Unlocking the secret life of blue mussels: Exploring connectivity in the Skagerrak through biophysical modeling and population genomics.

Knowledge of functional dispersal barriers in the marine environment can be used to inform a wide variety of management actions, such as marine spatial planning, restoration efforts, fisheries regulations, and invasive species management. Locations and causes of dispersal barriers can be studied through various methods, including movement tracking, biophysical modeling, demographic models, and genetics. Combining methods illustrating potential dispersal, such as biophysical modeling, with realized dispersal through, e.g., genetic connectivity estimates, provides particularly useful information for teasing apart potential causes of observed barriers. In this study, we focus on blue mussels (Mytilus edulis) in the Skagerrak-a marginal sea connected to the North Sea in Northern Europe-and combine biophysical models of larval dispersal with genomic data to infer locations and causes of dispersal barriers in the area. Results from both methods agree; patterns of ocean currents are a major structuring factor in the area. We find a complex pattern of source-sink dynamics with several dispersal barriers and show that some areas can be isolated despite an overall high dispersal capability. Finally, we translate our finding into management advice that can be used to sustainably manage this ecologically and economically important species in the future.

Genome architecture and selective signals compensatorily shape plastic response to a new environment.

Transcriptional plasticity interacts with natural selection in complex ways and is crucial for the survival of species under rapid climate change. How 3D genome architecture affects transcriptional plasticity and its interaction with genetic adaptation are unclear. We transplanted estuarine oysters to a new environment and found that genes located in active chromatin regions exhibited greater transcriptional plasticity, and changes in these regions were negatively correlated with selective signals. This indicates a trade-off between 3D active regions and selective signals in shaping plastic responses to a new environment. Specifically, a mutation, lincRNA, and changes in the accessibility of a distal enhancer potentially affect its interaction with the ManⅡa gene, which regulates the muscle function and survival of oysters. Our findings reveal that 3D genome architecture compensates for the role of genetic adaptation in environmental response to new environments and provide insights into synergetic genetic and epigenetic interactions critical for fitness-related trait and survival in a model marine species.

Clones on the run: The genomics of a recently expanded partially clonal species.

Why species that in their core areas mainly reproduce sexually become enriched with clones in marginal populations ("geographic parthenogenesis") remains unclear. Earlier hypotheses have emphasized that selection might promote clonality because it protects locally adapted genotypes. On the other hand, it also hampers recombination and adaptation to changing conditions. The aim of the present study was to investigate the early stages of range expansion in a partially clonal species and what drives an increase in cloning during such expansion. We used genome-wide sequencing to investigate the origin and evolution of large clones formed in a macroalgal species (Fucus vesiculosus) during a recent expansion into the postglacial Baltic Sea. We found low but persistent clonality in core populations, while at range margins, large dominant clonal lineages had evolved repeatedly from different sexual populations. A range expansion model showed that even when asexual recruitment is less favourable than sexual recruitment in core populations, repeated bottlenecks at the expansion front can establish a genetically eroded clonal wave that spreads ahead of a sexual wave into the new area. Genetic variation decreases by drift following repeated bottlenecks at the expansion front. This results in the emerging clones having low expected heterozygosity, which corroborated our empirical observations. We conclude that Baker's Law (clones being favoured by uniparental reproductive assurance in new areas) can play an important role during range expansion in partially clonal species, resulting in a complex spatiotemporal mosaic of clonal and sexual lineages that might persist during thousands of generations.

A decade of progress in marine evolutionary biology.

This article summarizes the Evolutionary Applications Special Issue, "A decade of progress in Marine Evolutionary Biology." The globally connected ocean, from its pelagic depths to its highly varied coastlines, inspired Charles Darwin to develop the theory of evolution during the voyage of the Beagle. As technology has developed, there has been a dramatic increase in our knowledge about life on our blue planet. This Special Issue, composed of 19 original papers and seven reviews, represents a small contribution to the larger picture of recent research in evolutionary biology, and how such advancements come about through the connection of researchers, their fields, and their knowledge. The first European network for marine evolutionary biology, the Linnaeus Centre for Marine Evolutionary Biology (CeMEB), was developed to study evolutionary processes in the marine environment under global change. Though hosted by the University of Gothenburg in Sweden, the network quickly grew to encompass researchers throughout Europe and beyond. Today, more than a decade after its foundation, CeMEB's focus on the evolutionary consequences of global change is more relevant than ever, and knowledge gained from marine evolution research is urgently needed in management and conservation. This Special Issue, organized and developed through the CeMEB network, contains contributions from all over the world and provides a snapshot of the current state of the field, thus forming an important basis for future research directions.

