Magnus Lucassen

Hypoxia and hypercapnia often accompany seawater warming and interactively alter marine ectotherm performance, potentially threatening their populations. To detail mechanistic responses, we investigated whole-animal physiology alongside cellular homeostasis in a species expected to be relatively robust to their impacts, the oyster Ostrea edulis. Acute warming alone and combined with hypercapnia and hypoxia (deadly trio, DT) started at 18°C, increasing stepwise by 2°C per 48 h until critical temperature was reached (34°C). Death of oysters started at a lower temperature under DT than under acute warming alone, but rates equalized by 34°C. Hemolymph PO2 in DT-exposed oysters was 29% lower at 18°C, but by 34°C, was only slightly lower than that in oysters subjected to acute warming alone. In both groups, resting metabolic rate (RMR) and heart rate rose with warming. Hemolymph PO2 was stable until 26°C, whence it declined. DT elicited a higher heart rate, which began to fall after ∼32°C, whereas heart rate in oysters subjected to acute warming continued rising. Relative increases in branchial metabolite levels of alanine and fumarate, profiled via 1H-NMR spectroscopy, indicated greater contributions of anaerobic metabolism in DT-exposed oysters. Gill tissue showed higher levels of the mitochondrial stabilizer sirtuin-5 (SIRT5) alongside higher antioxidative capacity under DT compared with acute warming, before declining at temperatures beyond 30°C. Muscle intracellular pH, gill heat shock protein 70 and metabolic profiles appeared unaffected by DT compared with warming alone. Our results suggest that DT places an additional energetic burden on the oyster, lowering the critical temperature. Nevertheless, tolerance patterns indicate resilience to DT, which may require a rebalancing of passive tolerance mechanisms, especially metabolic depression.

Understanding population connectivity in the marine realm is crucial for conserving biodiversity, managing fisheries, and predicting species responses to environmental change. This is particularly important in Antarctic waters, where unique evolutionary histories and extreme conditions shape marine biodiversity. The longfin icedevil Aethotaxis mitopteryx is an elusive notothenioid fish endemic to Antarctic waters. To explore population connectivity in A. mitopteryx , we used RAD‐seq to investigate the genetic differentiation of two populations, one from the Eastern Weddell Sea and the other from the Eastern Antarctic Peninsula, two regions of ecological relevance greatly impacted by climate change. Despite spatial separation, analyses revealed no significant genetic differentiation between the two populations, suggesting extensive gene flow. A pronounced genetic distinction was, however, observed between males and females. This differentiation was largely localized to a specific chromosome, implying a genetic sex determination system with males being the heterogametic sex. These findings contribute novel insights into the genetic structure of A. mitopteryx populations and expand our understanding of genetic mechanisms in Antarctic fish. This study provides a foundation for further investigations into the evolutionary and ecological implications of sex chromosome differentiation in extreme environments.

Information on connectivity and genetic structure of marine organisms remains sparse in frontier ecosystems such as the Arctic Ocean. Filling these knowledge gaps becomes increasingly urgent, as the Arctic is undergoing rapid physical, ecological and socio‐economic changes. The abundant and widely distributed polar cod (Boreogadus saida) is highly adapted to Arctic waters, and its larvae and juveniles live in close association with sea ice. Through a reduced‐representation sequencing approach, this study explored the spatial genetic structure of polar cod at a circum‐Arctic scale. Genomic variation was partitioned into neutral and adaptive components to respectively investigate genetic connectivity and local adaptation. Based on 922 high‐quality single nucleotide polymorphism (SNP) markers genotyped in 611 polar cod, broad‐scale differentiation was detected among three groups: (i) Beaufort –Chukchi seas, (ii) all regions connected by the Transpolar Drift, ranging from the Laptev Sea to Iceland, including the European Arctic and (iii) West Greenland. Patterns of neutral genetic structure suggested broadscale oceanographic and sea ice drift features (i.e., Beaufort Gyre and Transpolar Drift) as important drivers of connectivity. Genomic variation at 35 outlier loci indicated adaptive divergence of the West Greenland and the Beaufort–Chukchi Seas populations, possibly driven by environmental conditions. Sea ice decline and changing ocean currents can alter or disrupt connectivity between polar cod from the three genetic groups, potentially undermining their resilience to climate change, even in putative refugia, such as the Central Arctic Ocean and the Arctic Archipelago.

Predicting anthropogenic impacts on benthic marine ecosystems is of great importance for conservation. Climate change models have indicated that increasing seawater temperatures will drive shifts in the distribution of benthic organisms due to species‐specific thermal tolerances. When combined with other stressors such as pollutants, interactive effects may lead to even greater impacts. Microplastics (MP), as a marine pollutant, have been shown to elicit responses in organisms but often at concentrations far greater than experienced in the environment and with short‐term exposure times. Assessing long‐term interactive effects of MP pollution and ocean warming on benthic marine organisms has not been previously addressed. A unique mesocosm facility was constructed on the island of Helgoland, in the southern North Sea, to explore the combined impacts of these two factors. The multi‐factorial experimental system is composed of 16 independent benthic mesocosms, utilizing novel features and methods for the continuous generation of climate change and MP exposure scenarios, while retaining natural conditions for other environmental parameters. We provide a description of the system design and methods, followed by an operational performance assessment during a 10‐month exposure experiment with European flat oysters (Ostrea edulis), evaluated on the accuracy of exposure scenario control and the degree of realism achieved. We demonstrate the novel application of kinetic modeling for generating environmentally relevant MP exposure conditions (+ 25 MP L⁻¹), and highlight the mesocosm systems suitability for studying chronic effects of MP pollution and ocean warming on benthic marine ecosystems through its real‐world application.

