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Arctic shipping and oil exploration are expected to increase, as sea ice extent is reduced. This enhances the risk for accidental oil spills throughout the Arctic, which emphasises the need to quantify potential consequences to the marine ecosystem and to evaluate risk and choose appropriate remediation methods. This study investigated the sensitivity of Arctic marine plankton to the water accommodated fraction (WAF) of heavy fuel oil. Arctic marine phytoplankton and copepods (Calanus finmarchicus) were exposed to three WAF concentrations corresponding to total hydrocarbon contents of 0.07 mg l -1 , 0.28 mg l -1 and 0.55 mg l -1 . Additionally, the potential phototoxic effects of exposing the WAF to sunlight, including the UV spectrum, were tested. The study determined sub-lethal effects of WAF exposure on rates of key ecosystem processes: primary production of phytoplankton and grazing (faecal pellet production) of copepods. Both phytoplankton and copepods responded negatively to WAF exposure. Biomass specific primary production was reduced by 6, 52 and 73% and faecal pellet production by 18, 51 and 86% with increasing WAF concentrations compared to controls. The phototoxic effect reduced primary production in the two highest WAF concentration treatments by 71 and 91%, respectively. This experiment contributes to the limited knowledge of acute sub-lethal effects of potential oil spills to the Arctic pelagic food web.

Biological clocks are a ubiquitous ancient and adaptive mechanism enabling organisms to anticipate environmental cycles and to regulate behavioral and physiological processes accordingly [1]. Although terrestrial circadian clocks are well understood, knowledge of clocks in marine organisms is still very limited [2-5]. This is particularly true for abundant species displaying large-scale rhythms like diel vertical migration (DVM) that contribute significantly to shaping their respective ecosystems [6]. Here we describe exogenous cycles and endogenous rhythms associated with DVM of the ecologically important and highly abundant planktic copepod Calanus finmarchicus. In the laboratory, C. finmarchicus shows circadian rhythms of DVM, metabolism, and most core circadian clock genes (clock, period1, period2, timeless, cryptochrome2, and clockwork orange). Most of these genes also cycle in animals assessed in the wild, though expression is less rhythmic at depth (50-140 m) relative to shallow-caught animals (0-50 m). Further, peak expressions of clock genes generally occurred at either sunset or sunrise, coinciding with peak migration times. Including one of the first field investigations of clock genes in a marine species [5, 7], this study couples clock gene measurements with laboratory and field data on DVM. While the mechanistic connection remains elusive, our results imply a high degree of causality between clock gene expression and one of the planet's largest daily migrations of biomass. We thus suggest that circadian clocks increase zooplankton fitness by optimizing the temporal trade-off between feeding and predator avoidance, especially when environmental drivers are weak or absent [8]., (Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Diapause plays a key role in the life cycle of high latitude zooplankton. During diapause, animals avoid starving in winter by living in deep waters where metabolism is lower and met by lipid reserves. Global warming is therefore expected to shorten the maximum potential diapause duration by increasing metabolic rates and by reducing body size and lipid reserves. This will alter the phenology of zooplankton, impact higher trophic levels and disrupt biological carbon pumps. Here, we project the impacts of climate change on the key North Atlantic copepod Calanus finmarchicus under IPCC RCP 8.5. Potential diapause duration is modelled in relation to body size and overwintering temperature. The projections show pronounced geographic variations. Potential diapause duration reduces by more than 30% in the Western Atlantic, whereas in the key overwintering centre of the Norwegian Sea it changes only marginally. Surface temperature rises, which reduce body size and lipid reserves, will have a similar impact to deep-water changes on diapause in many regions. Because deep-water warming lags that at the surface, animals in the Labrador Sea could offset warming impacts by diapausing in deeper waters. However, the ability to control diapause depth may be limited., (© 2016 John Wiley & Sons Ltd.)

Understanding how climate influences ecosystems is complicated by the many correlated and interrelated impacting factors. Here we quantify climate effects on Calanus finmarchicus in the northeastern Norwegian Sea and southwestern Barents Sea. By combining oceanographic drift models and statistical analyses of field data from 1959 to 1993 and investigating effects across trophic levels, we are able to elucidate pathways by which climate influences zooplankton. The results show that both chlorophyll biomass in spring and C. finmarchicus biomass in summer relate positively to a combination of shallow mixed layer depth and increased wind in spring, suggesting that C. finmarchicus biomass in summer is influenced by bottom-up effects of food availability. Furthermore, spatially resolved C. finmarchicus biomass in summer is linked to favorable transport from warmer, core areas to the south. However, increased mean temperature in spring does not lead to increased C. finmarchicus biomass in summer. Rather, spring biomass is generally higher, but population growth from spring to summer is lower, after a warm compared with a cold spring. Our study illustrates how improved understanding of climate effects can be obtained when different datasets and different methods are combined in a unified approach.

Calanus finmarchicus is a marine zooplankton of interest for the aquaculture industry, as well as for nutraceuticals and the cosmetic industry. The chemical composition of C. finmarchicus rapidly changes postmortem due to autolytic processes; in particular phospholipids rapidly degrade to give free fatty acids. The aim of this study was to inactivate autolytic enzymes in C. finmarchicus by applying heat (72°C, 5-30min) through mixing with boiling, fresh water, and further to explore the effects of heat (70°C, 15min) combined with long time storage (-20°C, 12months) of treated and untreated material. Heat treatment (5min) inactivated all tested enzymes and maintained the initial amount of phospholipids, total lipids and crude protein. Storage of untreated material led to complete degradation of all phospholipids, whereas heat treatment resulted in a stable product containing the initial amount of phospholipids and astaxanthin., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

We build on previous research describing correlative links between changes in the abundance of the copepod Calanus finmarchicus , a foundational zooplankton species of the pelagic food web, and diminishing recruitment of young-of-year American lobster (Homarus americanus) to benthic nurseries in the Gulf of Maine. Using parallel 31-year time series of lobster larvae and zooplankton collected on the New Hampshire coast between 1988 and 2018, we investigated how changes in phenology of stage I larval lobster and their putative copepod prey, C. finmarchicus , affect their temporal overlap and potential to interact during the larval season. We found that over the time series both the lobster egg hatch and first appearance of larvae began earlier in the season, a trend significantly correlated with ocean warming. The last appearance of larvae in late summer has been delayed, however, thereby extending the larval season. Even with the longer larval lobster season, the C. finmarchicus season has increasingly been ending before the peak abundance of stage I lobster larvae. The net effect is a widening mismatch in phenology of the two species, an outcome consistent with the hypothesis that changes in abundance and phenology of C. finmarchicus have contributed to recent declines in lobster recruitment. [ABSTRACT FROM AUTHOR]

Annual rhythms are observed in living organisms with numerous ecological implications. In the zooplanktonic copepod Calanus finmarchicus, such rhythms are crucial regarding its phenology, body lipid accumulation, and global carbon storage. Climate change drives annual biological rhythms out of phase with the prevailing environmental conditions with yet unknown but potentially catastrophic consequences. However, the molecular dynamics underlying phenology are still poorly described. In a rhythmic analysis of C. finmarchicus annual gene expression, results reveal that more than 90% of the transcriptome shows significant annual rhythms, with abrupt and dramatic upheaval between the active and diapause life cycle states. This work explores the implication of the circadian clock in the annual timing, which may control epigenetic mechanisms to profoundly modulate gene expression in response to calendar time. Results also suggest an increased light sensitivity during diapause that would ensure the photoperiodic entrainment of the endogenous annual clock. [ABSTRACT FROM AUTHOR]