Adaptive, maladaptive, neutral, or absent plasticity: Hidden caveats of reaction norms.

Adaptive phenotypic plasticity may improve the response of individuals when faced with new environmental conditions. Typically, empirical evidence for plasticity is based on phenotypic reaction norms obtained in reciprocal transplant experiments. In such experiments, individuals from their native environment are transplanted into a different environment, and a number of trait values, potentially implicated in individuals' response to the new environment, are measured. However, the interpretations of reaction norms may differ depending on the nature of the assessed traits, which may not be known beforehand. For example, for traits that contribute to local adaptation, adaptive plasticity implies nonzero slopes of reaction norms. By contrast, for traits that are correlated to fitness, high tolerance to different environments (possibly due to adaptive plasticity in traits that contribute to adaptation) may, instead, result in flat reaction norms. Here we investigate reaction norms for adaptive versus fitness-correlated traits and how they may affect the conclusions regarding the contribution of plasticity. To this end, we first simulate range expansion along an environmental gradient where plasticity evolves to different values locally and then perform reciprocal transplant experiments in silico. We show that reaction norms alone cannot inform us whether the assessed trait exhibits locally adaptive, maladaptive, neutral, or no plasticity, without any additional knowledge of the traits assessed and species' biology. We use the insights from the model to analyse and interpret empirical data from reciprocal transplant experiments involving the marine isopod Idotea balthica sampled from two geographical locations with different salinities, concluding that the low-salinity population likely has reduced adaptive plasticity relative to the high-salinity population. Overall, we conclude that, when interpreting results from reciprocal transplant experiments, it is necessary to consider whether traits assessed are locally adaptive with respect to the environmental variable accounted for in the experiments or correlated to fitness.

Beyond the genomes of Fulvia fulva (syn. Cladosporium fulvum) and Dothistroma septosporum: New insights into how these fungal pathogens interact with their host plants.

Fulvia fulva and Dothistroma septosporum are closely related apoplastic pathogens with similar lifestyles but different hosts: F. fulva is a pathogen of tomato, whilst D. septosporum is a pathogen of pine trees. In 2012, the first genome sequences of these pathogens were published, with F. fulva and D. septosporum having highly fragmented and near-complete assemblies, respectively. Since then, significant advances have been made in unravelling their genome architectures. For instance, the genome of F. fulva has now been assembled into 14 chromosomes, 13 of which have synteny with the 14 chromosomes of D. septosporum, suggesting these pathogens are even more closely related than originally thought. Considerable advances have also been made in the identification and functional characterization of virulence factors (e.g., effector proteins and secondary metabolites) from these pathogens, thereby providing new insights into how they promote host colonization or activate plant defence responses. For example, it has now been established that effector proteins from both F. fulva and D. septosporum interact with cell-surface immune receptors and co-receptors to activate the plant immune system. Progress has also been made in understanding how F. fulva and D. septosporum have evolved with their host plants, whilst intensive research into pandemics of Dothistroma needle blight in the Northern Hemisphere has shed light on the origins, migration, and genetic diversity of the global D. septosporum population. In this review, we specifically summarize advances made in our understanding of the F. fulva-tomato and D. septosporum-pine pathosystems over the last 10 years.

An Integrated Omics Approach Uncovers the Novel Effector Ecp20-2 Required for Full Virulence of Cladosporium fulvum on Tomato.

