ALBERT

Description: The present study investigated the response of an Arctic keystone species, Polar cod, Boreogadus saida, to hypoxia and warming. We measured the respiratory capacity (standard, routine and maximum metabolic rates, SMR, RMR, MMR, aerobic scope, critical oxygen saturation (Pcrit)) and swimming performance of Polar cod under progressive hypoxia at 2.4 °C and after warm acclimation to close to the species' thermal limit (10.0 °C) via intermittent-flow and swim tunnel respirometry. Polar cod for the experiments in this study were caught in October 2018 during RV HEINCKE expedition HE519 in Billefjorden (78°34'59.99 N 16°27'59.99 E). In total 46 fish were selected for this experiment and divided into two groups. The first group (n = 30, group C) measured 19.7 ± 1.3 cm and 39.6 ± 9.5 g and was kept at habitat temperatures. The second group (n=16, group WA) with an average size of 19.8 ±1.9 cm and weight of 41.3 ± 10.1 g, was progressively acclimated to 10.0 °C (warming rate: 1.5 °C month-1) and then kept at this temperature for several months. For both temperatures, SMR and RMR were measured using seven fully automated respiration chambers (Loligo Systems ApS, Denmark), submerged in two connected thermoregulated tanks (170 L). Oxygen consumption was measured in 12 different PO2 conditions, 100, 75, 65, 55, 45, 35, 30, 25, 20, 15, 10 and 5% air saturation (n = 7 per conditions). Each oxygen saturation was maintained for two days and two nights, containing approximately 80-100 measurement phases during which fish were left undisturbed to ensure proper determination of the SMR as they habituated to the experimental conditions. Only the metabolic rate data from the second night were used for SMR calculation. The respirometers' measurement cycles were 5 min flush, and 30.5 min measurement in the cold group (C) and 2.5 min flush, and 17.5 min measurement in the WA group. The metabolic rate and swimming performance of B. saida under hypoxia were recorded following a critical swimming speed (Ucrit) protocol (Brett (1964), modified after Kunz et al. (2018)) applying the same PO2 steps as in the respiration chambers (100, 75, 65, 55, 45, 35, 30, 25, 20, 15 and 10 % air saturation). A Brett-type swim tunnel respirometer of 5 L (test section 28 x 7.5 x 7.5 cm, Loligo Systems ApS, Denmark) was used to measure the swimming performance of B. saida (n=6-7 per PO2 treatment). The fish were transferred to the swim tunnel, seven days (C) or three (WA) days after the last feeding. After an acclimatisation period of 1.5 h in stagnant water, water velocity was increased to 1.2 BL (body length)/sec for 25 min. Afterwards, the velocity was increased to the first measurement velocity of 1.4 BL/sec before starting the Ucrit protocol. Each velocity step contained an ṀO2 measurement cycle, comprising a 60 s flush phase followed by 120 s of stabilisation and an 8 min measuring period, after which water velocity was increased by 0.15 BL/sec. Each measurement period thus returned 480 single oxygen recordings from which oxygen consumption (ṀO2) was calculated. The swim chamber was covered to minimise disturbance. The step-wise water velocity increase was performed until exhaustion, when the fish completely refused to swim and remained inactive for more than three minutes. The maximum metabolic rate was determined for each PO2 level inside the swim tunnel. To determine the gait‐transition speed Ugait (the switch from strictly aerobic to anaerobically supplemented swimming) (Drucker and Jensen, 1996), kick-and-glide swimming (so called "bursts") (Videler, 1981) was documented. In kick-and-glide swimming, thrust generation is supplemented by anaerobic muscle contractions and mainly white muscle is used. All bursts were counted and the corresponding time during the swim trial was documented. The critical swimming velocities (Ucrit) of the fish were calculated according to Brett (1964). After Ucrit was reached, the velocity was immediately decreased to the basic weaning velocity of 1.4 BL/sec and the fish stayed in the swim tunnel for another 10 min before being transferred back into their tanks. Blank respiration in the swim tunnel accounted for less than 2% ṀO2. The swim tunnel was cleaned daily.

Description: Marine organisms and entire ecosystems are influenced by increasing temperatures and increasing CO2 partial pressure (hypercapnia). The experimental organism of this thesis, the marine teleost Gadus morhua, inhabits regions that are supposed to experience some of the largest climatic changes on the globe. The aim of this study was to investigate the effects of ocean acidification and increasing temperature on the physiological mechanisms in the heart of Gadus morhua in order to draw conclusions for the whole organism. The fish were divided into two groups, one was incubated under ambient pCO2 (390 μatm) and the other group under future pCO2 levels (1170 μatm; scenario after IPCC: RCP 8.5). Both groups were split into four different temperature levels (3, 8, 12 and 16 °C) with 12 animals in each treatment. The main focus was on the metabolic products of glycolysis, citric acid cycle, lactic acid cycle, amino acid metabolism and amino acid derivatives. Results show that environmental hypercapnia led to a significant decrease of glucose-6- phosphate (glycolysis), on amino acids and their derivatives alanine, glutamine,isoleucine, creatine phosphate, glucarate and taurine. The elevation of temperature led to a significant increase of creatine (amino acid derivatives) and lactate in the treatment groups with 390 μatm CO2. Hypercapnic accumulation did not significantly influence the metabolites of the citric acid cycle. Furthermore, similar ATP concentrations through all treatments indicated that Gadus morhua is able to cope with environmental changes and to maintain its supply of energy.