Recent research highlighted significant marine biological activity during the Arctic winter, with poorly known implications for the biological carbon pump. We used moored instruments to (1) track the development of the pelagic food web of a high‐Arctic marine ecosystem from winter to spring, and (2) assess the role of zooplankton‐mediated processes in the sinking export of particulate organic carbon (POC). Zooplankton collected by a sediment trap at 40 m depth in Kongsfjorden showed a shift in species composition in February coinciding with an inflow of Atlantic water and the return of sunlight. The Atlantic copepod Calanus finmarchicus and the Arctic Calanus glacialis became dominant in the post‐inflow assemblage of large mesozooplankton. However, large copepods were never abundant (0.3–4.6 ind m−3) in January–April in the upper 40 m. Despite the low chlorophyll fluorescence, POC export increased substantially, from 2–13 mg C m−2 d−1 in January–February to 13–35 mg C m−2 d−1 in March–April 2014. By late March, zooplankton fecal pellets contributed largely (23–100%) to this significant POC export before the phytoplankton bloom. The lack of change in copepod and euphausiid population sizes suggests that enhanced feeding activity in the surface layer supported the increasing fecal pellet export. Our results revealed the swift response of active zooplankton in winter, evidenced by increased carbon export, to improved food availability. [ABSTRACT FROM AUTHOR]

Folate, also known as vitamin B9, plays a crucial role in the one-carbon (1C) metabolism, a conserved pathway from microbes to humans. The 1C metabolism, consisting of the folate and methionine cycles, is essential in many biological processes such as nucleotide and protein biosynthesis, cell proliferation, and embryonic development. Despite its functional role, little is known about the 1C metabolism in crustaceans. As part of an ongoing effort to characterize important pathways in Calanus finmarchicus, the biomass-dominant zooplankton in much of the North Atlantic Ocean, we identified transcripts encoding the 1C metabolism enzymes. Using an in silico workflow consisting of a transcriptome mining, reciprocal blasts, and structural analyses of the deduced proteins, we identified the entire set of enzymes in both cycles. The majority encoded for full-length proteins and clustered with homologs from other species. Stage-specific expression was reported, with several transcripts showing high expression in the naupliar stage (e.g., 10-FTHFD, SHMT2) while some methyltransferases (e.g., BHMT, SHMT, DNMT) were more expressed in adults. Overall, this study provides a set of genes which can be used as potential biomarkers of development and reproduction and can be tested in other zooplankters to assess ocean health status monitoring. [ABSTRACT FROM AUTHOR]

Plankton community structure changes seasonally in response to the annual cycles of stratification, temperature, and primary productivity. These communities also change from year-to-year, in some cases exhibiting persistent regime shifts. How changes in physical conditions structure the plankton community and why conditions persist is a fundamental question in oceanography. Continuous plankton recorders have been used to sample the plankton community across the Gulf of Maine since 1961. Historically, this community has had a classic subarctic structure dominated by Calanus finmarchicus. However, during the 1990s, C. finmarchicus became less prominent, and a more diverse community of smaller copepods emerged. This shift was related to an influx of cold, low-salinity water. We show that a similar community shift occurred around 2012. We use high-resolution hydrographic data to link the shift to an influx of saltier water and warmer conditions. By comparing the 1990s with the recent decade, we develop a synthesis for how physical changes lead to community shifts. Our synthesis suggests that the link between the 1990s and 2010s is enhanced water column stratification. We further propose that ecological interactions link declines in C. finmarchicus with the emergence of the more diverse community, drawing parallels with classic food web ecology. [ABSTRACT FROM AUTHOR]

Zooplankton in the Barents Sea has been monitored by the Institute of Marine Research in Norway on autumn cruises since 1986, using a standardized procedure with determination of dry weight biomass in three size fractions following splitting of the sample in two halves. Along with summer data for the early 1980s, we can now describe changes of zooplankton biomass over four decades. The biomass of the central Barents Sea has fluctuated inversely with collapses and recoveries of the Barents Sea capelin stock, which is a major planktivore. Zooplankton biomass in the central Barents Sea was low in 1983 and 1984, driven by low abundance of Calanus finmarchicus , followed by a pronounced peak in 1987 associated with a "first" collapse of the capelin stock. Biomass showed another pronounced peak in 1994, driven by the small size fraction and interpreted to reflect an advective signal from the adjacent Norwegian Sea. In the two most recent decades, there have been divergent trends, with a relatively high biomass in the inflowing Atlantic water, reflecting a second summer generation of C. finmarchicus , and decreased biomass in the central area, reflecting a lower abundance of Calanus glacialis driven by a combined effect of capelin predation and climate. [ABSTRACT FROM AUTHOR]

Fast-sinking zooplankton carcasses and fecal pellets appear to contribute significantly to the vertical transport of particulate organic carbon (POC), partly because of low temperature that decreases microbial degradation during the descent into the deep ocean. Increasing hydrostatic pressure could further reduce the degradation efficiency of sinking POC, but this effect remains unexplored. Here, the degradation of carcasses and fecal pellets of the abundant marine copepod Calanus finmarchicus was experimentally studied as a function of pressure (0.1–100 MPa). Samples were either exposed to elevated pressure in short 1-day incubations or a gradual pressure increase, simulating continuous particle sinking during a 20-day incubation. Both experiments revealed gradual inhibition of microbial respiration in the pressure range of 20–100 MPa, corresponding to 2–10-km depth. This suggests that hydrostatic pressure impedes carbon mineralization of fast-sinking carcasses and fecal pellets and enhances the deep-sea deposition rate of zooplankton-derived organic material. [ABSTRACT FROM AUTHOR]

The demand for mineral resources is increasing mining activities worldwide. In Norway, marine tailing disposal (MTD) is practiced, introducing mineral particles into fjord ecosystems. We investigated the effects of two concentrations (high and low) of fine tailings from a CaCO3 processing plant on early life stages of the marine copepod Calanus finmarchicus. Results show that the exposure did not significantly impact hatching success or development in non- and early feeding life stages. However, feeding stage nauplii ingested tailings, which caused a significantly slower development in later nauplii stages in high exposure groups, with most individuals being two stages behind the control group. Further, high mortality occurred in late nauplii and early copepodite stages in low exposure groups, which could be caused by insufficient energy accumulation and depleted energy reserves during development. Individuals exposed to high exposure concentrations seemed to survive by arresting development and potentially by reduced activity, thereby conserving energy reserves. In nature, slower development could affect lipid storage buildup and reproduction. [ABSTRACT FROM AUTHOR]

Calanus finmarchicus is a keystone zooplankton species that is commercially harvested and is critical in sustaining many important fisheries in the North Atlantic. However, due to their patchy population distributions, they are notoriously difficult to map using traditional ship-based techniques. This study involves the use of a combined approach of standardized ocean colour imagery and radiative transfer modelling to identify reflectance anomalies potentially caused by surface swarms of C. finmarchicus in the northern Norwegian Sea. Here, we have standardized satellite eRGB imagery that depicts a distinct 'red' patch, which coincides with in situ measurements of high surface concentrations of C. finmarchicus. Anomaly mapping using a novel colour matching technique shows a high degree of anomaly within this patch compared to the surrounding waters, indicating the presence of something other than the standard bio-optical model constituents influencing the optics of the water column. Optical closure between modelled and satellite-derived reflectance signals is achieved (and the anomaly is significantly reduced) through the addition of C. finmarchicus absorption into the model. Estimations of the surface concentrations of C. finmarchicus suggest between 80,000 and 150,000 individuals m−3 within the extent of the identified red patch. Furthermore, analysis of the impact of C. finmarchicus absorption on the OC3M algorithm performance points to the potential for the algorithm to over-estimate chlorophyll concentrations if C. finmarchicus populations are present in the surface waters. [ABSTRACT FROM AUTHOR]

