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The presence of zooplankton in marine ecosystems is an important factor affecting toxin production in dinoflagellates. However, whether the production of paralytic shellfish toxins (PSTs) by Gymnodinium catenatum and Alexandrium pacificum is affected by substances produced by zooplankton is not yet fully understood. This study assessed the effects of zooplankton extracts on cell abundance, pigment concentration and composition, chlorophyll-a-specific primary production (Chl-a SP), and PST production in G. catenatum and A. pacificum, isolated from Korean coastal waters. In addition, a novel group of hydroxybenzoate PSTs known as GC toxins, which lack commercial reference standards, was evaluated. No significant differences were observed in cell abundance, pigment composition, or Chl-a SP in the experimental group of G. catenatum strains exposed to zooplankton extracts compared to the control group. However, the production of PSTs, including GC toxins, was significantly enhanced when the strain was exposed to extracts of Calanus finmarchicus. Meanwhile, in the A. pacificum strain, some experimental groups showed significant differences in cell abundance and pigment composition, while Chl-a SP significantly decreased in all experimental groups. In addition, PST production was stimulated by the addition of C. finmarchicus extracts. No GC toxins were detected in the A. pacificum strain. This study demonstrated that substances derived from C. finmarchicus enhance the production of PSTs in G. catenatum and A. pacificum. Our findings will improve the current understanding of the occurrence and development mechanisms of PSTs in marine ecosystems and contribute to developing strategies to efficiently secure standard reference toxin products using toxic dinoflagellates. [ABSTRACT FROM AUTHOR]

The ongoing global climate crisis increases temperatures in polar regions faster and with greater magnitude than elsewhere. The decline of Arctic sea ice opens up new passages, eventually leading to higher anthropogenic activities such as shipping, fishing, and mining. Climate change and anthropogenic activities will increase contaminant transport from temperate to Arctic regions. The shipping industry uses copper as an antifouling coating. Copper is an essential element but becomes toxic at excess concentrations, and its use may inadvertently affect non-target organisms such as copepods. Copper affects copepods by lowering reproductive output, prolonging developmental time, and causing increased mortality. As data on copper sensitivity of polar copepods at low temperatures are rare, we conducted onboard survival experiments with the Arctic region's most common copepod species (Calanus finmarchicus, C. glacialis, C. hyperboreus). Acute survival tests were done for up to 8 days on individuals in 70 ml bottles at 1 °C with nominal copper concentrations ranging from 3 to 480 μg L−1. We used a reduced General Unified Threshold model for Survival (GUTS) to analyse the data, and placed our results in the context of the few published copper sensitivity data of the Antarctic and temperate copepod species at low temperatures. The sensitivity of Cu exposure was similar between the three Calanus species. However, a model comparison suggests that the tested C. glacialis population is less sensitive than the other two species in our experiments. Compared to published data, the three Arctic species appear slightly less sensitive to copper compared to their Antarctic counterparts but more compared to their temperate ones. Our literature search revealed only a few available studies on the copper sensitivity of polar copepods. In the future, this species group will be exposed to more pollutants, which warrants more studies to predict potential risks, especially given possible interactions with environmental factors. [ABSTRACT FROM AUTHOR]

Many methods have been proposed to model the spatial distribution of a species. While some methods have been specifically designed for this purpose, others are well‐known statistical tools that can be used in many scientific fields. In this paper, I propose a new ecological niche model, called the Environmental String Model (ESM), that is based on the concept of environmental string, which is defined as being a combination of environmental variables, with as many nodes as environmental variables. There are two types of environmental strings: (1) the abundance‐known string and (2) the abundance‐unknown string (or target string) for which an estimation of abundance is searched. The novelty of the model is that it assesses the abundance associated with a target string from nearby abundance‐known strings, which preserve the local multidimensional relationships with the target string. The model does not provide an abundance estimate in the absence of data from a similar environment and it can therefore deal with truncated spatial distributions or niches. It is tested in the North Atlantic Ocean on two key copepod species, Calanus finmarchicus and Calanus helgolandicus, which have been monitored by the Continuous Plankton Recorder (CPR) survey for decades. I investigate the influence of variables on model performance. I show that the model reconstructs the mean spatial distribution and seasonal fluctuations in both Calanus well. When compared with generalized linear models (GLMs), generalized additive models (GAMs) and generalized regression neural network (GRNN), the ESM gives the best performance. I propose a number of indicators to evaluate the robustness of estimated abundance in space and time and show how the model may be extended to presence/absence or presence‐only data. I think that the ESM could be used to fill gaps in any sampling program such as the CPR survey and many satellite databases (e.g., ocean color and photosynthetically active radiation). [ABSTRACT FROM AUTHOR]

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

This corrigendum addresses errors in a scientific article about copepod communities in the Barents Sea. The errors are related to figures, tables, and supplementary materials in the original article. The corrected versions of these elements are provided. The study found that the secondary production of copepods varied between 2018 and 2019, with different copepod groups dominating in different regions. Calanus spp. were the main contributors to copepod secondary production in the Arctic Ocean basin. The corrigendum emphasizes that the errors do not alter the scientific conclusions of the article. [Extracted from the article]

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]

