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Accurate species identification is the cornerstone of any ecological study--yet this fundamental step is not always possible for marine zooplankton. Routine species' identification, especially of juvenile andlarval stages, is difficult for Calanus species (Copepoda; Calanoida) in the N. Atlantic Ocean, were two or three species may co-occur.

Estimates of carbon flux to the deep oceans are essential for our understanding of global carbon budgets. Sinking of detrital material (“biological pump”) is usually thought to be the main biological component of this flux. Here, we identify an additional biological mechanism, the seasonal “lipid pump,” which is highly efficient at sequestering carbon into the deep ocean. It involves the vertical transport and metabolism of carbon rich lipids by overwintering zooplankton. We show that one species, the copepodCalanus finmarchicusoverwintering in the North Atlantic, sequesters an amount of carbon equivalent to the sinking flux of detrital material. The efficiency of the lipid pump derives from a nearcomplete decoupling between nutrient and carbon cycling—a “lipid shunt,” and its direct transport of carbon through the mesopelagic zone to below the permanent thermocline with very little attenuation. Inclusion of the lipid pump almost doubles the previous estimates of deep-ocean carbon sequestration by biological processes in the North Atlantic.

Copepods of the zooplankton genus Calanus play a key role in marine ecosystems in the northern seas. Although being among the most studied organisms on Earth, due to their ecological importance, genomic resources for Calanus spp. remain scarce, mostly due to their large genome size (from 6 to 12 Gbps). As an alternative to whole‐genome sequencing in Calanus spp., we sequenced and de novo assembled transcriptomes of five Calanus species: Calanus glacialis, C. hyperboreus, C. marshallae, C. pacificus, and C. helgolandicus. Functional assignment of protein families based on clusters of orthologous genes (COG) and gene ontology (GO) annotations showed analogous patterns of protein functions across species. Phylogenetic analyses using maximum likelihood (ML) of 191 protein‐coding genes mined from RNA‐seq data fully resolved evolutionary relationships among seven Calanus species investigated (five species sequenced for this study and two species with published datasets), with gene and site concordance factors showing that 109 out of 191 protein‐coding genes support a separation between three groups: the C. finmarchicus group (including C. finmarchicus, C. glacialis, and C. marshallae), the C. helgolandicus group (including C. helgolandicus, C. sinicus, and C. pacificus) and the monophyletic C. hyperboreus group. The tree topology obtained in ML analyses was similar to a previously proposed phylogeny based on morphological criteria and cleared certain ambiguities from past studies on evolutionary relationships among Calanus species. This study contributes and improve the currently available transcriptomic resources for Calanus spp. and explore de novo transcriptome data as an alternative to whole genome sequencing to infer evolutionary relationships within the genus Calanus. Here, we sequenced, assembled, and annotated de novo transcriptomes of two species for the first time (C. hyperboreus and C. marshallae), and three species with some but limited transcriptomic data available (C. glacialis, C. helgolandicus, and C. pacificus).

Calanus oil (COil) is a natural product extracted from marine zooplankton Calanus finmarchicus found in the North Atlantic Ocean. This oil is rich in wax esters of polyunsaturated fatty acids (PUFAs) and has been projected as the best alternative to fish oil because its production cannot keep pace with the demands from the growing markets. The COil is the only commercially available marine source of wax esters, whereas classic ω-3 PUFAs comes from triglycerides, ethyl esters, and phospholipids. It has, in recent decades, been seen that there is an unprecedented rise in the use of PUFA-rich oil in the aquaculture industry. A simultaneous rise in the demand of PUFAs is also observed in the health care industry, where PUFAs are suggested preventing various disorders related to lifestyles such as obesity, diabetes mellitus, chronic low-grade inflammation, atherosclerosis, and brain and cardiovascular disorders (CVDs). In this review, we will explore the metabolic aspects related to the use of COil as an antioxidant, anticholesterinemic, and anti-inflammatory dietary source and its impact on the prevention and therapy of obesity-related metabolic disorders.