Iron is an essential element for the functioning of cellular processes. Ferritins, the major intracellular iron storage proteins, convert the free Fe2+ into the nontoxic Fe3+ which can be stored and transported where needed. To date, little is known about the iron metabolism in copepods; however, in these crustaceans, ferritins have been used as biomarkers of stress and diapause. A limiting factor of these studies has been the use of a single ferritin transcript as a biomarker. In this paper, we in silico mined the publicly available copepod transcriptomes to characterize the multiplicity of the ferritin transcripts in different orders and families. We also examined the expression of ferritin in three ecologically important copepods—Calanus finmarchicus, C. helgolandicus and Temora stylifera—during development and under stress conditions. A full-length transcript encoding ferritin heavy chain has been identified in all 27 mined transcriptomes, with 50% of the species possessing multiple transcripts. Ferritin expression increased in C. finmarchicus during the early–late development transition, and in T. stylifera females exposed to oxylipins at sea. Overall, our results suggest that copepod ferritins can be involved in iron storage, larval development and stress response, thus representing potential biomarker genes for ocean health status monitoring. [ABSTRACT FROM AUTHOR]

Copepods of the genus Calanus are a critical source of food for the North Atlantic right whale (NARW), Eubalaena glacialis. We quantified variations in depth-integrated abundance and vertical distribution of Calanus spp. in the southern Gulf of St. Lawrence (sGSL) in August 2019. While Calanus finmarchicus was the most abundant species of Calanus , the larger C. hyperboreus was prominent in the Shediac Valley, a NARW high-use area, contributing a median of 55% estimated depth-integrated biomass of Calanus spp. during the first leg of the field mission. Near-bottom aggregations of Calanus spp. with concentrations exceeding 1000 ind m−3 occurred primarily at depths ranging from 70 to 90 m. Ontogenetic and diel vertical migrations likely contributed to development of these subsurface aggregations. During the day, Calanus spp. and euphausiids occurred in a compact near-bottom layer, indicating enhanced foraging conditions for NARW. We observed considerable variation in abundance and vertical distribution of Calanus spp. highlighting the dynamic nature of NARW prey distribution at scales of weeks and tens of kilometers in the sGSL. [ABSTRACT FROM AUTHOR]

Knowledge of environmental preferences of the key planktonic species, such as Calanus copepods in the Arctic, is crucial to understand ecosystem function and its future under climate change. Here, we assessed the environmental conditions influencing the development stages of Atlantic Calanus finmarchicus and Arctic Calanus glacialis, and we quantified the extent to which their niches overlap by incorporating multiple environmental data. We based our analysis on a 3‐year seasonal collection of zooplankton by sediment traps, located on moorings in two contrasting Svalbard fjords: the Arctic Rijpfjorden and the Atlantic‐influenced Kongsfjorden. Despite large differences in water temperature between the fjords, local realized ecological niches of the sibling Calanus species overlapped almost perfectly. The exception was the earliest copepodites of C. glacialis in Rijpfjorden, which probably utilized the local ice algal bloom in spring. However, during periods with no sea ice, like in Kongsfjorden, the siblings of both Calanus species showed high synchronization in the population structure. Interestingly, differences in temperature preferences of C. finmarchicus and C. glacialis were much higher between the studied fjords than between the species. Our analysis confirmed the high plasticity of Calanus copepods and their abilities to adapt to highly variable environmental settings, not only on an interannual basis but also in a climate warming context, indicating some resilience in the Calanus community. [ABSTRACT FROM AUTHOR]

Marine ecosystem dynamics can vary on timescales ranging from months to centuries, but many observational data are limited to just a few decades. The bivalve Arctica islandica may live up to five centuries depositing annual growth increments in its shells which can serve as an indicator for ecosystem productivity. In the present study, 154 specimens of A. islandica were collected on the Faroe Shelf and standardised annual growth increments for 143 of them – 44 from coastal stations and 99 from shelf stations – were compared with climatic, oceanographic and biological variables. A. islandica growth from coastal and shelf stations was not correlated with basin-scale climate indices (the AMO index, the NAO index, the AO index or the subpolar gyre index) or, more locally, with windspeed or sea surface temperature on the Faroe Shelf. For the shelf stations there was a significant negative correlation between A. islandica growth and the volume transport of the Faroe Current flowing just north of Faroe Islands (r = -0.62). There was a weak nonsignificant positive correlation with an index of primary production on the Faroe Shelf (r = 0.31) and a strong negative correlation with a zooplankton biomass index in mid-summer (r = -0.76). There was also a strong positive correlation between A. islandica growth and the biomass of the bottom-feeding fish species Melanogrammus aeglefinus two years later (r = 0.62). These results seem to suggest that A. islandica growth may represent the amount of fresh phytoplankton that reaches the near-bottom water layers and could probably be regarded as a proxy for the strength of pelagic-benthic coupling that is modulated through phytoplankton-zooplankton interactions in the overlying water. Our results highlight the potential for A. islandica to serve as a long-term proxy for linking variability in pelagic ecosystem dynamics to demersal fish stocks.

Calanus finmarchicus is a keystone zooplankton species that is commercially harvested and is critical in sustaining many important fisheries in the North Atlantic. However, due to their patchy population distributions, they are notoriously difficult to map using traditional ship-based techniques. This study involves the use of a combined approach of standardized ocean colour imagery and radiative transfer modelling to identify reflectance anomalies potentially caused by surface swarms of C. finmarchicus in the northern Norwegian Sea. Here, we have standardized satellite eRGB imagery that depicts a distinct ‘red’ patch, which coincides with in situ measurements of high surface concentrations of C. finmarchicus. Anomaly mapping using a novel colour matching technique shows a high degree of anomaly within this patch compared to the surrounding waters, indicating the presence of something other than the standard bio-optical model constituents influencing the optics of the water column. Optical closure between modelled and satellite-derived reflectance signals is achieved (and the anomaly is significantly reduced) through the addition of C. finmarchicus absorption into the model. Estimations of the surface concentrations of C. finmarchicus suggest between 80,000 and 150,000 individuals m−3 within the extent of the identified red patch. Furthermore, analysis of the impact of C. finmarchicus absorption on the OC3M algorithm performance points to the potential for the algorithm to over-estimate chlorophyll concentrations if C. finmarchicus populations are present in the surface waters.

