ALBERT

Description: Klimawandel im Ozean – sind Ozeanerwärmung und -versauerung ein böses Zwillingspaar? Seit der industriellen Revolution ist die Konzentration des Treibhausgases CO2 in der Atmosphäre um fast 50% gestiegen. Die Folgen sind bereits spürbar – im langsamen Anstieg der globalen Durchschnittstemperatur. Die Weltozeane mildern den Temperaturanstieg, indem sie die Effekte des Klimawandels abpuffern, doch ganz verhindern können sie ihn nicht. Im Gegenteil, auch sie werden dadurch wärmer und ihre oberen Wasserschichten versauern durch die Aufnahme von CO2. Was dies für die wechselwarmen Bewohner der Ozeane, Fische und Wirbellose, bedeutet, und welche Rolle die Wissenschaft in der internationalen Umweltpolitik spielt – darüber berichte ich Ihnen gerne auf der Open BTU.

Description: Since sensory system allows organisms to perceive and interact with their external environment, any disruption in their functioning may have detrimental consequences on their survival. Ocean acidification has been shown to potentially impair olfactory system in fish and it is therefore essential to develop biological tools contributing to better characterize such effects. The olfactory marker protein (omp) gene is involved in the maturation and the activity of olfactory sensory neurons in vertebrates. In teleosts, two omp genes (ompa and ompb) originating from whole genome duplication have been identified. In this study, bioinformatic analysis allowed characterization of the ompa and ompb genes from the European seabass (Dicentrarchus labrax) genome. The European seabass ompa and ompb genes differ in deduced amino acid sequences and in their expression pattern throughout the tissues. While both ompa and ompb mRNA are strongly expressed in the olfactory epithelium, ompb expression was further observable in different brain areas while ompa expression was also detected in the eyes and in other peripheral tissues. Expression levels of ompa and ompb mRNA were investigated in adult seabass (4 years-old, F0) and in their offspring (F1) exposed to pH of 8 (control) or 7.6 (ocean acidification, OA). Under OA ompb mRNA was down-regulated while ompa mRNA was up-regulated in the olfactory epithelium of F0 adults, suggesting a long-term intragenerational OA-induced regulation of the olfactory sensory system. A shift in the expression profiles of both ompa and ompb mRNA was observed at early larval stages in F1 under OA, suggesting a disruption in the developmental process. Contrary to the F0, the expression of ompa and ompb mRNA was not anymore significantly regulated under OA in the olfactory epithelium of juvenile F1 fish. This work provides evidence for long-term impact of OA on sensorial system of European seabass as well as potential intergenerational acclimation of omp genes expression to OA in European seabass.

Description: Global warming has already caused various environmental changes, including a loss of almost 50% Arctic sea-ice coverage since the 1980s. Sea-ice loss strengthens summer stratification and, consequently, hypoxic zones in the deep-water layers may form. The deep fjord systems of the Svalbard archipelago are particularly at risk from this long-lasting stratification. Thus, the present study aims to investigate the hypoxia tolerance of the Arctic keystone species Polar cod, Boreogadus saida. We measured the respiratory capacity (standard, routine and maximum metabolic rates, SMR, RMR, MMR) and swimming performance under progressive hypoxia (100% to 5% air saturation) at cold habitat temperatures (2.5 °C) and after warm-acclimation to close to its thermal limit (10 °C) via flow-through and swim-tunnel respirometry. The observed metabolic patterns were consistent at both acclimation temperatures: Over its full SMR and partly also MMR ranges, Polar cod displayed oxyregulating behaviour under progressive hypoxia, with SMR never below aerobic baseline metabolism. Despite the common paradigm that polar organisms are not hypoxia tolerant, Polar cod could handle very low oxygen saturations down to a Pcrit of 5.9 % air saturation at 2.5 °C. At 10°C, Pcrit rose to 21.6% air saturation. However, we did not observe any metabolic downregulation and no anaerobic component of the hypoxia response in Polar cod, usually mentioned in the definition of hypoxia tolerance. Therefore, we describe the observed response rather as metabolic hypoxia compensation than hypoxia tolerance as the mechanisms involved here actively seek to improve oxygen supply instead of (anaerobically) tolerating hypoxia through metabolic depression.

Description: The Arctic marine ecosystem is changing fast due to climate change, emphasizing the need for solid ecological baselines and monitoring. The polar cod Boreogadus saida functions as key species in the Arctic marine food web. We investigated the stomach content of polar cod from the northern Barents Sea using DNA metabarcoding with the mitochondrial cytochrome c oxidase I (COI) gene in parallel with classical visual analysis. Arctic amphipods and krill dominated the diet in both methods. Yet, metabarcoding allowed for the identification of digested and unidentifiable prey and provided higher taxonomic resolution, revealing new and undiscovered prey items of polar cod in the area. Furthermore, molecular results suggest a higher importance of barnacles and fish (supposedly eggs and pelagic larvae) in the diet than previously recorded. Parasites and, in 6 cases other prey items, were only visually identified, demonstrating the complementary nature of both approaches. The presence of temperate and boreal prey species such as Northern krill and (early life stages of) European flounder and European plaice illustrate the advection of boreal taxa into the polar region or may be indicative of ongoing borealization in the Barents Sea. We show that a combination of visual analysis and metabarcoding provides complementary and semi-quantitative dietary information, and integrative insights to monitor changing marine food webs.

