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Summary Zooplankton inhabiting the Hornsund and Kongsfjorden fjords on Spitsbergen (Svalbard) were investigated in summer 2013. The goal of the study was to determine how the zooplankton communities vary in environments functioning under different oceanographic regimes. Sampling was conducted with nets of different mesh size and selectivity (56 μm WP-2, 180 μm MultiNet, and 1000 μm Tucker Trawl), which permitted comparing a wide size spectrum of zooplankton components. Species composition did not differ substantially between the fjords, but the zooplankton in Hornsund was almost two times less numerous, and it had lower biomass per unit volume. The highest abundance at both sites was in the smallest zooplankton size fraction found only in samples taken with 56 μm mesh WP-2 net. These comprised as much as 71% and 58% of the total zooplankton abundance in Hornsund and Kongsfjorden, respectively. The communities in both fjords had comparable contributions of Arctic and boreo-Arctic species biomass in the year of the study. However, the comparison of zooplankton characteristics over several years showed changes in abundance and biogeographic structure that corresponded with variations in the physical environments of the fjords. The results of the study permit predicting the possible effects of the increasing influence of Atlantic waters on zooplankton communities inhabiting Arctic marine pelagic ecosystems.

Source at https://doi.org/10.3389/fmars.2019.00293. The Arctic Ocean is changing rapidly with respect to ice cover extent and volume, growth season duration and biological production. Zooplankton are important components in the arctic marine food web, and tightly coupled to the strong seasonality in primary production. In this study, we investigate zooplankton composition, including microzooplankton, copepod nauplii, as well as small and large copepod taxa, and primary productivity in the dynamic Atlantic water inflow area north of Svalbard in May and August 2014. We focus on seasonal differences in the zooplankton community and in primary productivity regimes. More specifically, we examine how a shift from “new” (nitrate based) spring bloom to a “regenerated” (ammonium based) post bloom primary production is reflected in the diversity, life history adaptations and productivity of the dominant zooplankton. North of Svalbard, the seasonal differences in planktonic communities were significant. In spring, the large copepod Calanus finmarchicus dominated, but the estimated production and ingestion rates were low compared to the total primary production. In summer, the zooplankton community was composed of microzooplankton and the small copepod Oithona similis. The zooplankton production and ingestion rates were high in summer, and probably depended heavily on the regenerated primary production associated with the microbial loop. There was clear alteration from dominance of calanoid copepod nauplii in spring to Oithona spp. nauplii in summer, which indicates different reproductive strategies of the dominating large and small copepod species. Our study confirms the dependence and tight coupling between the new (spring bloom) primary production and reproductive adaptations of C. glacialis and C. hyperboreus. In contrast, C. finmarchicus appears able to take advantage of the regenerated summer primary production, which allows it to reach the overwintering stage within one growth season in this region north of Svalbard. This suggests that C. finmarchicus will be able to profit from the predicted increased primary production in the Arctic, a strategy also recognized in small copepod species such as O. similis. We speculate that the ability of the copepod species to utilize the regenerated summer primary production and microbial food web may determine the winners and losers in the future Arctic Ocean.

Summary This paper presents information on diet and distribution of larval snailfishes from the genus Liparis on the Canadian Beaufort Sea Shelf. In this study, 153 larval snailfishes of three species, Liparis fabricii, L. gibbus and L. tunicatus, were collected during 4 summer cruises (2003–2005, 2007). The majority of the larvae were either in flexion or post-flexion stage, and some were in pre-flexion stage. Liparis larvae appeared to be generalists in terms of diet and fed on a wide range of planktonic organisms. Pre-flexion larvae fed on small copepods (mainly adult stages of Triconia borealis). As larvae grew their diet shifted towards larger copepods (copepodids III/IV of Calanus hyperboreus, copepodids II–IV of Calanus glacialis and females of Metridia longa) and amphipods (Themisto libellula). Remarkably, larvaceans Oikopleura spp. and pelagic snails Limacina helicina made up a substantial part of the larval diet. This paper contributes to the knowledge on arctic larval fishes and to the ongoing efforts regarding Canadian Beaufort Sea ecosystem modeling.