The aquaculture sector is in pursuit of sustainable and cost-effective raw materials for feed, and the copepod Calanus finmarchicus is a marine zooplankton species of commercial interest because of its high abundance in northern areas. These copepods have the potential to meet the demand for vast quantities of marine raw materials. However, the lack of an energy- and catch-efficient trawl technology has limited the development of this fishery. Therefore, this study investigated the effect of two central trawl net design parameters mesh size and taper angle to identify which values that provide optimal trade-off balance between gear drag and catch efficiency. We conducted flume tank experiments using a series of plankton nets varying in mesh size (250–1000 μm), solidity ratio (0.54–0.76), and taper angle (5°– 30°) to acquire data on gear drag. The same nets were then used in fishing trials to obtain data on their catch performance. This study shows that zooplankton nets with a mesh size of approximately 500 μm and a low taper angle of about 5° provided the best trade-off between drag and catch performance. • Effect of mesh size and taper angle on performance of zooplankton trawls. • Gear drag and catch efficiency are important performance measures for trawls. • Trade-off between catch efficiency and gear drag when selecting gear mesh size. • Trade-off between catch efficiency and gear drag to when selecting gear taper angle. [ABSTRACT FROM AUTHOR]

The changing Arctic environment is affecting zooplankton that support its abundant wildlife. We examined how these changes are influencing a key zooplankton species, Calanus finmarchicus, principally found in the North Atlantic but expatriated to the Arctic. Close to the ice-edge in the Fram Strait, we identified areas that, since the 1980s, are increasingly favourable to C. finmarchicus. Field-sampling revealed part of the population there to be capable of amassing enough reserves to overwinter. Early developmental stages were also present in early summer, suggesting successful local recruitment. This extension to suitable C. finmarchicus habitat is most likely facilitated by the long-term retreat of the ice-edge, allowing phytoplankton to bloom earlier and for longer and through higher temperatures increasing copepod developmental rates. The increased capacity for this species to complete its life-cycle and prosper in the Fram Strait can change community structure, with large consequences to regional food-webs. [ABSTRACT FROM AUTHOR]

The copepod Calanus finmarchicus (Crustacea, Copepoda) is a key zooplanktonic species with a crucial position in the North Atlantic food web and significant contributor to ocean carbon flux. Like many other high latitude animals, it has evolved a programmed arrested development called diapause to cope with long periods of limited food supply, while growth and reproduction are timed to take advantage of seasonal peaks in primary production. However, anthropogenic warming is inducing changes in the expected timing of phytoplankton blooms, suggesting phenological mismatches with negative consequences for the N. Atlantic ecosystem. While diapause mechanisms are mainly studied in terrestrial arthropods, specifically on laboratory model species, such as the fruit fly Drosophila, the molecular investigations of annual rhythms in wild marine species remain fragmentary. Here we performed a rigorous year‐long monthly sampling campaign of C. finmarchicus in a Scottish Loch (UK; 56.45°N, 5.18°W) to generate an annual transcriptome. The mRNA of 36 samples (monthly triplicate of 25 individuals) have been deeply sequenced with an average depth of 137 ± 4 million reads (mean ± SE) per sample, aligned to the reference transcriptome, and filtered. We detail the quality assessment of the datasets and provide a high‐quality resource for the investigation of wild annual transcriptomic rhythms (35,357 components) in a key diapausing zooplanktonic species. [ABSTRACT FROM AUTHOR]

Ocean physical conditions in the Maritimes Region in 2020 were characterized by generally warm surface and bottom temperatures. The year 2020 was the third warmest of the 51-year time series with 2012 having been the warmest on record. Surface and deep nutrients inventories remained mainly near or below normal on the Scotian Shelf (SS) following the trend of the last 6-7 years. Higher-than-normal deep nitrate concentrations associated with warm salty water were observed in the fall on the eastern side of the Cabot Strait section and at the offshore stations of the Halifax section. The spring phytoplankton bloom on the central and the western SS was later than normal and shorter in duration with either near- or lower-than-normal magnitude. On the eastern SS, bloom conditions developed near the shelf break with normal onset timing and duration. Observations at the Halifax-2 (HL2) station indicated a continued pattern of mainly lower abundance of diatoms and higher abundance of ciliates and flagellates. Zooplankton indices (i.e., Calanus finmarchicus, Pseudocalanus spp., total copepods and noncopepods abundance, and mesozooplankton biomass) were mainly near or lower than average across most of the region but slightly above normal on the Browns Bank section. The abundance of copepod indicator species (i.e., Arctic Calanus, warm-offshore species and warmshelf species) was generally near or slightly lower than normal, although spatial variability was observed. Observations at HL2 also indicate a continued pattern of generally higher-thannormal abundance of small cyclopoid copepods (e.g., Oithona atlantica). Surface temperatures in Bedford Basin were, on average, slightly above normal in 2020, consistent with general trends observed across the SS. From January to September, bottom temperatures continued the trend of primarily negative anomalies observed in 2019. In October, both bottom temperature and salinity reverted to above-normal conditions, suggesting the occurrence of an offshore shelf-water intrusion event. Bottom nitrate, silicate, particulate organic carbon and nitrogen all reverted to below-normal conditions in October, coinciding with the timing of the suspected shelf-water intrusion event. Bottom chlorophyll and phytoplankton conditions were all below normal in 2020, marking a continuation of the primarily negative anomalies observed in these parameters since 2010. The 2019 Continuous Plankton Recorder data indicated lower-than-normal annual abundances of diatoms and dinoflagellates on the Eastern Scotian Shelf (ESS) and Western Scotian Shelf (WSS), while the values of the phytoplankton colour index, a proxy for the phytoplankton biomass, were near (WSS) or above (ESS) normal. The annual abundances of Calanus CI-IV and C. finmarchicus CV-VI were above or near normal on the ESS and below normal on the WSS. Abundances of the other taxa (two arctic Calanus species, three small copepod taxa, two macrozooplankton taxa, and three acid-sensitive taxa) were near or lower than normal on the ESS and WSS, except for hyperiid amphipods, which were more abundant than normal on the ESS. [ABSTRACT FROM AUTHOR]

Size fractionation with 2000 and 1000 μm screens is used by the Institute of Marine Research in Norway in routine monitoring of zooplankton biomass. This study examines the separation of taxa by this procedure. For copepods and cladocerans, the fractionation separates individuals according to their size in a consistent and predictable manner. Individuals up to 0.4 mm in width are contained in the small fraction (<1 mm). From width 0.4 to 0.8 mm, there is a progressive shift from the small to the medium fraction (1–2 mm). From about 0.8 mm width, individuals start to be contained in the large fraction (>2 mm). For Calanus finmarchicus , young copepodites CI–CIII are contained in the small fraction, while the older stages CV and adults are contained in the medium fraction. Small copepods (Oithona , Oncaea , Microcalanus , Pseudocalanus) are contained in the small fraction, as are most appendicularians and meroplanktonic invertebrate larvae. The large fraction includes large copepods, larger individuals of chaetognaths, krill and amphipods. The consistency of separation of taxa by size will help to interpret and improve the ecological relevance of results on size-fractioned zooplankton biomass in the Barents Sea as well as other high-latitude areas. [ABSTRACT FROM AUTHOR]