Globally, impacts of climate change display an increasingly negative development of marine biomass, but there is large regional variability. In this analysis of future climate change on stock productivity proxies for the North Sea, the Norwegian Sea, and the Barents Sea, we have provided calculations of accumulated directional effects as a function of climate exposure and sensitivity attributes. Based on modelled changes in physical and biogeochemical variables from three scenarios and knowledge of 13 different stocks' habitats and response to climate variations, climate exposures have been weighted, and corresponding directions these have on the stocks have been decided. SSP1‐2.6 gives mostly a weak cooling in all regions with almost negligible impacts on all stocks. SSP2‐4.5 and SSP5‐8.5 both provide warmer conditions in the long term but are significantly different in the last 30 years of the century when the SSP5‐8.5 warming is much stronger. The results show that it is the current stocks of cod and Calanus finmarchicusin the North Sea, and polar cod and capelin in the Barents Sea that will be most negatively affected by strong warming. Stocks that can migrate north into the northern seas such as hake in the Norwegian Sea, or stocks that are near the middle of the preferred temperature range such as mackerel and herring in the Norwegian Sea and cod and Calanus finmarchicus in the Barents Sea, are the winners in a warmer climate. The highly different impacts between the three scenarios show that multiple scenario studies of this kind matter. [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]

Respiration of lipids by copepods during diapause (overwintering dormancy) contributes to ocean carbon sequestration via the seasonal lipid pump (SLP). Parameterizing this flux in predictive models requires a mechanistic understanding of how life history adaptation in copepods shapes their timing of exit from diapause. We investigate the optimal phenology of Calanus finmarchicus in the Norwegian Sea using an individual-based model in which diapause exit is represented as a trait characterized by phenotypic mean and variance. Without interannual variability, optimal exit correlated with the onset of the spring phytoplankton bloom and phenotypic variance was of no benefit. In contrast, copepods endured reduced fitness and adopted bet-hedging strategies when exposed to interannual variability in bloom timing and predation: later exit from diapause and phenotypic variance maintained adult numbers in anomalous late-bloom years. Exit nevertheless remained well before the peak of the bloom which is a favorable strategy when low predation early in the year enhances survival of eggs and early developmental stages. Our work highlights the complex interactions between C. finmarchicus and its environment and the need for improved understanding of bet-hedging strategies and the cues of diapause exit to progress the representation of the SLP in global biogeochemical models. [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]

The article "Life in turbulent waters: unsteady biota–flow interactions across scales" explores how aquatic organisms interact with turbulent water bodies, focusing on the physical forces and conditions they experience. It discusses the impact of turbulence on organisms at different spatial and time scales, highlighting behavioral and ecophysiological responses. The research emphasizes the need for diverse taxa in laboratory studies to understand relationships between hydrodynamics and organism behavior accurately. Additionally, the article touches on the control exerted by large-scale turbulent features on the distribution of matter and organisms, showcasing the complex interplay between turbulence and aquatic ecosystems. [Extracted from the article]

In November–December 2023, an expedition of the Murmansk Marine Biological Institute of the Russian Academy of Sciences, on board the R/V Dalnie Zelentsy conducted hydrological, hydrochemical, hydrobiological, and radioecological research in the area west of the Spitsbergen archipelago and on the century-old Kola Meridian transect in the Barents Sea. New data on thermohaline conditions, plankton, and radionuclides during the polar night were obtained at 54 oceanographic and hydrobiological stations. Positive water temperature anomalies show continuation of the warm climate cycle in the Barents Sea. The revealed activation of florogenesis in the western Barents Sea is probably caused by advection of Atlantic waters. Based on an analysis of the population structure of Calanus finmarchicus and C. glacialis in the waters of Spitsbergen, a specific feature of seasonal size variability of species in summer and winter was determined. [ABSTRACT FROM AUTHOR]

The timing of spring phytoplankton blooms is crucial to many species that have adapted their development to benefit from the enhanced feeding opportunity they offer. Any change to their timing may affect the productivity of an entire ecosystem. This study explores the relationship between the ocean climate, the timing of the spring bloom and the secondary production on the Newfoundland and Labrador shelf. It is found that over interannual cycles, the ocean climate is significantly correlated with the timing of the bloom and the abundance of Calanus finmarchicus, a key zooplankton species for the ecosystem. It also appears that the spring bloom is initiated by the onset of ocean re‐stratification following winter mixing. Understanding how annual variation in climate relates to the timing of the spring bloom and zooplankton abundance, that is, the base of the marine food web, can inform the development of ecosystem‐informed models for higher trophic levels. [ABSTRACT FROM AUTHOR]

Calanus finmarchicus is an abundant calanoid copepod in the New York Bight (NYB) that has energy-dense lipid stores. This study measured C. finmarchicus abundance, lipid storage and energy density and compared it to two other abundant calanoid species in the region. We compared the NYB C. finmarchicus preyfield characteristics with data from two other NW Atlantic coastal ecosystems, the Gulf of Maine (GoM) and Cape Cod Bay (CCB). Copepods from net tows were identified, enumerated, photographed and measured. These data were used to calculate animal biovolume and lipid content as well as the volumetric energy density of the copepod preyfield. C. finmarchicus were most abundant in spring and summer and the mean lipid storage of C. finmarchicus remained largely constant regardless of season and location within the NYB. Centropages typicus were abundant enough in the winter to be more energy-rich than C. finmarchicus. Temora longicornis, while also abundant, never surpassed the energy density of C. finmarchicus. C. finmarchicus in the NYB were comparably lipid-rich to those from the GoM and CCB. C. finmarchicus in the NYB can be a reliable energy source for local predators due to their high spring and summer abundances and year-round storage of high-energy wax esters. [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]