The advection of warm Atlantic water into the Arctic influences not only the thermal and sea ice conditions in the Arctic Ocean and the adjacent seas but also the Arctic marine biota. Earlier efforts to characterize the response of zooplankton communities to the increasing influence of warm AW were focused mostly on changes in taxonomic diversity and community structure, but how the zooplankton functional role will evolve under future global warming scenarios remains largely unknown. Based on the zooplankton collection gathered along a thermal gradient from temperate to Arctic marine domains (76-79°N) and an extensive functional trait matrix, we assessed the zooplankton taxonomical and functional structure and diversity under different temperature regimes. The results suggest that the temperature effects zooplankton community structure, taking into account not only the taxonomic, but also functional features. The findings can be used in predicting changes in the pelagic realm in the warming Arctic Ocean, and in constructing and tuning plankton components of ecosystem models.

International audience; The Arctic icescape is rapidly transforming from a thicker multiyear ice cover to a thinner and largely seasonal first-year ice cover with significant consequences for Arctic primary production. One critical challenge is to understand how productivity will change within the next decades. Recent studies have reported extensive phytoplankton blooms beneath ponded sea ice during summer, indicating that satellite-based Arctic annual primary production estimates may be significantly underestimated. Here we present a unique time-series of a phytoplankton spring bloom observed beneath snow-covered Arctic pack ice. The bloom, dominated by the haptophyte algae Phaeocystis pouchetii, caused near depletion of the surface nitrate inventory and a decline in dissolved inorganic carbon by 16 ± 6 g C m−2. Ocean circulation characteristics in the area indicated that the bloom developed in situ despite the snow-covered sea ice. Leads in the dynamic ice cover provided added sunlight necessary to initiate and sustain the bloom. Phytoplankton blooms beneath snow-covered ice might become more common and widespread in the future Arctic Ocean with frequent lead formation due to thinner and more dynamic sea ice despite projected increases in high-Arctic snowfall. This could alter productivity, marine food webs and carbon sequestration in the Arctic Ocean. Annual phytoplankton net primary production in the Arctic Ocean has increased by 30% since the late 1990's mainly due to the declining sea ice extent and an increasing phytoplankton growth season 1. However, there is considerable uncertainty about the future change in Arctic Ocean primary productivity largely attributed to the

A multi-scale approach was used to evaluate which spatial gradient of environmental variability is the most important in structuring zooplankton diversity in the West Spitsbergen Current (WSC). The WSC is the main conveyor of warm and biologically rich Atlantic water to the Arctic Ocean through the Fram Strait. The data set included 85 stratified vertical zooplankton samples (obtained from depths up to 1000 metres) covering two latitudinal sections (76°30’N and 79°N) located across the multi-path WSC system. The results indicate that the most important environmental variables shaping the zooplankton structural and functional diversity and standing stock variability are those associated with depth, whereas variables acting in the horizontal dimension are of lesser importance. Multivariate analysis of the zooplankton assemblages, together with different univariate descriptors of zooplankton diversity, clearly illustrated the segregation of zooplankton taxa in the vertical plane. The epipelagic zone (upper 200 m) hosted plentiful, Oithona similis-dominated assemblages with a high proportion of filter-feeding zooplankton. Although total zooplankton abundance declined in the mesopelagic zone (200–1000 m), zooplankton assemblages in that zone were more diverse and more evenly distributed, with high contributions from both herbivorous and carnivorous taxa. The vertical distribution of integrated biomass (mg DW m-2) indicated that the total zooplankton biomass in the epipelagic and mesopelagic zones was comparable. Environmental gradients acting in the horizontal plane, such as the ones associated with different ice cover and timing of the spring bloom, were reflected in the latitudinal variability in protist community structure and probably caused differences in succession in the zooplankton community. High abundances of Calanus finmarchicus in the WSC core branch suggest the existence of mechanisms advantageous for higher productivity or/and responsible for physical concentration of zooplankton. Our results indicate that regional hydrography plays a primary role in shaping zooplankton variability in the WSC on the way to the Arctic Ocean, with additional effects caused by biological factors related to seasonality in pelagic ecosystem development, resulting in regional differences in food availability or biological production between the continental slope and the deep ocean regions.

One of the main challenges in contemporary biological oceanography is to understand the factors that drive the spatial heterogeneity of pelagic organisms. Our study was performed at 10-m depth intervals within the upper 50 m of the ocean, at two different localities on the West Spitsbergen Shelf in the summers of 2009 and 2010. The fine-scale patterns in vertical zooplankton distribution were studied concurrently with measurements of hydrographic and optical properties of the water. We adopted a novel approach to the acquisition of information on light, phytoplankton and particle distributions by in situ measurements with optical sensors. Based on our data, we distinguished specific zooplankton vertical distribution patterns such as the aggregation of Calanus finmarchicus and small copepods toward the surface and the relatively high contribution of C. glacialis to subsurface layers. A vertical separation of Calanus sp. developmental stages was observed, and zones of rather even zooplankton distributions were also found. The variability in zooplankton distribution and community structure was closely related to the hydrographic and optical characteristics of the water; therefore, we hypothesize that these patterns could be the result of fine-scale microhabitat selection by different zooplankton species and life stages.