Adult males of Calanus copepods in the Arctic are mainly observed between late autumn and late spring, and are seldom recorded during summer. Due to logistical constraints, there are still relatively few studies on zooplankton in high-latitude regions during the winter, and subsequently, little is known about Calanus males. Here, we present data on abundance, spatial distribution, prosome length, lipid content, respiration and swimming activity of Calanus adults, along with adult sex ratios in Calanus populations from 5 Arctic fjords in Svalbard, Norway (78−80° N) during the polar night in January 2015, 2016 and 2017. Adult males and females of Calanus were observed at all locations and occurred throughout the entire water column. Morphological examination and molecular identification of Calanus males proved that all males encountered belong to Calanus glacialis, even in the fjords where overwintering copepodite stage CV of C. finmarchicus dominated at the time. Adult sex ratios in C. glacialis populations varied from 1 male per 4 females to 2 males per female. From 3 to 18% of females carried spermatophores attached to the genital segment. Lipid content in males was slightly higher than in females. Shipboard experiments showed that males had higher swimming activity and respiration rates than females. Our observations indicate that adult males of C. glacialis stay active and demonstrate active mating behavior in mid-winter, and that the mating phenology of C. glacialis is decoupled from that of C. finmarchicus in the study area in January.

The discrimination and taxonomic identification of marine species continues to pose a challenge despite the growing number of diagnostic metrics and approaches. This study examined the genetic relationship between two sibling species of the genus Calanus (Crustacea; Copepoda; Calanidae), C. agulhensis and C. sinicus, using a multi-gene analysis. DNA sequences were determined for portions of the mitochondrial cytochrome c oxidase I (mtCOI); nuclear citrate synthase (CS), and large subunit (28S) rRNA genes for specimens collected from the Sea of Japan and North East (NE) Pacific Ocean for C. sinicus and from the Benguela Current and Agulhas Bank, off South Africa, for C. agulhensis. For mtCOI, C. sinicus and C. agulhensis showed similar levels of haplotype diversity (H(d) = 0.695 and 0.660, respectively) and nucleotide diversity (π = 0.003 and 0.002, respectively). Pairwise F(ST) distances for mtCOI were significant only between C. agulhensis collected from the Agulhas and two C. sinicus populations: the Sea of Japan (F(ST) = 0.152, p<0.01) and NE Pacific (F(ST) = 0.228, p<0.005). Between the species, F(ST) distances were low for both mtCOI (F(ST) = 0.083, p = 0.003) and CS (F(ST) = 0.050, p = 0.021). Large subunit (28S) rRNA showed no variation between the species. Our results provide evidence of the lack of genetic distinction of C. sinicus and C. agulhensis, raise questions of whether C. agulhensis warrants status as a distinct species, and indicate the clear need for more intensive and extensive ecological and genetic analysis.

The Saguenay-St. Lawrence Marine Park (SSLMP) is a region that sustains a high abundance of zooplankton. The connectivity between zooplankton populations within the SSLMP and the surrounding areas was investigated for Calanus finmarchicus and C. hyperboreus. Deep-dwelling stage V copepodites (CVs) were collected in the Marine Park as well as in putative source regions in the St. Lawrence system in July 2009 (a time when they were entering into diapause). In May 2010, at the end of the overwintering period, diapausing CVs were sampled again in the Marine Park. To discriminate the origins and to predict the probable regions of origin of these deep-dwelling diapausing CVs in the SSLMP, a quadratic discriminant function analysis (QDFA) was performed. The classification algorithm was based on the carbon isotopic composition ( delta super(13)C) and percent carbon (%C) of individual copepods, as these variables are conservative when lipids are extracted prior to analysis. Our results suggest that about 23% of the Calanus spp. population sampled in SSLMP in late spring 2010 originated from the Saguenay Fjord (inside the SSLMP). The remainder of this population originated from regions outside the SSLMP, including the Lower St. Lawrence Estuary, and likely further east in the Gulf of St. Lawrence. Our results revealed high connectivity across the Saguenay and the St. Lawrence systems, as well as the potential for significant local production and recruitment of Calanus spp. within the Saguenay Fjord. This study also revealed the effectiveness of using delta super(13)C as a marker in delineating the origin of Calanusspp., which has a relatively long non-feeding overwintering and diapausing period making it amenable to the conservation of isotopic signatures.

