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The reduction of Arctic summer sea ice due to climate change can lead to increased primary production in parts of the Barents Sea if sufficient nutrients are available. Changes in the timing and magnitude of primary production may have cascading consequences for the zooplankton community and ultimately for higher trophic levels. In Arctic food webs, both small and large copepods are commonly present, but may have different life history strategies and hence different responses to environmental change. We investigated how contrasting summer sea-ice cover and water masses in the northern Barents Sea influenced the copepod community composition and secondary production of small and large copepods along a transect from 76°N to 83°N in August 2018 and August 2019. Bulk abundance, biomass, and secondary production of the total copepod community did not differ significantly between the two years. There were however significant spatial differences in the copepod community composition and production, with declining copepod abundance from Atlantic to Arctic waters and the highest copepod biomass and production on the Barents Sea shelf. The boreal Calanus finmarchicus showed higher abundance, biomass, and secondary production in the year with less sea-ice cover and at locations with a clear Atlantic water signal. Significant differences in the copepod community between areas in the two years could be attributed to interannual differences in sea-ice cover and Atlantic water inflow. Small copepods contributed more to secondary production in areas with no or little sea ice and their production was positively correlated to water temperature and ciliate abundance. Large copepods contributed more to secondary production in areas with extensive sea ice and their production was positively correlated with chlorophyll a concentration. Our results show how pelagic communities might function in a future ice-free Barents Sea, in which the main component of the communities are smaller-sized copepod species (including smaller-sized Calanus and small copepods), and the secondary production they generate is available in energetically less resource-rich portions. [ABSTRACT FROM AUTHOR]

During a midwinter cruise north of 80°N to Rijpfjorden, Svalbard, the composition and vertical distribution of the zooplankton community were studied using two different samplers 1) a vertically hauled multiple plankton sampler (MPS; mouth area 0.25 m2, mesh size 200 μm) and 2) a horizontally towed Methot Isaacs Kidd trawl (MIK; mouth area 3.14 m2, mesh size 1500 μm). Our results revealed substantially higher species diversity (49 taxa) than if a single sampler (MPS: 38 taxa, MIK: 28) had been used. The youngest stage present (CIII) of Calanus spp. (including C. finmarchicus and C. glacialis) was sampled exclusively by the MPS, and the frequency of CIV copepodites in MPS was double that than in MIK samples. In contrast, catches of the CV-CVI copepodites of Calanus spp. were substantially higher in the MIK samples (3-fold and 5-fold higher for adult males and females, respectively). The MIK sampling clearly showed that the highest abundances of all three Thysanoessa spp. were in the upper layers, although there was a tendency for the larger-sized euphausiids to occur deeper. Consistent patterns for the vertical distributions of the large zooplankters (e.g. ctenophores, euphausiids) collected by the MPS and MIK samplers provided more complete data on their abundances and sizes than obtained by the single net. Possible mechanisms contributing to the observed patterns of distribution, e.g. high abundances of both Calanus spp. and their predators (ctenophores and chaetognaths) in the upper water layers during midwinter are discussed.

Global warming causes dramatic environmental change to Arctic ecosystems. While pelagic primary production is initiated earlier and its intensity can be increased due to earlier ice melt and extended open‐water periods, sea‐ice primary production is progressively confined on a spatio‐temporal scale, leading to unknown consequences for the ice‐associated (sympagic) food web. Understanding ecological responses to changes in the availability and composition of pelagic and sympagic food sources is crucial to determine potential changes of food‐web structure and functioning in Arctic marine communities under increasingly ice‐free conditions. Focus was placed on the importance of suspended particulate organic matter vs. sympagic organic matter for 12 zooplankton species with different feeding modes covering five taxonomic groups (copepods, krill, amphipods, chaetognaths, and appendicularians) at two ice‐covered, but environmentally different, stations in the north‐western Barents Sea in August 2019. Contributions of diatom‐ and flagellate‐associated fatty acids (FAs) to total lipid content and carbon stable isotopic compositions of these FAs were used to discriminate food sources and trace flows of organic matter in marine food webs. Combination of proportional contributions of FA markers with FA isotopic composition indicated that consumers mostly relied, directly (herbivorous species), or indirectly (omnivorous and carnivorous species), on pelagic diatoms and flagellates, independently of environmental conditions at the sampling locations, trophic position, and feeding mode. Differences were nevertheless observed between species. Contrary to other studies demonstrating a high importance of sympagic organic matter for food‐web processes, our results highlight the complexity and variability of trophic structures and dependencies in different Arctic food webs. [ABSTRACT FROM AUTHOR]

The timing of reproductive events of Calanus glacialis is closely coupled to the two major marine primary production events in the Arctic: the ice algal and phytoplankton blooms. Reproductive strategies vary between different physical and biological environments of the European and Canadian Arctic. In the Canadian Beaufort Sea and the high Arctic Rijpfjorden on Svalbard, C. glacialis utilized the ice algae bloom to fuel spawning in spring, while growth and development of the new generation was primarily supported by the phytoplankton bloom. In the predominantly ice-free Arctic Kongsfjorden (Svalbard), C. glacialis was mainly a capital breeder spawning early in the season in the absence of food. This enabled the offspring to synchronize their growth and development with the phytoplankton bloom and, thus, reproduce successfully despite the lack of an early ice algal bloom. The variability in life history traits observed in the Canadian and European Arctic is compared with data from other Arctic regions to present a pan-Arctic perspective on life cycle strategies of C. glacialis. La chronologie des evenements de reproduction de Calanus glacialis est etroitement liee a deux evenements majeurs touchant a la production primaire marine dans l'Arctique, soit les proliferations d'algues de glace et de phytoplancton. Les strategies de reproduction varient selon les milieux physiques et biologiques dans l'Arctique europeen et canadien. Dans la mer de Beaufort canadienne et dans la region de Rijpfjorden de Svalbard, dans l'Extreme Arctique europeen, C. glacialis tire l'energie necessaire a son frai printanier de la proliferation d'algues de glace, alors que la croissance et le developpement de la nouvelle generation s'appuient principalement sur la proliferation de phytoplancton. Dans la region arctique de Kongsfjorden (Svalbard), exempte de glace en bonne partie, C. glacialis est principalement un reproducteur sur capital qui fraye au debut de la saison en l'absence de nourriture. Cela permet a sa progeniture de synchroniser sa croissance et son developpement avec la proliferation de phytoplancton, ce qui en assure le succes de reproduction malgre l'absence d'une proliferation hative d'algues de glace. La variabilite des caracteristiques du cycle biologique observee dans l'Arctique canadien et europeen est comparee a des donnees pour d'autres regions arctiques afin de brosser un portrait pan-arctique des strategies associees au cycle de vie de C. glacialis. [Traduit par la Redaction], Introduction Copepods of the genus Calanus are key species in the pelagic ecosystems of the Arctic seas (Jaschnov 1970; Conover 1988; Falk-Petersen et al. 2002). They convert low-energy carbohydrates and [...]