Shrimp feed formulations have moved towards less fish meal and more of the readily available and cheaper plant proteins. To counteract the lower attractiveness and palatability of plant proteins, feeds are supplemented with ingredients known to have chemoattractive properties that will increase feed intake. This study investigated the putative chemoattractive effect of Calanus finmarchicus hydrolysate, when used as a dietary supplement in shrimp feeds. C. finmarchicus is a zooplankton species native to the northern Atlantic Ocean and is a novel and sustainable raw material for shrimp feed products. Diet attractiveness was evaluated in a 24-day feeding trial with whiteleg shrimp (Litopenaeus vannamei) by measuring the intake of 12 diets with various levels of fish meal, calanus hydrolysate, and krill (Euphausia superba) meal. Higher inclusion rates of both ingredients resulted in increased feed intake, and supplementing the high fish meal diet with calanus hydrolysate gave a statistically significant higher feed intake. Low molecular weight peptides, chemoattractive amino acids, and the water-soluble nature of the hydrolysate could explain the chemoattractive properties observed in the study. [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]

Copepod size and energy content are influenced by regional and seasonal variation in temperature and food conditions, with implications for planktivorous consumers such as the endangered North Atlantic right whale (Eubalaena glacialis). Historical data (1990–2020) on Calanus finmarchicus stage CV copepodite prosome length and oil sac metrics were analyzed to determine the extent of variation in individual body size and estimated lipid and energy content in five regions of the Northwest Atlantic continental shelves [Gulf of Maine (GoM), Scotian Shelf (SS), Gulf of St. Lawrence (GSL), St. Lawrence Estuary (SLE) and Newfoundland Shelf]. Large-scale spatial patterns in size and lipid content were related to latitude, indicating that C. finmarchicus CV in the GSL and SLE were historically larger in body size, and had significantly higher lipid content compared with those in the GoM and the SS. The observed patterns of C. finmarchicus CV size and lipid storage capacity suggest that regional variation in whale prey energy content can play a role in the suitability of current and future whale foraging habitats in the Northwest Atlantic, with the larger lipid-rich individuals in the GSL providing a high-quality diet compared with those in southern areas. [ABSTRACT FROM AUTHOR]

Interspecific hybridization events are on the rise in natural systems due to climate change disrupting species barriers. Across taxa, microsatellites have long been the molecular markers of choice to identify admixed individuals. However, with the advent of high‐throughput sequencing easing the generation of genome‐wide datasets, incorrect reports of hybridization resulting from microsatellite technical artefacts have been uncovered in a growing number of taxa. In the marine zooplankton genus Calanus (Copepoda), whose species are used as climate change indicators, microsatellite markers have suggested hybridization between C. finmarchicus and C. glacialis, while other nuclear markers (InDels) never detected any admixed individuals, leaving the scientific community divided. Here, for the first time, we investigated the potential for hybridization among C. finmarchicus, C. glacialis, C. helgolandicus and C. hyperboreus using two large and independent SNP datasets. These were derived firstly from a protocol of target‐capture applied to 179 individuals collected from 17 sites across the North Atlantic and Arctic Oceans, including sympatric areas, and second from published RNA sequences. All SNP‐based analyses were congruent in showing that Calanus species are distinct and do not appear to hybridize. We then thoroughly re‐assessed the microsatellites showing hybrids, with the support of published transcriptomes, and identified technical issues plaguing eight out of 10 microsatellites, including size homoplasy, paralogy, potential for null alleles and even two primer pairs targeting the same locus. Our study illustrates how deceptive microsatellites can be when applied to the investigation of hybridization. [ABSTRACT FROM AUTHOR]

Maintenance of the health of our oceans is critical for the survival of the oceanic food chain upon which humanity is dependent. Zooplanktonic copepods are among the most numerous multicellular organisms on earth. As the base of the primary consumer food web, they constitute a major biomass in oceans, being an important food source for fish and functioning in the carbon cycle. The potential impact of climate change on copepod populations is an area of intense study. Omics technologies offer the potential to detect early metabolic alterations induced by the stresses of climate change. One such omics approach is lipidomics, which can accurately quantify changes in lipid pools serving structural, signal transduction, and energy roles. We utilized high-resolution mass spectrometry (≤2 ppm mass error) to characterize the lipidome of three different species of copepods in an effort to identify lipid-based biomarkers of copepod health and viability which are more sensitive than observational tools. With the establishment of such a lipid database, we will have an analytical platform useful for prospectively monitoring the lipidome of copepods in a planned long-term five-year ecological study of climate change on this oceanic sentinel species. The copepods examined in this pilot study included a North Atlantic species (Calanus finmarchicus) and two species from the Gulf of Mexico, one a filter feeder (Acartia tonsa) and one a hunter (Labidocerca aestiva). Our findings clearly indicate that the lipidomes of copepod species can vary greatly, supporting the need to obtain a broad snapshot of each unique lipidome in a long-term multigeneration prospective study of climate change. This is critical, since there may well be species-specific responses to the stressors of climate change and co-stressors such as pollution. While lipid nomenclature and biochemistry are extremely complex, it is not essential for all readers interested in climate change to understand all of the various lipid classes presented in this study. The clear message from this research is that we can monitor key copepod lipid families with high accuracy, and therefore potentially monitor lipid families that respond to environmental perturbations evoked by climate change. [ABSTRACT FROM AUTHOR]