The fungus Cladosporium fulvum causes the leaf mould in tomatoes. During the colonization of the host, it secretes plenty of effector proteins into the plant apoplast to suppress the plant's immune system. Here, we characterized and functionally analyzed the Ecp20-2 gene of C. fulvum using combined omics approaches. RNA-sequencing of susceptible tomato plants inoculated with C. fulvum race 0WU showed strongly induced expression of the Ecp20-2 gene. Strong upregulation of expression of the Ecp20-2 gene was confirmed by qPCR, and levels were comparable to those of other known effectors of C. fulvum. The Ecp20-2 gene encodes a small secreted protein of 149 amino acids with a predicted signal peptide of 17 amino acids. Mass spectrometry of apoplastic fluids from infected tomato leaves revealed the presence of several peptides originating from the Ecp20-2 protein, indicating that the protein is secreted and likely functions in the apoplast. In the genome of C. fulvum, Ecp20-2 is surrounded by various repetitive elements, but no allelic variation was detected in the coding region of Ecp20-2 among 120 C. fulvum isolates collected in Japan. Δecp20-2 deletion mutants of strain 0WU of C. fulvum showed decreased virulence, supporting that Ecp20-2 is an effector required for full virulence of the fungus. Virulence assays confirmed a significant reduction of fungal biomass in plants inoculated with Δecp20-2 mutants compared to those inoculated with wild-type, Δecp20-2-complemented mutants, and ectopic transformants. Sequence similarity analysis showed the presence of Ecp20-2 homologs in the genomes of several Dothideomycete fungi. The Ecp20-2 protein shows the best 3D homology with the PevD1 effector of Verticillium dahliae, which interacts with and inhibits the activity of the pathogenesis-related protein PR5, which is involved in the immunity of several host plants.

Larval development in the Pacific oyster and the impacts of ocean acidification: Differential genetic effects in wild and domesticated stocks.

The adaptive capacity of marine calcifiers to ocean acidification (OA) is a topic of great interest to evolutionary biologists and ecologists. Previous studies have provided evidence to suggest that larval resilience to high pCO2 seawater for these species is a trait with a genetic basis and variability in natural populations. To date, however, it remains unclear how the selective effects of OA occur within the context of complex genetic interactions underpinning larval development in many of the most vulnerable taxa. Here we evaluated phenotypic and genetic changes during larval development of Pacific oysters (Crassostrea gigas) reared in ambient (~400 µatm) and high (~1600 µatm) pCO2 conditions, both in domesticated and naturalized "wild" oysters from the Pacific Northwest, USA. Using pooled DNA samples, we determined changes in allele frequencies across larval development, from early "D-stage" larvae to metamorphosed juveniles (spat), in both groups and environments. Domesticated larvae had ~26% fewer loci with changing allele frequencies across developmental stages and <50% as many loci affected by acidified culture conditions, compared to larvae from wild broodstock. Functional enrichment analyses of genetic markers with significant changes in allele frequency revealed that the structure and function of cellular membranes were disproportionately affected by high pCO2 conditions in both groups. These results indicate the potential for a rapid adaptive response of oyster populations to OA conditions; however, underlying genetic changes associated with larval development differ between these wild and domesticated oyster stocks and influence their adaptive responses to OA conditions.

Temporally balanced selection during development of larval Pacific oysters (Crassostrea gigas) inherently preserves genetic diversity within offspring.

Balancing selection is one of the mechanisms which has been proposed to explain the maintenance of genetic diversity in species across generations. For species with large populations and complex life histories, however, heterogeneous selection pressures may create a scenario in which the net effects of selection are balanced across developmental stages. With replicated cultures and a pooled sequencing approach, we show that genotype-dependent mortality in larvae of the Pacific oyster (Crassostrea gigas) is largely temporally dynamic and inconsistently in favour of a single genotype or allelic variant at each locus. Overall, the patterns of genetic change we observe to be taking place are more complex than what would be expected under classical examples of additive or dominant genetic interactions. They are also not easily explained by our current understanding of the effects of genetic load. Collectively, temporally heterogeneous selection pressures across different larval developmental stages may act to maintain genetic diversity, while also inherently sheltering genetic load within oyster populations.

Climate change driven hyposalinity as a selective agent in the littoral mesoherbivore Idotea balthica.

Climate change will include a decrease in seawater salinity in the Baltic Sea. We quantified the effects of the projected future desalination on survival of the early life stage of the littoral herbivore Idotea balthica. We collected egg-bearing Idotea from three range-margin Baltic Sea populations, we exposed half of each brood to either current (6‰) or future salinity (3.5‰). We genotyped a subsample of each brood to analyse patterns of allelic change and to identify genomic regions targeted by selection. The survival was overall reduced by hyposalinity and broods varied in response to hyposalinity implying genetic variation in tolerance, with a stronger decrease in genetic diversity in future salinity. Finally, we identified proteins with crucial roles in basic cellular functions. This study indicates that projected future northern Baltic Sea hyposalinity will not just hamper I. balthica survival, but its selective pressure may also affect genetic diversity and cell physiology.

Spatial genetic structure in a crustacean herbivore highlights the need for local considerations in Baltic Sea biodiversity management.