Arctic Cod ( Boreogadus saida ) occur throughout the circumpolar north; however, their distributions at localized scales are not well understood. The seasonal habitat associations and diet preferences across life-history stages of this keystone species are also poorly known, thereby impeding effective regulatory efforts in support of conservation objectives. The distribution of Arctic Cod in the Canadian Beaufort Sea was assessed using bottom trawling in shelf and slope habitats between 20 and 1000 m depths. Highest catch biomasses occurred at 350 and 500 m depth slope stations, coinciding with >0 °C temperatures in the Pacific–Atlantic thermohalocline and Atlantic water mass. Calanus glacialis , Calanus hyperboreus , Themisto libellula , and Themisto abyssorum were identified as key prey species in the diet of Arctic Cod, comprising approximately 86 % of total biomass in guts. Hierarchical cluster analysis with a SIMPROF test identified five statistically significant ( p  < 0.05) diet groups among gut samples. Arctic Cod shifted from a primarily Calanus diet at shelf stations (<200 m depth) to a Themisto diet in slope habitats (>200 m depth) coinciding with an associated increase in fish standard length with depth. Smaller Arctic Cod fed primarily on Calanus copepods and larger Arctic Cod fed primarily on the larger Themisto species. The habitat and diet associations presented here will inform knowledge of structural and functional relationships in Arctic marine ecosystems, aid in mitigation and conservation efforts, and will enhance our ability to predict the effects of climate change on the local spatial and depth associations of this pivotal marine fish.

Seasonal occurrences of Calanus sinicus and Calanus jashnovi were investigated using monthly samples covering 0–200 or 0–1000 m in central Sagami Bay, Japan, from May 2002 to January 2004. While copepodite stages I–V (CI–CV) of C. sinicus appeared at 0–200 m throughout the year, significant fractions of the CVs occurred below 200 m during spring–autumn, then disappeared in winter. The adults (CVIs) occurred at 0–200 m throughout the year, although they were also abundant below 200 m during autumn–winter. Respiration rates and carbon contents of C. sinicus were measured in July 2007, revealing that the mesopelagic CVs had lower oxygen consumption and higher carbon contents than those in the epipelagic CV–CVIs. These results indicate that C. sinicus has two ecologically-distinct populations in Sagami Bay: one exists in the epipelagic zone throughout the year, while the other diapauses at CV in the mesopelagic zone during spring–autumn and matures in winter. The C. jashnovi CVs occurred below 600 m in spring–autumn, while the CVIs occurred at 200–400 m during winter and the CI–CIVs occurred at 0–200 m during winter–spring. The lower abundance of the CI–CIVs and CVIs compared to the CVs imply that the C. jashnovi reproduced outside of the bay and were occasionally transported into the bay.

To better predict ecological consequences of changing Arctic sea ice environments, we aimed to quantify the contribution of ice algae-produced carbon (α Ice) to pelagic food webs in the central Arctic Ocean. Eight abundant under-ice fauna species were submitted to fatty acid (FA) analysis, bulk stable isotope analysis (BSIA) of nitrogen (δ 15N) and carbon (δ 13C) isotopic ratios, and compound-specific stable isotope analysis (CSIA) of δ 13C in trophic marker FAs. A high mean contribution α Ice was found in Apherusa glacialis and other sympagic (ice-associated) amphipods (BSIA: 87% to 91%, CSIA: 58% to 92%). The pelagic copepods Calanus glacialis and C. hyperboreus, and the pelagic amphipod Themisto libellula showed substantial, but varying α Ice values (BSIA: 39% to 55%, CSIA: 23% to 48%). Lowest α Ice mean values were found in the pteropod Clione limacina (BSIA: 30%, CSIA: 14% to 18%). Intra-specific differences in FA compositions related to two different environmental regimes were more pronounced in pelagic than in sympagic species. A comparison of mixing models using different isotopic approaches indicated that a model using δ 13C signatures from both diatomspecific and dinoflagellate-specific marker FAs provided the most conservative estimate of α Ice. Our results imply that ecological key species of the central Arctic Ocean thrive significantly on carbon synthesized by ice algae. Due to the close connectivity between sea ice and the pelagic food web, changes in sea ice coverage and ice algal production will likely have important consequences for food web functioning and carbon dynamics of the pelagic system.