Spatial population synchrony, defined as spatial covariation in population density fluctuations, exists across different temporal and spatial scales. Determining the degree of spatial synchrony is useful for inferring environmental drivers of population variability in the wake of climate change. In this study, we applied novel statistical methods to detect spatial synchrony patterns of Calanus finmarchicus on the Northeast U.S. Shelf at multiple spatiotemporal scales using unevenly distributed data. Our results reveal that C. finmarchicus subpopulations connected by advection are not necessarily in synchrony, indicating that the degree of synchrony is likely influenced by heterogeneity of local habitats. In addition, regionally synchronous environmental conditions (e.g., sea surface temperature) may not play as significant a role in influencing subregional population dynamics as was previously hypothesized. Overlooking the spatial heterogeneity of synchronous patterns at different time scales could lead to erroneous inferences of potential environmental drivers responsible for C. finmarchicus variability. [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]

The world will be dependent on the development of novel feed ingredients from renewable sources to ensure sustainable growth of the aquaculture industry. Zooplankton like Calanus finmarchicus are viable new raw material candidates, as they have optimal nutrient profiles for aquatic animals and may be sustainably harvested in large volumes. In this study, the aim was to investigate if a protein hydrolysate of C. finmarchicus was able to influence the growth performance of fish. The effect of dietary inclusion of hydrolysates was tested in a feeding trial with European sea bass (Dicentrarchus labrax) juveniles, benchmarking calanus hydrolysate (CH) against commercially available hydrolysates. The diet with CH inclusion yielded increased growth, with significantly higher body weight than hydrolysates of sardine and tuna fish at the end of the trial. The observed growth-promoting effects were further examined using an in vitro model with skeletal muscle cells from Atlantic salmon. Through bioactivity experiments with muscle cells grown in media containing CH, low-molecular fractions were found to have the greatest positive effect on proliferation, viability, and expression of muscle-specific genes. Characterization of the most potent fraction revealed an abundance of small peptides, along with amino acids and marine metabolites associated with increased muscle growth. [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]

Changes in the physical oceanography of the Northwest Atlantic stemming from both natural and anthropogenic climate change impact the foraging ecology and distribution of endangered North Atlantic right whales. In this study, right whale sightings from 1990 to 2018 were analyzed to examine decadal patterns in monthly habitat use in 12 high‐use areas. Depth‐integrated abundances of late‐stage Calanus finmarchicus and Calanus hyperboreus were also analyzed for decadal variations in the right whale foraging habitats. There were significant differences in the occurrence, seasonal timing, and persistence of foraging habitats across these three decades. In the decades of the 1990s and the 2010s, prey was less abundant than in the 2000s, corresponding to reduced use of the Southeast US calving grounds in the winter, increased use of Cape Cod Bay in winter and spring, and reduced use of Roseway Basin in the fall. In the 2010s, right whale sightings increased in Southern New England and the Gulf of St. Lawrence in the spring and summer, respectively. Summertime declines in the 2010s in late‐stage copepod abundances in the Gulf of Maine and surrounding regions, as well as in the Gulf of St. Lawrence, indicate that recent increased use of the Gulf of St. Lawrence is driven by a decline in prey in traditional foraging habitats rather than by an increase in prey in the new foraging habitat. This analysis of decadal‐scale differences in right whale sightings and prey abundance is critical for redefining right whale distribution patterns for the most recent (post‐2010) decade. [ABSTRACT FROM AUTHOR]

Calanus finmarchicus were reared from eggs to adults at 12°C and 16°C with non‐limiting food in combination with ambient (600 μatm) and high (1100 μatm) pCO2. These conditions are likely to be encountered by the species at the southern margins of its biogeographical range by the end of the century. Dry weight (DW), carbon (C) and nitrogen (N) mass, oil‐sac volume (OSV), fatty acid composition (FA), and oxygen consumption rates (OCR) were measured on newly molted stage CV copepodites and recently molted adult females. By focusing our measurements on these precise events in the life cycle, we were able to obtain a more accurate comparison of growth and respiration across treatments. Copepods raised at 12°C had a significantly greater DW, OSV, and C and N mass than those raised at 16°C High pCO2, independent of temperature, was associated with a further increase in the DW and C content of the copepods. Interactive effects of temperature and pCO2 resulted in a larger OSV at low temperature and high pCO2. Mass‐specific respiration rates were significantly lower at lower temperatures and elevated pCO2 suggesting that the increase in mass (DW, C, and OSV) resulted from reduced metabolic cost. The composition of fatty acids in the copepods varied mainly with temperature. Two fatty acids varied with pCO2: 16:0 tended to decrease with higher pCO2 and 18:3n−3 tended to increase with higher pCO2. These observations suggest that elevated pCO2/lower pH in future oceans may have a beneficial effect on C. finmarchicus. [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]

Calanus finmarchicus is one of the most important zooplankton species in the North Atlantic. The zooplankton is currently being harvested and industrially processed to a marine oil product for human consumption as a marine nutraceutical containing long-chain omega-3 polyunsaturated fatty acids. This oil is very rich in wax esters, a lipid class where fatty acids are esterified to long chain fatty alcohols. In this paper we describe a simple method to 1) isolate the wax esters from the other lipid classes present in the oil, 2) hydrolyze the wax esters, and 3) separate the fatty acids from the fatty alcohol, all by means of solid phase extraction. Starting with an average of 322 mg Calanus oil, we obtained 75 mg fatty alcohols and 63 mg fatty acids. Contrary to previously described techniques, our method neither oxidize the fatty alcohols to fatty acids, nor are the fatty acids methylated, allowing the native, unesterified fatty acids and fatty alcohols to be used for further studies, such as in cell culture experiments to study the metabolic effects of these specific lipid fractions rather than the intact oil or wax esters. [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]