Incorporating species' eco-evolutionary responses to human-caused disturbances remains a challenge in marine management efforts. A prerequisite is knowledge of geographic structure and scale of genetic diversity and connectivity-the so-called seascape genetic patterns. The Baltic Sea is an excellent model system for studies linking seascape genetics with effects of anthropogenic stress. However, seascape genetic patterns in this area are only described for a few species and are completely unknown for invertebrate herbivores, which constitute a critical part of the ecosystem. This information is crucial for sustainable management, particularly under future scenarios of rapid environmental change. Here, we investigate the population genetic structure among 31 locations throughout the Baltic Sea, of which 45% were located in marine protected areas, in one of the most important herbivores of this region, the isopod crustacean Idotea balthica, using an array of 33,774 genome-wide SNP markers derived from 2b-RAD sequencing. In addition, we generate a biophysical connectivity matrix for I. balthica from a combination of oceanographic current models and estimated life history traits. We find population structure on scales of hundreds of kilometers across the Baltic Sea, where genomic patterns in most cases closely match biophysical connectivity, indicating passive transport with oceanographic currents as an important mean of dispersal in this species. We also find a reduced genetic diversity in terms of heterozygosity along the main salinity gradient of the Baltic Sea, suggesting periods of low population size. Our results provide crucial information for the management of a key ecosystem species under expected changes in temperature and salinity following global climate change in a marine coastal area.

A conserved GH17 glycosyl hydrolase from plant pathogenic Dothideomycetes releases a DAMP causing cell death in tomato.

To facilitate infection, pathogens deploy a plethora of effectors to suppress basal host immunity induced by exogenous microbe-associated or endogenous damage-associated molecular patterns (DAMPs). In this study, we have characterized family 17 glycosyl hydrolases of the tomato pathogen Cladosporium fulvum (CfGH17) and studied their role in infection. Heterologous expression of CfGH17-1 to 5 by potato virus X in different tomato cultivars showed that CfGH17-1 and CfGH17-5 enzymes induce cell death in Cf-0, Cf-1 and Cf-5 but not in Cf-Ecp3 tomato cultivars or tobacco. Moreover, CfGH17-1 orthologues from other phytopathogens, including Dothistroma septosporum and Mycosphaerella fijiensis, also trigger cell death in tomato. CfGH17-1 and CfGH17-5 are predicted to be ß-1,3-glucanases and their enzymatic activity is required for the induction of cell death. CfGH17-1 hydrolyses laminarin, a linear 1,3-ß-glucan with 1,6-ß linkages. CfGH17-1 expression is down-regulated during the biotrophic phase of infection and up-regulated during the necrotrophic phase. Deletion of CfGH17-1 in C. fulvum did not reduce virulence on tomato, while constitutive expression of CfGH17-1 decreased virulence, suggesting that abundant presence of CfGH17-1 during biotrophic growth may release a DAMP that activates plant defence responses. Under natural conditions CfGH17-1 is suggested to play a role during saprophytic growth when the fungus thrives on dead host tissue, which is in line with its high levels of expression at late stages of infection when host tissues have become necrotic. We suggest that CfGH17-1 releases a DAMP from the host cell wall that is recognized by a yet unknown host plant receptor.

Factors affecting formation of adventitious branches in the seaweeds Fucus vesiculosus and F. radicans.

BACKGROUND: In the brackish Baltic Sea, shedding of adventitious branches is central to asexual recruitment of new thalli in the brown algae Fucus vesiculosus and F. radicans. To test which factors influence the formation of adventitious branches in brackish and in more marine conditions, we sampled 29 Fucus sites in the Baltic Sea (salinity 3-11) and 18 sites from the Danish straits, Kattegat, Skagerrak, and the North Sea (salinity 15-35). Separately for each area, we used structural equation modelling to determine which of eight predictor factors (phosphate, nitrate, chlorophyll-a (as a proxy for turbidity), temperature, salinity, oxygen, grazing pressure, and thallus area) best explained observed numbers of adventitious branches. RESULTS: In more marine waters, high yearly average values of phosphate, salinity and turbidity had positive effects on the formation of adventitious branches. In brackish-waters, however, high numbers of adventitious branches were found in areas with low yearly average values of temperature, salinity and oxygen. Grazing intensity had no significant effect in either of the two study areas, contrasting findings from studies in other areas. In areas with both sexually and asexually reproducing Fucus individuals, clones had on average more adventitious branches than unique genotypes, although there was strong variation among clonal lineages. CONCLUSION: This study is the first to investigate multiple potential drivers of formation of adventitious branches in natural populations of Fucus. Our results suggest that several different factors synergistically and antagonistically affect the growth of adventitious branches in a complex way, and that the same factor (salinity) can have opposing effects in different areas.