We studied summer mesozooplankton composition between 2001 and 2009, in the epipelagic zone of the West Spitsbergen Current (WSC) and adjacent areas, which constitute a transition zone between warmer Atlantic and cold Arctic waters. According to hydrography and species composition, this region could be divided into 4 main areas: western and eastern branches of the WSC, the Greenland Sea together with Fram Strait, and the shelf areas of Spitsbergen and the Barents Sea. The most abundant species was Oithona similis and the most important, in terms of biomass, was Calanus finmarchicus; both species were found at all stations. The novel spatial analysis method of principal coordinates of neighbour matrices (PCNM) and the following variation partitioning were applied to disentangle the contributions of environmental variables and spatial differences in explaining mesozooplankton community variation. In spite of the large geographic area covered, environmental factors used in redundancy analysis (RDA) explained 30.6% of zooplankton variability, while the spatial distribution of sampling stations was responsible for 27.2%, and 12.5% was a common share of both predictors, coming from their correlations. We observed a smooth change from dominance of ubiquitous and boreo-Arctic taxa such as O. similis and Triconia sp. in the beginning of the study period towards stronger dominance of boreal taxa such as C. finmarchicus, which was the most abundant species in 2009.

This paper contributes to baseline knowledge of lower trophic levels that is necessary to monitor the impact of oil and gas development on the Canadian Beaufort Sea ecosystem. As part of the Nahidik Program, the vertical distribution of mesozooplankton was studied along two transects in the coastal Canadian Beaufort Sea in the summer of 2009. Mesozooplankton was collected with 153 μm conical net in two hydrologically distinct layers – the upper layer which was fresher and warmer due to the Mackenzie River runoff, and the lower layer which was colder and more saline. Two separate mesozooplankton assemblages were distinguished in the individual layers. The average zooplankton abundance in the two layers was 3120 ± 2860 ind. m − 3 and 4200 ± 5550 ind. m − 3 in the upper and lower layer, respectively. The upper layer was largely inhabited by meroplanktonic Polychaeta (752 ± 1038 ind. m − 3 ) and Bivalvia larvae (228 ± 307 ind. m − 3 ) as well as by youngest stages of Pseudocalanus spp. (245 ± 499 ind. m − 3 ). Conversely, the lower layer was mainly occupied by typical marine taxa such as Calanus glacialis (95 ± 76 ind. m − 3 ), C. hyperboreus (27 ± 12 ind. m − 3 ) and Triconia borealis (111 ± 81 ind. m − 3 ). Oithona similis , a widely distributed eurytopic cyclopoid copepod, showed no consistent pattern of vertical distribution (280 and 291 ind. m − 3 , in the lower and upper layer, respectively).

The Arctic Ocean is facing rapid changes in seawater carbonate chemistry due to the uptake of atmospheric carbon dioxide (CO 2 ). In the current study, the effects of different seawater pH levels (8.2, 7.6 and 6.9) on the reproduction of Calanus glacialis , an Arctic shelf-water copepod, have been quantified. Results indicated that CO 2 -induced seawater acidification had no significant effect on C. glacialis egg production. However, a reduction in pH to 6.9 significantly delayed hatching and possibly reduced overall hatching success. The results of the current study are in agreement with previous studies on other copepod species and would indicate that copepods, as a group, may be well equipped to deal with the chemical changes associated with ocean acidification. However, all previous studies have been over relatively short exposure periods and most have only considered the isolated impacts of elevated CO 2 . Long-term exposures examining the synergistic effects of ocean acidification with other climate stressors, particularly warming on population viability and success, have yet to be conducted.