Every year, large numbers of zooplankton migrate from the surface ocean to depths of 500–2000 m to hibernate. Through this migration, they actively transport organic carbon to the deep ocean, where it is used to fuel metabolic needs. This active transport of carbon is thought to be highly efficient, as carbon metabolized by copepods is directly injected deep into the ocean's interior. The significance of this process in view of global carbon cycling remains an open question. Here, we focus on five representative, diapausing copepod species (Calanus finmarchicus, Calanus hyperboreus, Calanoides acutus, Calanoides natalis, and Neocalanus tonsus) distributed in the Arctic, Atlantic, Indian, and Southern Oceans. For each species, we compute both carbon injection (how much carbon is transported below the euphotic zone during zooplankton migration and left there as dissolved inorganic carbon) and carbon sequestration (the amount of carbon stored in the ocean's interior following diapausing zooplankton‐mediated injection). In total, the five species considered here contribute 0.4–0.8% of total biological carbon export, and 0.8–3.3% of total carbon sequestration mediated by the biological pump (assuming a total carbon export of ~ 10 PgC yr−1 and sequestration of ~ 1300 PgC). Including other species in this inventory would increase the contribution of diapausing copepods to the biological carbon pump, but requires more precise estimates of copepods' distribution, abundance, and metabolic requirements. [ABSTRACT FROM AUTHOR]

The reproductive success of marine ectotherms is especially vulnerable in warming oceans due to alterations in adult physiology, as well as embryonic and larval survival prospects. These vital responses may, however, differ considerably across the species' geographical distribution. Here we investigated the life history, focusing on reproductive ecology, of three spatially distant populations (stocks) of Atlantic cod (Gadus morhua, Gadidae) (50–80° N), in the Irish/Celtic Seas‐English Channel Complex, North and Barents Seas, under past and projected climate. First, experimental tracking of spawning behaviour evidenced that the ovulation cycle is highly distressed at ≥9.6 (±0.25)°C (Tup). This knife‐edge threshold resulted in erratic spawning frequencies, whereas vitellogenin sequestration remained unaffected, indicating endocrine rather than aerobic scope constraints. Cod in the Celtic Sea‐English Channel are, therefore, expected to show critical stock depensation over the next decades as spawning grounds warm above Tup, with Irish Sea cod subsequently at risk. Second, in the relatively cooler North Sea, the northward retraction of Calanus finmarchicus (Calanidae) and Para‐Pseudocalanus spp. (Clausocalanidae) (1958–2017) limit cod larvae feeding opportunities, particularly in the southernmost subarea. However, the contrasting increase in Calanus helgolandicus (Calanidae) does not counteract this negative effect, likely because cod larvae hatch ahead of its abundance peaks. Overfishing again comes as a twin effect. Third, in the still relatively cold Barents Sea, the sustainably harvested cod benefit from improved food conditions in the recent ice‐free polar region but at the energetic cost of lengthier and faster spawning migrations. Consequently, under climate change local stocks are stressed by different mechanistic factors of varying management severity. [ABSTRACT FROM AUTHOR]

An overview of chemical and biological oceanographic conditions in the Gulf of St. Lawrence in 2021 is presented as part of the Atlantic Zone Monitoring Program (AZMP). AZMP data as well as data from regional monitoring programs are analyzed and presented in relation to long-term means in the context of a warming trend that began in 2010. These long-term means are typically calculated using 1999-2020 as a reference period. Oxygen levels at 300 m reached a record-low concentration in the northwest and central Gulf and in Cabot Strait. Nitrate inventories in the surface layer (0-50 m) of the Gulf were either near or below normal, with record-low levels in the Estuary and northwest Gulf. Mid-layer nitrate inventories (50-150 m) were also below normal in these two subregions, but near or above normal in the other regions. In the bottom layer (150 m-bottom), positive anomalies were found in all Gulf regions with record-high inventories everywhere but in the Estuary. Positive deep nitrate anomalies have been observed regularly since 2012 in the Cabot Strait and the central Gulf and are associated with intrusions of warm and salty waters, but they have been less common in the Estuary over the last decade. The recent increase in the nitrate inventory of the bottom layer is mostly associated with negative anomalies of the N:P ratio and positive anomalies of the Si:N ratio. Annual inventories of vertically integrated chlorophyll a (chl a; 0-100 m) were near normal in all regions except for the Estuary and northwest Gulf, where they were above normal. In these two subregions, the second highest inventories of chl a were observed during fall. Most regions have regularly shown above-normal chl a inventories during fall since about 2014. In contrast, phytoplankton biomass derived from satellite data mostly showed negative annual and fall anomalies in most of the ocean colour polygons over the last four years, including several record-low values in 2021. Spring bloom metric anomalies indicated that the bloom was generally on time but was slightly less intense than normal. Zooplankton biomass was either near or below normal everywhere in the Gulf, with a record-low level in the Estuary/northwest Gulf region. Calanus finmarchicus annual abundance was near normal except at Rimouski station, where it was slightly above normal. C. hyperboreus abundance showed widespread negative anomalies, including a record-low level in the northeast Gulf. Small calanoids were at record-high abundances at Rimouski station and in the Estuary/northwest Gulf region, and their abundances were also above normal in the Magdalen Shallows, and at the Shediac Valley station. Abundances of warm-water copepods were also at record-high levels in the Estuary/northwest Gulf region as well as in northeast Gulf and Magdalen Shallows, and abundances were also above normal in other regions. Cold-water copepod abundances were either near normal or above normal, and record-high values were observed at both high-frequency monitoring stations. The characterization of C. finmarchicus phenology at Rimouski station indicated that the peak of early copepodite stages (CI-CIII) was the earliest and longest-lasting peak ever recorded. [ABSTRACT FROM AUTHOR]