"CATAStrophy," a Genome-Informed Trophic Classification of Filamentous Plant Pathogens - How Many Different Types of Filamentous Plant Pathogens Are There?

The traditional classification of fungal and oomycete phytopathogens into three classes - biotrophs, hemibiotrophs, or necrotrophs - is unsustainable. This study highlights multiple phytopathogen species for which these labels have been inappropriately applied. We propose a novel and reproducible classification based solely on genome-derived analysis of carbohydrate-active enzyme (CAZyme) gene content called CAZyme-Assisted Training And Sorting of -trophy (CATAStrophy). CATAStrophy defines four major divisions for species associated with living plants. These are monomertrophs (Mo) (corresponding to biotrophs), polymertrophs (P) (corresponding to necrotrophs), mesotrophs (Me) (corresponding to hemibiotrophs), and vasculartrophs (including species commonly described as wilts, rots, or anthracnoses). The Mo class encompasses symbiont, haustorial, and non-haustorial species. Me are divided into the subclasses intracellular and extracellular Me, and the P into broad and narrow host sub-classes. This gives a total of seven discrete plant-pathogenic classes. The classification provides insight into the properties of these species and offers a facile route to develop control measures for newly recognized diseases. Software for CATAStrophy is available online at https://github.com/ccdmb/catastrophy. We present the CATAStrophy method for the prediction of trophic phenotypes based on CAZyme gene content, as a complementary method to the traditional tripartite "biotroph-hemibiotroph-necrotroph" classifications that may encourage renewed investigation and revision within the fungal biology community.

Ecological and functional consequences of coastal ocean acidification: Perspectives from the Baltic-Skagerrak System.

Ocean temperatures are rising; species are shifting poleward, and pH is falling (ocean acidification, OA). We summarise current understanding of OA in the brackish Baltic-Skagerrak System, focussing on the direct, indirect and interactive effects of OA with other anthropogenic drivers on marine biogeochemistry, organisms and ecosystems. Substantial recent advances reveal a pattern of stronger responses (positive or negative) of species than ecosystems, more positive responses at lower trophic levels and strong indirect interactions in food-webs. Common emergent themes were as follows: OA drives planktonic systems toward the microbial loop, reducing energy transfer to zooplankton and fish; and nutrient/food availability ameliorates negative impacts of OA. We identify several key areas for further research, notably the need for OA-relevant biogeochemical and ecosystem models, and understanding the ecological and evolutionary capacity of Baltic-Skagerrak ecosystems to respond to OA and other anthropogenic drivers.

Diet-dependent gene expression highlights the importance of Cytochrome P450 in detoxification of algal secondary metabolites in a marine isopod.

Isopods of the genus Idotea have an unusual ability to feed on algae containing high amounts of chemical defense molecules, such as species of the genera Fucus and Ulva. In this study, we compared gene expression patterns of Idotea balthica individuals fed with Fucus vesiculosus to individuals fed with Ulva lactuca. We generated the first-ever transcriptome assembly for this species, and found 3,233 differentially expressed genes across feeding regimes. However, only a handful of biological functions were enriched with regard to differentially expressed genes, the most notable being "alkaloid metabolic process". Within this category, we found eight differentially expressed cytochrome P450 (CYP) unigenes, all of which had a higher expression in the U. lactuca diet treatment. A phylogenetic analysis showed that the differentially expressed CYP genes are closely related to a CYP gene described from the hepatopancreas of the spiny lobster Panulirus argus, and we hypothesize that these transcripts are involved in metabolite detoxification. This is a first step in the understanding of this algae-grazer interaction, and will form a basis for future work to characterize cytochrome P450 functioning in marine crustaceans.

Divergence and plasticity shape adaptive potential of the Pacific oyster.