• Two different sources of the Calanus population were observed in a Subarctic fjord/shelf system: a local and an advected part. • A prolonged phytoplankton bloom lasting 10 weeks can support both local and advected copepods. • These copepods provide the essential nauplii prey for one of the world's largest fish stocks, Northeast Arctic cod, over an extended time period. • The fjord food web was tightly coupled between the phytoplankton spring bloom, the local part of the Calanus population (trophic level 1.8–2.4) and cod larvae (high levels of wax esters). • On the shelf, the impact of advected Calanus on the food web was at its starting point (low trophic level, large difference of δ13C of POM and Calanus). Fjord and shelf food webs are frequently supplemented by the advection of external biomass, which in high-latitude seas often comes in the form of lipid-rich copepods that can support a wide range of fish species, including Northeast Arctic cod (Gadus morhua). A seasonal match or mismatch at the lower trophic levels (phytoplankton and zooplankton) is central in determining how much energy and biomass is available for higher trophic levels (fish). Here, we quantify the inflow of the copepod Calanus finmarchicus into the Vestfjorden fjord system using high-resolution measurements of ocean currents and zooplankton (laser optical plankton counter). We evaluate a spatio-temporal match/mismatch between the phytoplankton bloom and Calanus and assess the input of advected copeods at the lower trophic level fjord and shelf food web based on an integrative approach employing stable isotope analyses (C, N), fatty acid trophic marker analyses, and biovolume spectrum analyses. Our results suggest two different sources of the Calanus population in the fjord/shelf system: one fraction overwintered locally and started ascending early to feed on the phytoplankton bloom that peaked around April 11. The other fraction had only recently (end of April) been and still was being advected from the oceanic overwintering habitats. Ca. 119 g C/s of Calanus were advected into the fjord, comparable to the biomass of Calanus advected into an Arctic fjord, and the mesozooplankton community was dominated by the copepod. The fjord food web was tightly coupled between the phytoplankton spring bloom, the local part of the Calanus population (trophic level 1.8–2.4) and cod larvae (high levels of wax esters). On the shelf, our results suggest that the impact of advected Calanus in the food web is at its starting point (low trophic level, large difference of δ13C of POM and Calanus). We highlight important factors that can contribute to the successful spawning of Northeast Arctic cod: an extended phytoplankton bloom that can support both locally and advected Calanus , which in turn can supply the essential nauplii prey for first-feeding cod larvae. [ABSTRACT FROM AUTHOR]

The ubiquitous oceanic copepod Calanus finmarchicus is the major link between primary producers and important fish stocks in the North Atlantic Ocean and adjacent seas. Despite over a century of research on growth and development of this key species, the effect of predation risk on these processes remains elusive. We tested how food level and chemical cues from a fish predator influence growth and development of C. finmarchicus, using a predator naïve laboratory population. Copepods reached adult stage earlier both in response to high food and to predator cues in our experiment. High food also increased growth and lipid accumulation. In contrast, perceived predation risk triggered reduced size and lipid fullness, indicating a decoupling of growth and development rates. Our results demonstrate that chemical predator cues can influence life history strategies in C. finmarchicus, and suggest that present and future patterns in oceanic zooplankton size and population dynamics may also reflect differences in predation risk. [ABSTRACT FROM AUTHOR]

The impacts of grazing by meso- and microzooplankton on phytoplankton primary production (PP) was investigated in the surface layer of the western North Atlantic during spring. Shipboard experiments were performed on a latitudinal transect at three stations that differed in mixed layer depth, temperature, and mesozooplankton taxonomic composition. The mesozooplankton community was numerically dominated by Calanus finmarchicus at the northern and central station, with Calanus hyperboreus also present at the northern station. The southern station was >10 ffiC warmer than the other stations and had the most diverse mesozooplankton assemblage, dominated by small copepods including Paracalanus spp. Microzooplankton grazing was detected only at the northern station, where it removed 97% of PP. Estimated clearance rates by C. hyperboreus and C. finmarchicus suggested that at in-situ abundance these mesozooplankton were not likely to have a major impact on phytoplankton abundance, unless locally aggregated. Although mesozooplankton grazing impact on total phytoplankton was minimal, these grazers completely removed the numerically scarce > 10 mm particles, altering the particle-size spectrum. At the southern station, grazing by the whole mesozooplankton assemblage resulted in a removal of 14% of PP, and its effect on net phytoplankton growth rate was similar irrespective of ambient light. In contrast, reduction in light availability had an approximately 3-fold greater impact on net phytoplankton growth rate than mesozooplankton grazing pressure. The low mesozooplankton grazing impact across stations suggests limited mesozooplanktonmediated vertical export of phytoplankton production. The constraints provided here on trophic transfer, as well as quantitative estimates of the relative contribution of light and grazer controls of PP and of grazer-induced shifts in particle size spectra, illuminate food web dynamics and aid in parameterizing modeling-frameworks assessing global elemental fluxes and carbon export. [ABSTRACT FROM AUTHOR]

Our knowledge of the marine plankton in high Arctic regions under winter conditions is very limited, especially during the polar night. Recent winters in the Barents Sea and adjacent waters have been anomalously warm, strongly influencing zooplankton communities. The structure of the mesozooplankton in relation to environmental conditions was investigated in Svalbard waters during November–December 2015. A total of 39 taxa were identified in the samples. Diversity of the mesozooplankton, as assessed by the Shannon index and by evenness, was lower when compared with published summer estimates. Cluster analysis revealed three groups of stations that differed primarily in the abundance/biomass of major species rather than by the presence or absence of specific taxa. Copepods constituted more than 98% of the total mesozooplankton abundance with Calanus finmarchicus, Calanus glacialis, Microcalanus spp., Oithona similis, and Pseudocalanus spp. being the most frequent. Total mesozooplankton biomass varied over a wide range (0.4–59.6 g dry mass m–2) with a high average value (± standard error) of 12.2 ± 4.2 g DM m–2. The maximum biomass was found in Isfjorden; this is the greatest mesozooplankton stock estimation for the Arctic during winter conditions. High mesozooplankton biomasses were also recorded in waters south of Svalbard. Redundancy and linear regression analyses revealed that mesozooplankton variability was strongly connected with the depth of sampling layer, mean salinity, bottom temperature, and latitude, suggesting that the observed distribution pattern of mesozooplankton abundance and species composition were related to local topography, circulation, and frontal zones. Another possible factor that might influence the mesozooplankton assemblage is the recent warming in the Arctic. [ABSTRACT FROM AUTHOR]

The northern Svalbard shelf region is part of the Atlantic advective contiguous domain along which nutrients, phyto- and mesozooplankton are advected with Atlantic Water from the Norwegian Sea along the Norwegian shelf break and into the Arctic Ocean. By applying the SINMOD model, we investigated how much mesozooplankton may be advected into the northern Svalbard shelf region. We also compared this supply with the local mesozooplankton production. To achieve this, we selected a box north of Svalbard and calculated the in- and outflux of Atlantic Calanus finmarchicus and Arctic Calanus glacialis. The average biomass inside the box ranged between 0.5 and 3.0 g C month–2 in March and August, respectively. Annually, 18.8 g C month–2 of advected (and locally produced) mesozooplankton would be available for predators inside the box before it is advected out. The advection of mesozooplankton reached 12 times more than the average biomass within the box. The model projects significance variability in mesozooplankton advection which may be explained by the hitherto non-quantified recirculation in the northern Fram Strait and differences in the geographic origin of the mesozooplankton source population. The results imply that grazing upon mesozooplankton in the Atlantic advective contiguous domain north of Svalbard is greatly advantageous for pelagic predators. It could represent an important food source for fish, birds, and whales. It is suggested that mesozooplankton encountered on the shelf north of Svalbard may derive from populations along the North Norwegian shelf break, in some years as far south as the Lofoten/Vesterålen region. This illustrates the extent and significance of the Atlantic advective contiguous domain for the European shelf of the Arctic Ocean which apparently depends on significant food supply through expatriates. Primary production on the shelf is lower than C consumption and thus the European shelf of the AO is presumably net-heterotrophic.