To provide a baseline description of copepod assemblages in the Pechora Sea, an estuarine area with great economical and ecological importance, we conducted a survey during the summer season. A total of 24 copepod taxa were identified in the study, with Acartia longiremis, Calanus finmarchicus, Centropages hamatus, Copepoda nauplii, Eurytemora affinis, Oithona similis, Pseudocalanus spp., and Temora longicornis being the most numerous. The high diversity (Shannon index = 2.51 ± 0.06), density (18,720 ± 3376 individuals m−3) and biomass (89 ± 18 mg dry mass m−3) of copepods were revealed. Populations of common small copepod taxa were dominated by the young stages, indicating spawning, while older copepodites prevailed among medium- and large-sized species, showing that their reproduction occurred before our survey. Cluster analysis indicated three groups of stations that mainly differed in the abundance of particular species. There were clear associations between copepod assemblages and environmental variables. Statistical analyses showed significant correlations between copepod abundance and water temperature or sampling depth, while other factors had a lesser influence. Our results suggest a strong effect of local circulation and currents on the spatial pattern of the copepod assemblages in the study area. This study may be useful for future biomonitoring in the south-eastern Barents Sea. [ABSTRACT FROM AUTHOR]

Calanus oil, an oil extracted from the marine crustacean Calanus finmarchicus, is one of the richest sources of omega-3 and poly-unsaturated fatty acids. Although calanus oil has been shown to have a significant anti-hypertensive, anti-inflammatory, anti-fibrotic and anti-obesity effects in various cardiovascular diseases, but little is known about its effect on pathological cardiac hypertrophy. Thus, the present study was carried out to evaluate the therapeutic effect of calanus oil on cardiac hypertrophy. Cardiac hypertrophy was induced by subcutaneous injections with isoproterenol (5 mg/kg b.w) for 14 consecutive days. Calanus oil (400 mg/kg) was given orally for 4 weeks. Cardiac pathological remodeling was evaluated by echocardiography, after which morphometric, biochemical, histological and ultrastructural analyses were performed. Calanus oil treatment significantly ameliorated isoproterenol-induced structural and functional alterations in echocardiography. Calanus oil also reduced the relative heart weight, significantly decreased the elevated cardiac enzymes (LDH and CK-MB) and the lipid peroxidation marker (MDA), augmented the myocardial antioxidant status (TAC), and ameliorated the histopathological and ultrastructural changes in cardiac tissues and prevented interstitial collagen deposition. The present study, for the first time, provided morphometric, biochemical, histological and ultrastructural evidences supporting the promising anti-hypertrophic effect of calanus oil against ISO-induced cardiac hypertrophy. This anti-hypertrophic effect of calanus oil is via regulating myocardial remodeling and oxidative stress. Therefore, it could be used as potential pharmacological intervention in the management of cardiac hypertrophy. [ABSTRACT FROM AUTHOR]

In recent decades, recruitment of young-of-year lobsters to benthic nursery habitats in the Gulf of Maine was regionally synchronized and exhibited correlative links with changes in the abundance of the copepod Calanus finmarchicus, a foundational zooplankton species of the pelagic food web. The spatial scale at which recruitment dynamics were correlated indicated that recruitment processes were not as strongly coupled to trends in spawner abundance as might be expected, but, rather, were influenced by common, ecosystem-scale processes. Here we explored how local- and basin-scale zooplankton dynamics and oceanographic indicators in the Gulf of Maine correlated with lobster settlement indices and each other since the late 1980s. Our analysis indicates that lobster settlement trends in southwestern Gulf of Maine study areas, from Midcoast Maine to Cape Cod Bay, tend to be significantly correlated with basin-wide C. finmarchicus dynamics and the composition of waters entering the Gulf of Maine through the Northeast Channel. In contrast, lobster settlement in the northeastern Gulf, from Penobscot Bay to the Bay of Fundy, tended to correlate more strongly to C. finmarchicus variability in the Bay of Fundy region, which was distinct in earlier years but converged with the broader basin-scale processes in the latter years. Our results are consistent with the hypothesis that the combined effect of climate-related declines in abundance and phenological shifts of C. finmarchicus have contributed to declines in lobster settlement over the past decade, and justify further research into the mechanisms of this interaction. These changes also align with the weakening influence of cold Labrador Slope Water and strengthening effects of warm Gulf Stream waters that precipitated an ecosystem-wide regime shift in the Gulf of Maine over the past decade and may have greater implications for lobster recruitment than previously suspected. [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]