Description: Since the beginning of the industrialization, uncontrolled greenhouse gas emission led to a distinct temperature increase on earth. Arctic environments are projected to experience the most severe changes due to climate change. Higher atmospheric temperatures caused already various environmental changes, for example a decrease in Arctic sea ice of 49 % (1979-2000) and increasing carbon dioxide concentrations which reduced the sea surface pH. A reduced sea ice formation will strengthen the summer stratification of warm, oxygen poor on top of cold, oxygen rich water masses, which may consequently cause local hypoxia in ground water layers. As a result, the deep cold water layers do not receive oxygen-rich water and oxygen consumption extends over more than one season. This can lead to local hypoxia in the ground water layers of the protected fjords. Especially endangered of this long-lasting stratification in winter are the deep fjord systems of the Svalbard archipelago. In this region, the change of winter temperatures from 1961–90 corresponded to an increase of 0.6 °C per decade. Corresponding, an additional increase of 0.9 °C per decade is projected for 2071–2100. Thus, the present study investigates the hypoxia tolerance of Polar cod, Boreogadus saida, one of the main Arctic key species. Therefore, different performance parameters were determined. The respiratory capacity as well as the swimming performance under declining oxygen concentrations were measured in two different experimental setups. A sample size of 30 Polar cod with similar body length and weight were chosen. All individuals were used several times during the experiments. First, the routine (RMR) and standard metabolic rate (SMR) were determined via flow-through respirometry. The calculated SMR for Polar cod accounted 0.44 μmol O2/g∙h. The RMR followed an oxygen regulating pattern, indicating that aerobic metabolic pathways such as lipid oxidation were used, rather than anaerobic pathways. This implies a relatively small contribution of anaerobic metabolism to the energy production in B. saida. This was confirmed in the swim tunnel experiments. However, Ugait (the speed at which the fish changed to anaerobically fuelled swimming) was not significantly affected by hypoxia, the total number of bursts (p = 0.025) and total active swimming time (p = 0.017) significantly decreased with decreasing oxygen saturation. The loss of anaerobic swimming capacity due to hypoxia may endanger this species in regard to predator-prey-interactions and loss of escape reactions. Under exercise Polar cod was able to up-regulate its maximum metabolic rate (MMR) until a threshold of 45 % PO2 was reached. Afterwards, the oxygen consumption significantly decreased with decreasing oxygen concentrations. Throughout both experiments neither RMR nor MMR decreased below SMR level. Furthermore, the present study revealed that Polar cod is an extremely hypoxia tolerant fish species, which is able to handle oxygen saturations down to a Pcrit of 4.81 % PO2. This outstanding capability could give the otherwise rather disadvantaged fish species an advantage under changing climate conditions.

Description: Since the beginning of the industrialization, uncontrolled greenhouse gas emission led to a distinct temperature increase on earth. Arctic environments are projected to experience the most severe changes due to climate change. Higher atmospheric temperatures caused already various environmental changes, for example a decrease in Arctic sea ice of 49 % (1979-2000) and increasing carbon dioxide concentrations which reduced the sea surface pH. A reduced sea ice formation will strengthen the summer stratification of warm, oxygen poor on top of cold, oxygen rich water masses, which may consequently cause local hypoxia in ground water layers. As a result, the deep cold water layers do not receive oxygen-rich water and oxygen consumption extends over more than one season. This can lead to local hypoxia in the ground water layers of the protected fjords. Especially endangered of this long-lasting stratification in winter are the deep fjord systems of the Svalbard archipelago. In this region, the change of winter temperatures from 1961–90 corresponded to an increase of 0.6 °C per decade. Corresponding, an additional increase of 0.9 °C per decade is projected for 2071–2100. Thus, the present study investigates the hypoxia tolerance of Polar cod, Boreogadus saida, one of the main Arctic key species. Therefore, different performance parameters were determined. The respiratory capacity as well as the swimming performance under declining oxygen concentrations were measured in two different experimental setups. A sample size of 30 Polar cod with similar body length and weight were chosen. All individuals were used several times during the experiments. First, the routine (RMR) and standard metabolic rate (SMR) were determined via flow-through respirometry. The calculated SMR for Polar cod accounted 0.44 μmol O2/g∙h. The RMR followed an oxygen regulating pattern, indicating that aerobic metabolic pathways such as lipid oxidation were used, rather than anaerobic pathways. This implies a relatively small contribution of anaerobic metabolism to the energy production in B. saida. This was confirmed in the swim tunnel experiments. However, Ugait (the speed at which the fish changed to anaerobically fuelled swimming) was not significantly affected by hypoxia, the total number of bursts (p = 0.025) and total active swimming time (p = 0.017) significantly decreased with decreasing oxygen saturation. The loss of anaerobic swimming capacity due to hypoxia may endanger this species in regard to predator-prey-interactions and loss of escape reactions. Under exercise Polar cod was able to up-regulate its maximum metabolic rate (MMR) until a threshold of 45 % PO2 was reached. Afterwards, the oxygen consumption significantly decreased with decreasing oxygen concentrations. Throughout both experiments neither RMR nor MMR decreased below SMR level. Furthermore, the present study revealed that Polar cod is an extremely hypoxia tolerant fish species, which is able to handle oxygen saturations down to a Pcrit of 4.81 % PO2. This outstanding capability could give the otherwise rather disadvantaged fish species an advantage under changing climate conditions.

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.