Kwasniewski, S., Gluchowska, M., Walkusz, W., Karnovsky, N. J., Jakubas, D., Wojczulanis-Jakubas, K., Harding, A. M. A., Goszczko, I., Cisek, M., Beszczynska-Möller, A., Walczowski, W., Weslawski, J. M., and Stempniewicz, L. 2012. Interannual changes in zooplankton on the West Spitsbergen Shelf in relation to hydrography and their consequences for the diet of planktivorous seabirds. – ICES Journal of Marine Science, 69: 890–901. The purpose of the work was to determine how atmospheric and oceanic processes (the North Atlantic Oscillation (NAO) and the Arctic Ocean Oscillation (AOO)) influence hydrography and zooplankton on the West Spitsbergen Shelf (WSS), and the impacts of the processes on chick meals of zooplanktivorous little auks Alle alle. There were distinct Atlantic and Arctic oceanographic domains on the shelf resulting from the presence of the West Spitsbergen Current and the Sørkapp Current, which contain different proportions of Calanus finmarchicus and C. glacialis. The abundance of warm- and cold-water species varied as a result of an interplay between processes in the atmosphere and ocean. In the Arctic domain, on which the study focused, the NAO impacted oceanography, zooplankton, and consequently little auk chick meals, with time-lags of 4–7 years. The diet of little auk chicks was more energy-rich when C. glacialis stage 5 in the Arctic community were more easily available. To date, the changes in zooplankton abundance on the WSS have not posed a threat to the ability of little auks to feed their chicks lipid-rich Arctic copepods.

Composition and abundance of zooplankton were studied simultaneously with feeding ecology of planktivorous Little Auks (Alle alle) in two different sea shelf areas of West Spitsbergen, Norway, in summer 2007. Zooplankton was collected adjacent to bird colonies in Magdalenefjorden (influenced by Atlantic West Spitsbergen Current) and Hornsund (dominated by the Arctic Sorkapp Current). In spite of different hydrological situations, the abundance of prey preferred by Little Auks, Arctic Calanus glacialis copepodids stage V, among zooplankton was similar in both localities. However, there was much more of Atlantic Calanus finmarchicus on the shelf outside Magdalenefjorden compared to Hornsund, resulting in different abundance ratios of Arctic to Atlantic copepods in the two areas (1:14 and 1:1, respectively). Even greater differences between the two areas occurred in the ratio of C. glacialis CV to other zooplankters, amounting to 1:40 in Magdalenefjorden and 1:6 in Hornsund. In both Little Auk colonies food brought by parents to their chicks contained mainly C. glacialis CV, albeit the proportion of this copepod in meals was significantly higher in Hornsund. Meals delivered to Little Auk chicks in Hornsund had also higher zooplankton numbers, biomass and energy content. In Magdalenefjorden, on the other hand, a higher number of feedings and longer duration of foraging trips were recorded. These differences became more apparent with increasing energy requirements of the fast growing nestlings. This was probably a consequence of lower relative abundance of the Little Auks’ preferred prey in the sea adjacent to Magdalenefjorden colony. It seems that searching for the preferred food items, such as C. glacialis, among abundant but less favored C. finmarchicus, may require more time and energy demanding foraging behavior. As a consequence, foraging effort of the Little Auk parents from Magdalenefjorden was higher, and feeding efficiency lower, than those of birds from Hornsund. Increasing influx of warm Atlantic waters that bring boreal zooplankton to the Arctic Seas may have negative impacts on Little Auks’ time and energy budgets and eventually on their breeding success and range of breeding distribution.

The lipid class compositions of the ctenophores Mertensia ovum and Beroe cucumis were very similar, with polar lipid and wax esters each accounting for 35 to 40% of the total. The fatty acid compositions of the polar lipids in the 2 species were essentially the same, with 22:6n3 and 20:5n3 in a ratio of 2:1 accounting for more than 40% of the total. The fatty acid and fatty alcohol com- positions of the wax esters of both species were also essentially the same, with 20:1n9 and 22:1n11 fatty alcohols present in equal amounts accounting for 60% of the total fatty alcohol composition. The fatty acid and fatty alcohol compositions of the wax esters of M. ovum and B. cucumis were averaged and compared, using principal component analyses, to averages derived from published data for the potential prey species: Calanus finmarchicus, C. glacialis, C. hyperboreus, Pseudocalanus acuspes, Acartia longiremis and Metridia longa. The results were consistent with Calanus spp., especially C. glacialis, being the major prey of M. ovum and with M. ovum being the major prey of B. cucumis.