Photosynthesis is one of the most important biological processes on Earth, providing the main source of bioavailable energy, carbon, and oxygen via the use of sunlight. Despite this importance, the minimum light level sustaining photosynthesis and net growth of primary producers in the global ocean is still unknown. Here, we present measurements from the MOSAiC field campaign in the central Arctic Ocean that reveal the resumption of photosynthetic growth and algal biomass buildup under the ice pack at a daily average irradiance of not more than 0.04 ± 0.02 µmol photons m⁻² s⁻¹ in late March. This is at least one order of magnitude lower than previous estimates (0.3–5 µmol photons m⁻² s⁻¹) and near the theoretical minimum light requirement of photosynthesis (0.01 µmol photons m⁻² s⁻¹). Our findings are based on measurements of the temporal development of the under-ice light field and concurrent measurements of both chlorophyll a concentrations and potential net primary production underneath the sea ice at 86 °N. Such low light requirements suggest that euphotic zones where photosynthesis can occur in the world’s oceans may extend further in depth and time, with major implications for global productivity estimates.

Background: This study was part of a larger comprehensive project (BIOACID) addressing the physiological resilience of Polar cod, Boreogadus saida, to ocean acidification and global warming and aimed to unravel underlying molecular mechanisms of the observed physiological responses. Methods: Fish were acclimated long-term to three CO₂ concentrations comprising control conditions (390 ppm) and two projected climate scenarios (780 ppm and 1170 ppm). Each CO₂ treatment was combined with four temperatures: 0, 3, 6, and 8 °C. Here, we focused on the hepatic transcriptomic profiles from these previously physiologically characterized fish. Results: Generally, we did not detect signs of a classical stress response. Consistent with functional observations, warming induced much stronger molecular responses compared to elevated PCO₂, but an interaction between both factors existed to some extent. Gene ontology analysis revealed a strong response in lipid, amino acid, and protein metabolism. With increasing temperature, we observed a shift away from lipid metabolism, while carbohydrate metabolic pathways remained stable. Conclusions: Although we found Polar cod to be quite resilient to ocean acidification, temperature will remain a critical parameter for this valuable Arctic keystone species, and the question remains as to whether the observed acclimation strategies can be implemented in its natural habitat, especially when food supply is limited.

Polar ecosystems are experiencing amongst the most rapid rates of regional warming on Earth. Here, we discuss ‘omics’ approaches to investigate polar biodiversity, including the current state of the art, future perspectives and recommendations. We propose a community road map to generate and more fully exploit multi-omics data from polar organisms. These data are needed for the comprehensive evaluation of polar biodiversity and to reveal how life evolved and adapted to permanently cold environments with extreme seasonality. We argue that concerted action is required to mitigate the impact of warming on polar ecosystems via conservation efforts, to sustainably manage these unique habitats and their ecosystem services, and for the sustainable bioprospecting of novel genes and compounds for societal gain.

Protein turnover is highly energy consuming and overall relates to an organism’s growth performance varying largely between species, e.g., due to pre-adaptation to environmental characteristics such as temperature. Here, we determined protein synthesis rates and capacity of protein degradation in white muscle of the cold stenothermal Antarctic eelpout (Pachycara brachycephalum) and its closely related temperate counterpart, the eurythermal common eelpout (Zoarces viviparus). Both species were exposed to acute warming (P. brachycephalum, 0 °C + 2 °C day⁻¹; Z. viviparus, 4 °C + 3 °C day⁻¹). The in vivo protein synthesis rate (Ks) was monitored after injection of ¹³C-phenylalanine, and protein degradation capacity was quantified by measuring the activity of cathepsin D in vitro. Untargeted metabolic profiling by nuclear magnetic resonance (NMR) spectroscopy was used to identify the metabolic processes involved. Independent of temperature, the protein synthesis rate was higher in P. brachycephalum (Ks = 0.38–0.614 % day⁻¹) than in Z. viviparus (Ks= 0.148–0.379% day⁻¹). Whereas protein synthesis remained unaffected by temperature in the Antarctic species, protein synthesis in Z. viviparus increased to near the thermal optimum (16 °C) and tended to fall at higher temperatures. Most strikingly, capacities for protein degradation were about ten times higher in the Antarctic compared to the temperate species. These differences are mirrored in the metabolic profiles, with significantly higher levels of complex and essential amino acids in the free cytosolic pool of the Antarctic congener. Together, the results clearly indicate a highly cold-compensated protein turnover in the Antarctic eelpout compared to its temperate confamilial. Constant versus variable environments are mirrored in rigid versus plastic functional responses of the protein synthesis machinery.

The globin protein superfamily has diverse functions. Haemoglobin has been found in non-erythroid locations, including within the mitochondria. Using co-immunoprecipitation and in silico methods, we investigated the interaction of mitochondrial haemoglobin with ATP synthase and its associated proteins, including inhibitory factor 1 (IF1). We measured the expression of mitochondrial haemoglobin in response to hypoxia. In vitro and in silico evidence of interactions between mitochondrial haemoglobin and ATP synthase were found, and we report upregulated mitochondrial haemoglobin expression in response to hypoxia within skeletal muscle tissue. Our observations indicate that mitochondrial pH and ATP synthase activity are implicated in the mitochondrial haemoglobin response to hypoxia.