Description: Antarctic fish of the suborder Notothenioidei display remarkable metabolic adaptations to life in the Southern Ocean. These comprise very low, energy saving metabolic rates, higher mitochondrial densities, cold adapted enzymes, anti-freeze proteins and last but not least, the loss of hemoglobin in the icefishes (family Channichthyidae). Yet, those adaptations come at a premium and render Antarctic notothenioids especially vulnerable to a warming ocean. As the central players in aerobic energy metabolism, mitochondria and their acclimatory plasticity play an important role in buffering the effects of climate change and much depends on their thermal stability and acclimatory capacity. I will present an overview of recent studies on notothenioid mitochondrial and whole animal respiration under acute and chronic thermal exposure and explore the differences in thermal reaction norms, leak rates and thermal stability of the individual respiratory complexes in Antarctic nototheniids (N. rossii, N. coriiceps), trematomids (T. eulepidotus, T. loennbergii) and the haemoglobin-less channichthyids (C. hamatus, C. wilsoni).

Description: Over the last three decades, an increasing interest in how climate change will affect life on earth has motivated many comparative physiologists to focus their research on the effects of Anthropogenic drivers (mainly represented by climate change and pollution) on the physiological performance of their study organisms in order to identify critical thresholds and tipping points for their sustainable existence or mere survival. Experimental work started with short term single driver experiments but soon developed to include multiple drivers and sometimes even successive generations in an attempt to address as much of climate change’s complexity as possible and include adaptive, trans-generational aspects to project physiological reaction norms into the future. Addressing those ‘big questions’ of high societal relevance have the merit of creating high visibility and also funding opportunities, however, classic comparative physiology and biochemistry is running the risk of becoming marginalized in this process, if the underlying physiological and biochemical processes cannot be visualized accordingly. In my talk, I will present recent examples of how integrative ecophysiology research can be used to inform society and policy, which potential pitfalls we, as a community of researchers in comparative physiology and biochemistry, should avoid and what challenges we are facing when trying to balance fundamental research with answering the ‘big questions’.

Description: Antarctic fish of the suborder Notothenioidei display remarkable metabolic adaptations to life in the Southern Ocean. These comprise very low, energy saving metabolic rates, higher mitochondrial densities, cold adapted enzymes, anti-freeze proteins and last but not least, the loss of hemoglobin in the icefishes (family Channichthyidae). Yet, those adaptations come at a premium and render Antarctic notothenioids especially vulnerable to a warming ocean. As the central players in aerobic energy metabolism, mitochondria and their acclimatory plasticity play an important role in buffering the effects of climate change and much depends on their thermal stability and acclimatory capacity. I will present an overview of my studies on notothenioid mitochondria under acute and chronic thermal exposure and explore the differences in thermal reaction norms, leak rates and thermal stability of the individual respiratory complexes in Antarctic nototheniids (N. rossii, N. coriiceps), trematomids (T. eulepidotus, T. loennbergii) and channichthyids (C. hamatus, C. wilsoni) and contrast them to Austral nototheniids (N. angustata) as well as Arctic and temperate gadoids.

Description: In this study, we adapted Star-Oddi micro-HRT (G2) bio-loggers for improved function in the cold-adapted Arctic key species Polar cod (B. saida) that generally displays a very low heart rate (ƒH) of 8bpm. To integrate ƒH data with oxygen consumption rates (MO2), we conducted critical swim speed (Ucrit) tests in a swim-tunnel respirometer within the ecologically relevant temperature range of 0–8°C. A significant correlation (p 〈 0.01) of observed cardiorespiratory parameters indicated primary dependency of ƒH and MO2 during acute warming, suggesting a species-specific potential of ƒH as a proxy for energy expenditure. Despite present Ucrit (2.3 ± 0.3 BL/s) being 20% lower than in untagged conspecifics at similar temperature, maximum metabolic rates were 35% higher for bio-logger-bearing individuals. Apparent excess potential to increase MO2 suggests that polar cod’s performance limitations are not dictated by the absolute capacity of oxygen supply. Hence, alternative explanations determining Ucrit, such as behavioral termination of swimming trials to save energy, or potential limitations in ATP supply to the muscle, are discussed. Heart rate was significantly impacted by both temperature and swimming velocity (p 〈 0.0001, respectively). Past the optimal temperature range of polar cod (2.8–4.4°C), heart rate ceased to increase, with incremental Q10 values levelling off from 2.63±0.43 at 0–2°C, to 1.73±0.74 at 6–8°C. Consequently, potential impacts of insufficient heart rate scaling with acute temperature rise are discussed in the light of projected Arctic warming.