Our research focused on the analysis of interannual variability of zooplankton in the Kola Section (the Barents Sea) in the period of current warming in the Arctic basing on previously unpublished data. The zooplankton community was investigated based on the analysis of 240 plankton samples, collected in late May–early June 2009–2017. A total of 74 zooplankton taxa of nine phyla were identified in the plankton samples, but copepods were the most diverse and numerous taxonomic group. The biodiversity index varied considerably from year to year, but a stable tendency for the index to increase since the beginning of the period studied was observed. Copepods dominated in terms of abundance and biomass, comprising on average 73–96% of the total zooplankton abundance and 81–96% of the total zooplankton biomass. Calanus finmarchicus was the main zooplankton species utterly dominated by abundance and biomass (on average 92 and 97% respectively). Considerable differences in zooplankton abundance and biomass at different stations of the section were observed. Although the investigations were carried out during a warming period, interannual differences in zooplankton abundance and biomass were observed. Zooplankton biomasses were higher in the years with higher temperatures and stronger water inflow. [ABSTRACT FROM AUTHOR]

Linking production, transfer and subsequent bioavailability of nutritionally significant matter from phytoplankton to higher trophic levels is a fundamental aspect in understanding marine food webs. The plant–animal interface is of interest because of the highly variable transfer between producers and consumers, and the myriad of factors that influence it. Essential fatty acids (EFAs) are dietary nutrients that are necessary for normal function in all consumers, yet it remains unclear how efficiently they are transferred through marine food webs. We introduced a 13C-labelled carbon source to the cryptophyte Rhodomonas salina to quantify primary production of two omega-3 long-chain polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). We investigated transfer and assimilation efficiencies of these EFAs from phytoplankton to the calanoid copepod Calanus finmarchicus in an 8-day feeding experiment. We found low production of both EFAs in R. salina. Assimilation efficiencies of both EFAs ranged from 5 to 15% throughout the experiment, remaining slightly higher on average for DHA. This was mirrored in more efficient trophic transfer of DHA (up to 28%, compared to 13% for EPA). These results add to previously scarce experiments empirically quantifying the assimilation and transfer efficiency of EFAs in a basic marine planktonic food chain. [ABSTRACT FROM AUTHOR]

Studies of zooplankton spatial distribution and feeding were conducted in the eastern part of the Barents Sea in early October 2014. The study period was characterized by positive anomalies of the water temperature in the upper mixed layer and by the dominance of coccolithophorids in phytoplankton. The scale of spatial variability of zooplankton biomass (6.1–43.3 mg DW m–3) over the 30 000-km2 investigated area was comparable to the range of interannual variation of zooplankton biomass in the Barents Sea. Calanus finmarchicus and Metridia longa dominated in the zooplankton community. The spatial distribution of C. finmarchicus was correlated with the depth: at the stations, where the depth exceeded 250 m, the biomass was threefold higher than that at the shallower stations. Both species performed diel vertical migrations ascending to the upper 50-m layer during night and actively consuming there coccolithophorids and tintinnids Acanthostomella norvegica. Taking into account the contribution of tintinnids, the amount of assimilated organic carbon in C. finmarchicus CV, CIV and M. longa CV, CIV was 2.6, 8.3 and 3.5, 4.9% of body carbon content, respectively, and compensated therefore the metabolic costs. Grazing impact on the autotrophic phytoplankton by the populations of C. finmarchicus and M. longa did not exceed 5% of its biomass and was preconditioned by the abundance and the feeding activity of migrating copepods. [ABSTRACT FROM AUTHOR]

The North Atlantic right whale (NARW), Eubalaena glacialis , feeds on zooplankton, particularly copepods of the genus Calanus. We quantified interannual variation in anomalies of abundance and biomass of Calanus spp. and near-surface and near-bottom ocean temperature and salinity from 19 subregions spanning the Gulf of Maine–Georges Bank (GoM–GBK), Scotian Shelf (SS), Gulf of St. Lawrence (GSL) and Newfoundland and Labrador Shelves. We analyzed time series from 1977 to 2016 in GoM–GBK, 1982 to 2016 in southwest GSL and 1999 to 2016 in remaining areas. Calanus finmarchicus dominated abundance and biomass, except in the GSL where Calanus hyperboreus was abundant. The biomass of Calanus spp. declined in many subregions over years 1999–2016 and was negatively correlated with sea surface temperature in GoM–GBK and on the SS. We detected ''regime shifts" to lower biomass of Calanus spp. in the GoM–GBK in 2010 and on the SS in 2011. In the GoM–GBK, shifts to lower biomass of C. finmarchicus coincided with shifts to warmer ocean temperature and with published reports of changes in spatial distribution and reduced calving rate of NARW. We hypothesize that warming has negatively impacted population levels of Calanus spp. near their southern range limit, reducing the availability of prey to NARW. [ABSTRACT FROM AUTHOR]

Abstract The spatial distribution of mesozooplankton was investigated in relation to environmental conditions along the Kola Transect (69°30′–79°00′N, 33°30′E) during autumn (September 2011) and early winter (mid-November 2012). Mesozooplankton abundance averaged 964 and 740 individuals m−3 and biomass averaged 55 and 32 mg dry mass m−3 in 2011 and 2012, respectively. Cluster analysis showed good accordance of the mesozooplankton assemblages with the three main types of water masses present in the region. The first assemblage, dominated by Calanus finmarchicus and Oithona similis , but including neritic taxa, was associated with Murmansk Coastal Water. The second assemblage, with Calanus spp. contributing the majority of the total mesozooplankton biomass, was connected with Atlantic waters. The third assemblage, dominated by Calanus glacialis, was associated with cold Arctic waters. Redundancy analysis revealed that the explanatory factors significantly influencing the community structure of mesozooplankton were surface and bottom temperature, and depth of the sampling layer. Almost 64% of the total mesozooplankton fluctuations could be explained by changes in these environmental variables. Inter-seasonal changes in the structure of mesozooplankton were associated with higher abundances of Calanus hyperboreus , Copepoda nauplii, Microsetella norvegica , Aglantha digitale , Oikopleura vanhoeffenni , and Mertensia ovum and lower numbers of Oithona atlantica and young stages of Paraeuchaeta spp. in September 2011. Regional and seasonal comparisons of the total mesozooplankton biomass observed in the present study with sample data from the summer of 2003–2012 suggest that the mean values were higher in autumn season of 2011 due to differences in sampling layers. Highlights • Mesozooplankton assemblages were related to three main types of water masses. • Seasonal differences were connected to Copepoda abundance. • Mesozooplankton biomass was higher than the mean summer values. • Water temperature and sampling layer influenced mesozooplankton distribution. [ABSTRACT FROM AUTHOR]