The percentage (%) fatty alcohol and fatty acid compositions of the wax esters of large numbers of Stage V and females of Calanus hyperboreus, C. glacialis and C. finmarchicus taken in late August to late September from Arctic waters (Kongsfjord in Svalbard, 78° 57' N, 11° 50' E) are presented. The data reveal that these stages of development of the 3 species can be discriminated on the basis of the % of 22:1n-11 fatty alcohol in their large levels of wax esters, with C. hyperboreus having the highest % followed by C. finmarchicus and then C. glacialis. Equally, C. hyperboreus has the lowest % of 20:1n-9 fatty alcohol in its wax esters with C. finmarchicus having a higher % and C. glacialis the highest %. Relatively minor differences occur in the fatty acid compositions of the wax esters of the 3 species, which consisted principally of 20:1n-9 (15 to 18%) and 22:1n-11 (10 to 15%), together with the diatom-derived fatty acids 16:1n-7 (20 to 23%) and 20:5n-3 (11 to 13%). The flagellate-derived fatty acids, 18:4n-3 (3 to 6%) and 22:6n-3 (1 to 3%), were minor constituents. The fatty acid compositions of the small amounts of polar lipid in the 3 species were indistinguishable with 22:6n-3 (41 to 46%) and 20:5n-3 (22 to 24%) being the major components. We conclude that Stage V and females of the species can be distinguished in autumn on the basis of the different % of 22:1n-11 and 20:1n-9 fatty alcohols in their wax esters and that de novo lipid biosynthetic activity in the cope- pods increases in the order C. finmarchicus < C. glacialis < C. hyperboreus. We discuss the results in terms of the contributions of fatty acids and fatty alcohols biosynthesised de novo and fatty acids derived from the diet to the copepods' lipids, the role of 20:1 and 22:1 fatty alcohols and fatty acids as energy sources, and the possible role of 22:6n-3 in the copepods' physiology.

The complete diet composition structure of the most numerous planktivorous sea bird, little auk (Alle alle), in the European Arctic, is still not fully recognized. Although regular constituents of little auk chick diets, the copepods, Calanus glacialis and C. finmarchicus have been previously relatively well described, more taxa were frequent ingredients of the bird’s meals. Therefore, the role of the little auks supplementary diet components (SDCs) at two colonies in the Svalbard Archipelago, Hornsund and Magdalenefjorden, in 2007–2009, is a main subject of this comparative study. Because the SDCs often consisted of scarce but large zooplankters, this investigation was focused on biomass as a proxy of the SDCs’ energy input. Although the total biomass of the food delivered to chicks in both colonies was similar, in Magdalenefjorden, the proportion of SDCs was twice that found in Hornsund. The main SDCs in Hornsund were Decapoda larvae (with predominating Pagurus pubescens) and Thysanoessa inermis, whereas the main SDCs in Magdalenefjorden were C. hyperboreus and Apherusa glacialis. Previous investigations, which indicated lipid richness of SDCs, together with our ecological results from the colonies, suggest that this category might play a compensatory role in little auk chick diets. The ability to forage on diverse taxa may help the birds to adapt to ongoing Arctic ecosystem changes.

Lipid class and fatty acid compositions were determined in Limacina helicina and Clione limacina from an Arctic fjord and the marginal ice zone around Svalbard. C. limacina had higher levels of neutral lipids, including both alkyldiacylglycerols (ADG) and triacylglycerols (TAG), than L. helicina, which contained mainly TAG. However, considerable heterogeneity in the lipid classes and their fatty acids/alcohols were observed in C. limacina in that only two out of the seven specimens analysed were lipid-rich and contained both ADG and TAG, the others having only low percentages of TAG. In specimens of C. limacina containing ADG, 15:0 and 17:1n-8 were prominent fatty acids in both ADG and TAG. The fatty acids of the TAG of L. helicina were variable but 15:0 and 17:1n-8 were absent. We consider the heterogeneity in the fatty acid compositions of L. helicina to reflect temporal and spatial variability in the animals' predominantly phytoplanktonic and particulate diet, which occasionally includes small copepods. We further consider L. helicina to be the prime food for C. limacina and the noticeable amounts of 22:1 found in one sample of C. limacina to reflect significant input of Calanus either directly or indirectly through their prime food, L. helicina. We view the heterogeneity in the fatty acid compositions of both L. helicina and C. limacina, as well as the ability of C. limacina to biosynthesise WE, ADG, 15:0, and 17:1n-8, as adaptations to a large variation of food availability that enables C. limacina to synthesise lipids rapidly and flexibly. Thus, the lipid biochemistry of C. limacina is important in enabling the species to thrive in strong pulses in polar systems.