Diapausing populations of Calanus finmarchicus at depth in the Lofoten Basin (LB) return to the continental shelf and slope off the Lofoten‐Vesterålen Islands during the phytoplankton spring bloom to feed and spawn, forming surface swarms with a great abundance. To study how overwintering populations of C. finmarchicus move with the deep currents and return to the shelf, Lagrangian transport characteristics of particles in deep water between 2008 and 2019 were analyzed using Global Ocean Reanalysis and Simulation re‐analysis data and Lagrangian Coherent Structures (LCSs). Our analyses revealed that persistent eastward transport of diapausing C. finmarchicus between LB and continental slope occurred mainly between 600 and 1,100 m in the Arctic Intermediate Water. The consistency of the vertical distributions of C. finmarchicus abundance and salinity further suggests that physical factors control the horizontal distribution of the species. Hovmöller diagrams of kinetic energy indicate that there is an eastward advection of mean current at depth. The co‐occurrence between the eastward transport of LCSs and the eastward advection of the mean current provides direct evidence that the life history of C. finmarchicus is subjected to physical control in the Norwegian Sea. Plain Language Summary: Overwintering populations of the copepod Calanus finmarchicus in the Lofoten Basin (LB) are critical for maintaining its life cycle and food web in the northern Norwegian Sea. Horizontal advection and particle tracking simulation between 2008 and 2019 were performed using reanalysis data. Our analyses revealed that eastward transport between 600 and 1,100 m in the Arctic Intermediate Water below the Atlantic Water was responsible for moving C. finmarchicus from the LB to the continental slope. The consistency of the vertical distributions of C. finmarchicus and salinity further suggests that physical factors control the horizontal distribution of the species. The trend of decreasing abundance of C. finmarchicus from west to east in January results from the eastward transport of the species and its accumulation on the continental slope. Eastward transport from the basin to the slope is a key process in the life cycle of C. finmarchicus and demonstrates the importance of large‐scale physical‐biological interactions in Nordic Seas. Key Points: Lagrangian Coherent Structures reveal persistent eastward transport between 600 and 1,100 m depth in winter in the northern Norwegian SeaThere is a strong similarity between the eastward advection of the mean current and the eastward transport of diapausing Calanus finmarchicusThis process is a part of the potential spatial and temporal closure of C. finmarchicus life histories at the basin‐slope‐shelf [ABSTRACT FROM AUTHOR]

A physical model of a Burgers vortex was created in the laboratory with characteristics corresponding to dissipative‐scale eddies that copepods are likely to encounter in turbulent flows. The swimming behavior of three marine copepod species is assessed as a function of vortex strength in and around the flow structure with the vortex axis aligned vertically or horizontally in the water. The studied species are Acartia tonsa, an estuarine copepod with a hop‐sink swimming style; Temora longicornis, a coastal copepod with a cruise swimming style; and Calanus finmarchicus, an open‐ocean copepod with a cruise‐sink swimming style. The results show that copepods change their swimming behavior with the intensity of the Burgers vortex and reveal species‐specific responses in nearly all kinematic parameters. A. tonsa and C. finmarchicus exhibited the strongest behavioral response to increasing vortex strength and T. longicornis exhibited the weakest response. A. tonsa and T. longicornis showed no response to changes in vortex orientation, whereas the behavior of C. finmarchicus revealed some vortex orientation dependence. One common behavior among the species is that the swimming trajectory shape becomes increasingly curved and spiral around the vortex core with increasing vortex strength, which provides a means of local aggregation and increased encounter rate with food and mates. The results are interpreted in relation to differences in swimming style and setal morphology among the species. [ABSTRACT FROM AUTHOR]

The Celtic Sea is a productive fishing ground, therefore identifying the relative importance of fishing and environmental factors on fish stock dynamics is crucial for developing our understanding of sustainable yields and to operationalize Ecosystem Based Fisheries Management (EBFM). We investigated the effect of environmental variables and fishing on the relative abundance inferred from catch-per-unit-effort (CPUE), of twelve demersal stocks (i.e., cod, haddock, whiting, anglerfish, hake, megrim, plaice, sole, lesser-spotted dogfish, spurdog, Trisopterus spp., skates and rays) in the Celtic Sea from 1997 to 2019 (23 years). Annualized time series (1997-2019) of net primary production, bottom temperature, copepod abundance (Calanus finmarchicus and Calanus helgolandicus) and North Atlantic Oscillation index were used to characterize key environmental variables. Fishing exploitation rates (F/FMSY) were used to represent fishing pressure and CPUE trends derived from an International Bottom Trawl Survey (IBTS) were used to infer abundance. We used redundancy analysis to identify key explanatory variables and then dynamic factor analysis to assess their relationships with the CPUE series and identify underlying patterns in the unexplained temporal variation. Our results show that for the majority of demersal fish species, the CPUE trends were strongly influenced by fishing exploitation rates. The gradual reduction in exploitation rates observed throughout the study period most likely led to the partial recovery of cod, spurdog, hake, megrim, plaice, whiting, Trisopterus spp., and the skates and rays. In addition, exploitation patterns on one stock influenced CPUE trends of other demersal stocks (e.g., hake, megrim, plaice, lesser-spotted dogfish, sole). We also observed that the CPUE of whiting, hake and plaice increased when C. finmarchicus were abundant in the plankton. We infer from our findings in the investigated time series that the recovery of cod, spurdog, hake, megrim, plaice, whiting, Trisopterus spp., and the skates and rays in the Celtic Sea remains dependent on controlling fishing mortality, and this would not, at least for now, be confounded by the environmental conditions.