Recent observations confirm the rising temperatures of Atlantic waters transported into the Arctic Ocean via the West Spitsbergen Current ( WSC). We studied the overall abundance and population structure of the North Atlantic keystone zooplankton copepod Calanus finmarchicus, which is the main prey for pelagic fish and some seabirds, in relation to selected environmental variables in this area between 2001 and 2011, when warming in the Arctic and Subarctic was particularly pronounced. Sampling within a 3-week time window each summer demonstrated that trends in the overall abundance of C. finmarchicus varied between years, with the highest values in 'extreme' years, due to high numbers of nauplii and early copepodite stages in colder years (2001, 2004, 2010), and contrary to that, the fifth copepodite stage (C5) peaking in warm years (2006, 2007, 2009). The most influential environmental variable driving C. finmarchicus life cycle was temperature, which promoted an increased C5 abundance when the temperature was above 6°C, indicating earlier spawning and/or accelerated development, and possibly leading to their development to adults later in the summer and spawning for the second time, given adequate food supply. Based on the presented high interannual and spatial variability, we hypothesize that under a warmer climate, C. finmarchicus may annually produce two generations in the southern part of the WSC, what in turn could lead to food web reorganization of important top predators, such as little auks, and induce northward migrations of fish, especially the Norwegian herring. [ABSTRACT FROM AUTHOR]

Zooplankton availability during spring and summer determines the growth and survival of first-feeding fish larvae, and thus impacts the recruitment to both fish prey species and commercial fish stocks. On the Faroe shelf, however, the relative importance of oceanic versus neritic zooplankton species has hitherto not been well understood. In this study, spatio-temporal variability in zooplankton community structure and size spectra on the Faroe shelf is investigated using observations from late April during the period 1997–2016. The main objective was to explore which environmental variables influence the zooplankton community structure in early spring. The zooplankton community in the permanently well mixed central shelf inside the tidal front consists of a mixture of neritic, cosmopolitan and oceanic species. In this region, redundancy analyses showed that chlorophyll concentration had a positive effect on abundance of neritic copepods and meroplankton as well as all zooplankton < 1.2 mm. The abundance variability of these species shows increased production around 2000 and 2008–2009. The highest zooplankton abundance, mainly consisting of Calanus finmarchicus , is however observed off-shore from the tidal front, especially on the western side of the Faroe Plateau. A shift in C. finmarchicus phenology occurred around 2007, resulting in earlier reproduction of this species, and this variability could not be explained by the employed regional environmental parameters. Our results indicate that the Faroe shelf biological production is more dependent on the local primary production and neritic zooplankton species than on the large oceanic C. finmarchicus stock. [ABSTRACT FROM AUTHOR]

Microplastics (<5 mm) are ubiquitous in the marine environment and are ingested by zooplankton with possible negative effects on survival, feeding, and fecundity. The majority of laboratory studies has used new and pristine microplastics to test their impacts, while aging processes such as weathering and biofouling alter the characteristics of plastic particles in the marine environment. We investigated zooplankton ingestion of polystyrene beads (15 and 30 μm) and fragments (≤30 μm), and tested the hypothesis that microplastics previously exposed to marine conditions (aged) are ingested at higher rates than pristine microplastics. Polystyrene beads were aged by soaking in natural local seawater for three weeks. Three zooplankton taxa ingested microplastics, excluding the copepod Pseudocalanus spp., but the proportions of individuals ingesting plastic and the number of particles ingested were taxon and life stage specific and dependent on plastic size. All stages of Calanus finmarchicus ingested polystyrene fragments. Aged microbeads were preferred over pristine ones by females of Acartia longiremis as well as juvenile copepodites CV and adults of Calanus finmarchicus . The preference for aged microplastics may be attributed to the formation of a biofilm. Such a coating, made up of natural microbes, may contain similar prey as the copepods feed on in the water column and secrete chemical exudates that aid chemodetection and thus increase the attractiveness of the particles as food items. Much of the ingested plastic was, however, egested within a short time period (2–4 h) and the survival of adult Calanus females was not affected in an 11-day exposure. Negative effects of microplastics ingestion were thus limited. Our findings emphasize, however, that aging plays an important role in the transformation of microplastics at sea and ingestion by grazers, and should thus be considered in future microplastics ingestion studies and estimates of microplastics transfer into the marine food web. [ABSTRACT FROM AUTHOR]

In the advective realm of the seas, it is challenging to disentangle the role of regional and local processes on zooplankton populations. However, comparative studies of spatially separated zooplankton populations can provide valuable insights into this issue. We studied interannual abundance variation of the key zooplankton species Calanus finmarchicus and C. hyperboreus in three near-shore locations of the Nordic Seas: off northern Norway, Svalbard, and northern Iceland. Average abundances of both species were similar among locations, while in each location the abundance of C. finmarchicus was about an order of magnitude higher than the abundance of C. hyperboreus. The abundance of both species decreased in northern Norway, while C. finmarchicus abundance increased in northern Iceland. C. finmarchicus abundance in northern Norway covaried with regional climate, while the Svalbard Calanus populations were related to local environment (hydrography, phytoplankton). In northern Iceland, C. finmarchicus abundance covaried with local environmental factors, while C. hyperboreus abundance covaried with climate variability. Top-down forcing could not be investigated. The results indicate that the mechanisms relating regional climate variability (North Atlantic and Arctic oscillations) to Calanus abundance are mediated through advection of water masses, while more local environmental variability involved bottom-up processes or advection. [ABSTRACT FROM AUTHOR]

Calanus finmarchicus is the dominant copepod species in the Norwegian Sea, where it plays a key role in the ecosystem by transferring energy from primary producers to higher trophic levels. This paper analyses a 17-year time series, 1996–2012, on C. finmarchicus collected within the Atlantic Water mass along the Svinøy transect in the southeastern Norwegian Sea. We use the spring abundance of adult as a proxy for the size of C. finmarchicus ’ overwintered population. The inter-annual trend in spring abundance of adult C. finmarchicus in the 200–0 m depth-stratum is assessed while accounting for spring population development to the adult stage represented by day of year for sampling, inter-annual changes in timing of population development, and spatial differences. For the most oceanic stations, a significant inter-annual trend in spring abundance of adult C. finmarchicus was revealed using generalized additive models (GAM). This trend primarily consists in an increase prior to year 2000 and a decrease between years 2000 and ca. 2011. For the stations closer to the coast, the identified inter-annual trend is a decrease during a longer period from the late 90s until ca. 2011. From 2000 to 2011, our estimates suggest a 50% decrease for the most oceanic stations, and as much as an 81% decrease for the stations closer to the coast. In addition the results suggest a consistent change in phenology over the years and the stations. The predicted spring peak of overwintered adult population abundance is suggested to become shorter by 3 days, and the predicted maximum of abundance to take place 4 days earlier over the 17 years of the time-series. The results highlight significant changes in intensity and timing of the overwintered population of a key zooplankton species in the Norwegian Sea that may have important implications on the scale of an entire ecosystem. [ABSTRACT FROM AUTHOR]

The copepod Calanus finmarchicus is an important part of the diet for several large fish stocks feeding in the Atlantic waters of the Barents Sea. Determining the origin of the new generation copepodites present on the Barents Sea shelf in spring can shed light on the importance of local versus imported production of C. finmarchicus biomass in this region. In this study, we couple large-scale spatiotemporal survey data (> 30 years in both Norwegian Sea and Barents Sea areas) with drift trajectories from a hydrodynamic model to back-calculate and map the spatial distribution of C. finmarchicus from copepod to egg, allowing us to identify potential adult spawning areas. Assuming the adult stage emerges from overwintering in the Norwegian Sea, our results suggest that copepodites sampled at the Barents Sea entrance are a mix of locally spawned individuals and long-distance-travellers advected northwards along the Norwegian shelf edge. However, copepodites sampled farther east in the Barents Sea (33°30′E) are most likely spawned on the Barents Sea shelf, potentially from females that have overwintered locally. Our results support that C. finmarchicus dynamics in the Barents Sea are not, at least in the short-term, solely driven by advection from the Norwegian Sea, but that local production may be more important than commonly believed. [ABSTRACT FROM AUTHOR]

