…”

“…We found both metazoans and macroalgae to be part of the diet of all investigated amphipod species. The presence of a combination of metazoan and macroalgal DNA in the stomachs of the scavenging lysianassoids underlines that omnivory might be common among a large variety of taxa during the Arctic polar night (Kunisch et al, 2023). The two scavenger species exhibited a broader food spectrum than the gammarids.…”

“…Some amphipod and copepod species reduce their feeding rate or overwinter in a state of arrested development, referred to as diapause, relying on lipid storage (Hagen, 1999;Hagen and Auel, 2001;Auel et al, 2002). Recently, it has been shown that some crustacean zooplankton taxa such as under-ice amphipods switch to an omnivorous feeding mode, increasing their feeding flexibility (Kunisch et al, 2023).…”

Zooplankton fecal pellet flux drives the biological carbon pump during the winter–spring transition in a high‐Arctic system

“…Then, we can hypothesize that microzooplankton, mesozooplankton, and euphausiid grazers were feeding and controlled a developing but still moderate phytoplankton production near the surface, preventing it from sinking to the depth of the moored fluorescence sensor. Furthermore, even species considered as primarily herbivorous, such as Calanus spp., and the krill Thysanoessa inermis, have flexible feeding strategies, switching to carnivory when microalgae become scarce (Kleppel 1993;Kunisch et al 2023). Alternative food sources may include ciliates and heterotrophic protists (e.g., Nejstgaard et al 1997;Levinsen et al 2000;Campbell et al 2009), as well as copepods eggs and nauplii (Basedow and Tande, 2006), which all can be abundant prior to the spring bloom in Svalbard fjords (Seuthe et al, 2011;Grenvald et al 2016;Barth-Jensen et al 2022).…”