The interplay between divergence and phenotypic plasticity is critical to our understanding of a species' adaptive potential under rapid climate changes. We investigated divergence and plasticity in natural populations of the Pacific oyster Crassostrea gigas with a congeneric oyster Crassostrea angulata from southern China used as an outgroup. Genome re-sequencing of 371 oysters revealed unexpected genetic divergence in a small area that coincided with phenotypic divergence in growth, physiology, heat tolerance and gene expression across environmental gradients. These findings suggest that selection and local adaptation are pervasive and, together with limited gene flow, influence population structure. Genes showing sequence differentiation between populations also diverged in transcriptional response to heat stress. Plasticity in gene expression is positively correlated with evolved divergence, indicating that plasticity is adaptive and favoured by organisms under dynamic environments. Divergence in heat tolerance-partly through acetylation-mediated energy depression-implies differentiation in adaptive potential. Trade-offs between growth and survival may play an important role in local adaptation of oysters and other marine invertebrates.

Stress and sexual reproduction affect the dynamics of the wheat pathogen effector AvrStb6 and strobilurin resistance.

Host resistance and fungicide treatments are cornerstones of plant-disease control. Here, we show that these treatments allow sex and modulate parenthood in the fungal wheat pathogen Zymoseptoria tritici. We demonstrate that the Z. tritici-wheat interaction complies with the gene-for-gene model by identifying the effector AvrStb6, which is recognized by the wheat resistance protein Stb6. Recognition triggers host resistance, thus implying removal of avirulent strains from pathogen populations. However, Z. tritici crosses on wheat show that sex occurs even with an avirulent parent, and avirulence alleles are thereby retained in subsequent populations. Crossing fungicide-sensitive and fungicide-resistant isolates under fungicide pressure results in a rapid increase in resistance-allele frequency. Isolates under selection always act as male donors, and thus disease control modulates parenthood. Modeling these observations for agricultural and natural environments reveals extended durability of host resistance and rapid emergence of fungicide resistance. Therefore, fungal sex has major implications for disease control.

Gene expression correlated with delay in shell formation in larval Pacific oysters (Crassostrea gigas) exposed to experimental ocean acidification provides insights into shell formation mechanisms.

BACKGROUND: Despite recent work to characterize gene expression changes associated with larval development in oysters, the mechanism by which the larval shell is first formed is still largely unknown. In Crassostrea gigas, this shell forms within the first 24 h post fertilization, and it has been demonstrated that changes in water chemistry can cause delays in shell formation, shell deformations and higher mortality rates. In this study, we use the delay in shell formation associated with exposure to CO2-acidified seawater to identify genes correlated with initial shell deposition. RESULTS: By fitting linear models to gene expression data in ambient and low aragonite saturation treatments, we are able to isolate 37 annotated genes correlated with initial larval shell formation, which can be categorized into 1) ion transporters, 2) shell matrix proteins and 3) protease inhibitors. Clustering of the gene expression data into co-expression networks further supports the result of the linear models, and also implies an important role of dynein motor proteins as transporters of cellular components during the initial shell formation process. CONCLUSIONS: Using an RNA-Seq approach with high temporal resolution allows us to identify a conceptual model for how oyster larval calcification is initiated. This work provides a foundation for further studies on how genetic variation in these identified genes could affect fitness of oyster populations subjected to future environmental changes, such as ocean acidification.

Contrasting physiological responses to future ocean acidification among Arctic copepod populations.

Widespread ocean acidification (OA) is modifying the chemistry of the global ocean, and the Arctic is recognized as the region where the changes will progress at the fastest rate. Moreover, Arctic species show lower capacity for cellular homeostasis and acid-base regulation rendering them particularly vulnerable to OA. In the present study, we found physiological differences in OA response across geographically separated populations of the keystone Arctic copepod Calanus glacialis. In copepodites stage CIV, measured reaction norms of ingestion rate and metabolic rate showed severe reductions in ingestion and increased metabolic expenses in two populations from Svalbard (Kongsfjord and Billefjord) whereas no effects were observed in a population from the Disko Bay, West Greenland. At pHT 7.87, which has been predicted for the Svalbard west coast by year 2100, these changes resulted in reductions in scope for growth of 19% in the Kongsfjord and a staggering 50% in the Billefjord. Interestingly, these effects were not observed in stage CV copepodites from any of the three locations. It seems that CVs may be more tolerant to OA perhaps due to a general physiological reorganization to meet low intracellular pH during hibernation. Needless to say, the observed changes in the CIV stage will have serious implications for the C. glacialis population health status and growth around Svalbard. However, OA tolerant populations such as the one in the Disko Bay could help to alleviate severe effects in C. glacialis as a species.