In the marine environment, chaetognaths are among the major predators of zooplankton. The most common Chaetognatha species in the Arctic coastal waters are Parasagitta elegans and Eukrohnia hamata. Their distribution and size structure and potential predatory impact on the zooplankton community were analyzed in Isfjorden (Svalbard Archipelago). Parasagitta elegans dominated in terms of biomass (1.5 mg DM ∙ m−3) over E. hamata (0.09 mg DM ∙ m−3), and the clear pattern of chaetognaths' size distribution was noticed: smaller individuals occurred in the upper water layers, while larger ones were observed near the fjords' bottom. Based on Redundancy Analysis (RDA) followed by variation partitioning, the zooplankton community was influenced by environmental variables (36.6%) and by chaetognaths (16.6%), while the joint impact for both groups of these predictors was 46.6%. Both increasing temperature and P. elegans influenced medium-sized and small copepods (e.g., Calanus finmarchicus, Oithona similis), pteropods, and meroplankton larvae (upper layers), while E. hamata was related to larger copepods (e.g., Calanus hyperboreus , Metridia longa) at greater depths. The study showed different predation pressure of P. elegans and E. hamata in the Arctic fjord and revealed complex interactions within the zooplankton community and marine environment. • Environment and chaetognaths had influenced the zooplankton structure. • Cheatognaths' predation influence on selected zooplankton species was confirmed. • Depending on size class, chaetognaths influenced both large and small copepods. • The zooplankton biomass in the water column decreased with depth. • Atlantification may affect the occurrence and biomass of Calanus glacialis. [ABSTRACT FROM AUTHOR]

The distributions of phytoplankton, zooplankton and hydrographic features off the coast of northern Norway were assessed in late April – early May 2019 using ship-based observations (CTD casts and Moving Vessel Profilers) and autonomous vehicles. A satellite chlorophyll climatology was generated to place our in-situ observations within a longer temporal sequence. Substantial spatial and temporal variability on all scales was observed in both the observations and climatology. Spring phytoplankton accumulation usually is initiated in the south on the continental shelf, and advanced in a northerly direction through time. Accumulations in the surface layer of deeper waters off the continental shelf occurred 2–3 weeks later than those on the shelf. During our survey, primary productivity was greatest in offshore waters where nutrients were not depleted and exceeded 2 g C m−2 d−1. The greatest Calanus finmarchicus abundances were associated with low chlorophyll concentrations, suggesting a major impact of grazing on phytoplankton biomass, but estimates of phytoplankton growth and zooplankton removal suggested that Calanus was responsible for a variable fraction (3–69%) of the daily chlorophyll changes. Vertical changes in chlorophyll were related to physical features during some transects, but to grazing and sinking in others. Understanding the spatial and temporal variations of the coupling of phytoplankton to zooplankton is essential to effective management of this important commercial species in Norwegian waters. • Phytoplankton primary productivity was assessed in northern Norway continental shelf and slope. • Biomass and productivity were greatest over the continental slope. • A satellite climatology showed that blooms spread from continental shelf to deep water. • Phytoplankton vertical distributions were controlled by multiple processes. • Copepods and chlorophyll were largely inversely correlated. [ABSTRACT FROM AUTHOR]

• Selective copepod grazing and water mass origin impacted spring bloom composition. • Diatom bloom enhanced zooplankton recruitment and deep carbon export. • Spring bloom composition impacted summer plankton community. • Mixo- and heterotrophic protists dominated the nutrient-poor summer months. • Copepod grazers controlled the summer protist community. Seasonal plankton time-series data are presented from Kongsfjorden from two years with contrasting environmental conditions. Kongsfjorden (west coast of Spitsbergen – 79°N) integrates inputs from Atlantic and Arctic waters, and glacier run-off, and is thus a prime location to study impacts on ecosystem dynamics of key environmental drivers that are relevant across the Arctic. Despite extensive research in Kongsfjorden, seasonally-resolved data are scarce. From late April/early May to early September 2019 and 2020, we conducted pelagic sampling at a mid-fjord station at mostly weekly to bi-weekly resolution investigating the environmental drivers of phyto- and zooplankton community composition and phenology. During spring 2019, Atlantic water masses with temperatures > 1 °C were found throughout the upper 250 m of the water column, and little sea ice occurred in the fjord. Spring 2020, in turn, was characterized by the presence of local water masses with sub-zero temperatures and relatively extensive sea-ice cover. The most striking contrast between the two years was the difference in phytoplankton spring bloom composition. In 2019, the spring bloom was dominated by the colonial stage of the haptophyte Phaeocystis pouchetii and diatoms played a minor role , while the spring bloom in 2020 was dominated by diatoms of the genus Thalassiosira succeeded by P. pouchetii. Selective grazing by large copepods and water mass structure seem to have been the decisive factors explaining the marked difference in diatom spring bloom biomass between the years while similar spring abundances of P. pouchetii in both years indicated that this species was less impacted by those factors. Our data suggest that differences in spring bloom composition impacted trophic transfer and carbon export. Recruitment of the dominant copepods Calanus finmarchicus and C. glacialis , Cirripedia and euphausiid larvae as well as the export of carbon to the seabed was more efficient during the diatom-dominated compared to the P. pouchetii– dominated spring bloom. In summer, the plankton composition shifted towards a flagellate-dominated community characterized by mixo- and heterotrophic taxa adapted to a lower nutrient regime and strong top-down control by copepod grazers. However, residual silicic acid after the P. pouchetii– dominated spring bloom fueled a late summer diatom bloom in 2019. Our data provide a first glimpse into the environmental drivers of plankton phenology and underline that high-resolution monitoring over many annual cycles is required to resolve the ephemeral variations of plankton populations against the backdrop of climate change. [ABSTRACT FROM AUTHOR]

The growth of Calanus finmarchicus nauplii was studied through three spawning seasons (2007, 2009 and 2011) using flow-through tubes. Natural seston was collected every second day and added as food source using a peristaltic pump. A mixture of cultured microalgae supplied in surplus concentration was used as a control treatment. No significant correlation between growth and food concentration measured as Chlorophyll a (Chla) or particulate organic carbon (POC) was detected, but the growth rate was significantly related to the content of EPA (20:5n-3) and DHA (22:6n-3) in the seston. The growth rate was overall higher for nauplii fed cultured microalgae compared to the nauplii fed natural seston. Although the nauplii fed algae cultures were fed surplus food, the growth did vary between the growth periods. Furthermore, the growth rate for nauplii fed natural seston and for nauplii fed cultured algae were positively related, suggesting that the maternal condition and the food quality experienced by the mothers could explain some of the variation in naupliar growth rate. We present lipid class data on Calanus finmarchicus eggs from field samples that, contrary to previous studies, showed a high content of wax esters. Fatty acid analyzes of eggs, nauplii stages and copepodites from field samples showed that eggs and nauplii have a similar fatty acid composition and that the main increase in the content and share of DHA and EPA was from nauplii to copepodite. The secondary production measured as naupliar growth was compared to the secondary production measured as carbon specific female egg production rate. The secondary production measured as egg production was generally higher than the secondary production measured as naupliar growth early in the spring, whereas the opposite situation was observed during post-bloom situations in late spring/early summer.