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]

While marine ecosystems in polar areas were thought to be mostly inactive during the polar night, recent observations in the Arctic highlight that dynamic biological interactions occur across all trophic levels. One particularly interesting observation made repeatedly is the occurrence of Calanus finmarchicus , a key species at the base of the food web, in the upper part of the water column in early January. This contrasts with the confirmed life cycle of this copepod, which predicts descent to overwintering depths in autumn and ascent at the end of the winter. Here, we compiled 6 years of data from the polar night to explore this unusual behaviour and to investigate the underlying mechanisms that may cause these surface aggregations. Highest abundance of C. finmarchicus in surface waters was closely related to Polar Surface Water in the vicinity of the sea ice edge. A total of six hypotheses are assessed to explain this distribution pattern, which includes passive transport and active behaviour as a way to improve survival chances or food access. In the context of climate change and sea ice decrease, the presence of lipid-rich copepods in cold surface waters could be a key parameter in driving the spatial distributions of top predators in the Arctic. [ABSTRACT FROM AUTHOR]

The lipid-rich calanoid copepod, Calanus finmarchicus , plays a critical role in the Gulf of Maine pelagic food web. Despite numerous studies over the last several decades, a clear picture of variability patterns and links with key environmental drivers remains elusive. This study applies model-based scaling and sensitivity analyses to a regional plankton dataset collected over the last four decades (1977–2017). The focus is to describe the gulf-wide spatio-temporal patterns across three major basins, and to assess the relative roles of internal population dynamics and external exchanges. For the spring stock, there is strong synchrony of interannual variability among three basins. This variability is largely driven by internal population dynamics rather than external exchanges, and the internal population dynamics are more sensitive to the change of top-down mortality regime than the bottom-up forcings. For the fall stock, the synchrony among basins weakens, and the variability is influenced by both internal mortality and external dilution loss. There appears to be no direct connection between the spring stock with either the preceding or subsequent fall stock, suggesting seasonal or sub-seasonal scales of population variability and associated drivers. The results highlight seasonally varying drivers responsible for population variability, including previously less recognized top-down control. [ABSTRACT FROM AUTHOR]

The copepod Calanus finmarchicus was investigated in four Subpolar Basins, Labrador, Irminger, Iceland, and Norwegian Seas, during spring, covering the time of ascent, grazing, and initiation of reproduction in the area. Lipid content, spawning activity, and stage composition and vital rates, such as egg and faecal pellet production were measured and linked to environmental parameters. Specific egg- and faecal pellet production rates varied with diatom biomass and were negatively correlated with temperature. Comparison of the various biological indicators revealed different life history traits C. finmarchicus has adopted in the different basins. In Labrador Sea, the females have invested in large eggs compared to the remaining basins. Labrador and Irminger Sea C. finmarchicus invest in size that we propose to be adaptation to cope with warmer overwintering habitats resulting in larger potential lipid storage capacity, while the Iceland and Norwegian Sea females can invest their remaining lipid storage in spring to fuel lipid-driven egg production. Grazing pressure on the phytoplankton community was estimated and compared between copepod and two dominating groups of protozooplankton; ciliates and heterotrophic dinoflagellates. Despite approximately the same biomass in the upper 100 m, the grazing impact of the protozoan grazers was an order of magnitude higher than the C. finmarchicus dominated mesozooplankton. This illustrates the importance to also include the smallest grazers when studying the spring bloom in high latitude marine ecosystems if the fate of the primary production should be fully understood. [ABSTRACT FROM AUTHOR]

The vertical migrations performed by zooplankton at daily and seasonal scales are important for marine ecosystem dynamics and biogeochemical cycles. We analysed associations between seasonal variation in abundance and depth distribution of the copepod Calanus finmarchicus and temperature and predation pressure from visual (capelin and herring) and non-visual (ctenophores) predators, using data from a > 30-year survey in the southwestern Barents Sea. Calanus finmarchicus abundances were significantly reduced in upper waters with increased capelin biomass, possibly due to a combination of predation mortality and active avoidance of the upper layer. The weighted mean depth of Calanus finmarchicus tended to become shallower, and abundances in deeper layers lower, with a high probability of ctenophore occurrence, possibly due to a predation effect at depth. Temperature influenced the seasonal timing of Calanus finmarchicus , but appeared less important for depth distribution. This study illustrates how climate-driven changes in the physical and biological environment can influence the seasonal and vertical distribution of zooplankton, which has major implications for the flow of energy and nutrients in marine ecosystems. [ABSTRACT FROM AUTHOR]

The traditional view is that the Arctic polar night is a quiescent period for marine life, but recent reports of high levels of feeding and reproduction in both pelagic and benthic taxa have challenged this. We examined the zooplankton community present in Svalbard fjords, coastal waters, and the shelf break north of Svalbard, during the polar night. We focused on the population structure of abundant copepods (Calanus finmarchicus, Calanus glacialis, Metridia longa, Oithona similis, Pseudocalanus spp., Microcalanus spp., and Microsetella norvegica) sampled using 64-µm mesh nets. Numerically, copepod nauplii (≥ 50%) and the young developmental stages of small copepods (< 2 mm prosome length as adult) dominated the samples. Three main patterns were identified: (1) large Calanus spp. were predominantly older copepodids CIV–CV, while (2) the small harpacticoid M. norvegica were adults. (3) For other species, all copepodid stages were present. Older copepodids and adults dominated populations of O. similis, Pseudocalanus spp. and M. longa. In Microcalanus spp., high proportion of young copepodids CI–CIII indicated active winter recruitment. We discuss the notion of winter as a developing and reproductive period for small copepods in light of observed age structures, presence of nauplii, and previous knowledge about the species. Lower predation risks during winter may, in part, explain why this season could be beneficial as a period for development. Winter may be a key season for development of small, omnivorous copepods in the Arctic, whereas large copepods such as Calanus spp. seems to be reliant on spring and summer for reproduction and development. [ABSTRACT FROM AUTHOR]