Hypoxia Toleranz der Riesen-Flugkalmare (Dosidicusgigas) in den Sauerstoffminimumzonen des östlichenPazifiks: Physiologische und biochemische Mechanismen

Marine hypoxia has become one of the major concerns of the world, as oceanic dead zones continue expanding horizontally and vertically, a phenomenon primarily caused by global warming and anthropogenic eutrophication. As consequence, drastic changes in community structures, predator-prey relationships (i.e. uncoupling) and/or habitat compression are expected followed by severe impacts on food-webs, ecosystems and fisheries. Moreover, habitat compression is aggravated by the synergistic effects of climate change, as elevated temperature and PCO2 will narrow the habitat from above. The jumbo squid, Dosidicus gigas, undergoes diel vertical migrations into oxygen minimum zones (OMZs) off the Eastern Tropical Pacific, where he plays an important ecological role both as predator and prey. In fact, this species can easily remove more than 4 million tons of food per year from the pelagic food web and is an important component in the diets of birds, fishes, and mammals. Besides its ecological role, the jumbo squid also plays an important economically role being target of the world’s largest cephalopod fishing industry with around 14% of world’s total squid catch and landings estimated at 818,000 tons in 2006. However, the main problem that arises with hypoxia is a reduced gradient that drives O2 uptake via diffusion pathways. At some point, the critical O2 partial pressure (Pcrit), the reduced diffusion gradient cannot support the metabolic demand fully aerobically, and has to be supplemented by anaerobic pathways and/or compensated by a reduction in metabolic rate. Commonly, aquatic animals respond to hypoxia by first attempting to maintain O2 delivery, as aerobic metabolism is much more efficient, followed by conserving energy expenditure and reducing energy turn over and finally by enhancing energetic efficiency of those metabolic processes that remain and derive energy from anaerobic sources. A further problem that vertical migrators of OMZs have to face is the elevated production of radical oxygen species (ROS) during the reoxygenation phase while ascending, as non-neutralized ROS formation can damage biological macromolecules (i.e. lipids, proteins and DNA) resulting in severe functional alterations in cells and tissues. To determine the cost and benefits of such diel vertical migrations, I investigated biochemical and physiological mechanisms in juvenile D. gigas off the Gulf of California with a focus on ventilation, locomotion, metabolism and antioxidant defense. The respiratory regulation in D. gigas was unpredictably high and is mirrored in maximized oxygen extraction efficiencies (EO2) at early (EH, < 160 min, 1 kPa O2) and late hypoxia (LH, > 180 min, 1 kPa O2). EO2 at EH was maximum 82% and achieved via (1) deep-breathing mechanism with more powerful contractions and an enlarged inflation period, and (2) reduction in the relaxed mantle diameter to favor diffusion. At LH, EO2 was still 40%, despite all other ventilatory mechanisms were drastically reduced, probably by using the collar-flap system (uncoupling of locomotory and ventilatory mechanisms) and a further reduction in the relaxed mantle diameter. Moreover, the drastic change in locomotion between EH and LH (onset of lethargy) was accompanied by a switch in the energy source of anaerobic pathways. At EH, anaerobic energy equivalents (AEE) primarily arrived via rapid energy reserve depletion (ATP, phospho-L-arginine), and, under LH, was mainly obtained via fermentative pathways (mainly octopine). As octopine formation simultaneously creates protons, intracellular acidosis and acid-base disturbances under progressing hypoxia are expected, which might negatively impact squid’s energy household and expenditures from locomotion towards more important cellular processes (i.e. ion regulation). Energy reserve depletion might even trigger lethargic behavior to conserve energy and extend hypoxia residence time. At EH, in contrast, deep-breathing behavior enabled D. gigas to pass the same amount of water through the mantle cavity per period of time and thereby could maintain a stable ventilatory volume per min, which explains its high level of activity observed under such extreme conditions. Moreover, D. gigas suppressed its metabolism (45-60%) at severe hypoxia (below Pcrit), as the reduction in O2 consumption rate (70-80%) could not be compensated by an upregulation in anaerobic energy production (70%). Cephalopods primarily feed on proteins and their glycogen storage potential is low (< 0.4% of body weight). Therefore anaerobic protein degradation came into focus as strategy in hypoxia tolerant species. Yet, total protein concentration in muscle tissue of D. gigas did not vary significantly under severe hypoxia, but the reduced protein expression of heat shock protein 90 (Hsp90) and α- actinin indicates that, at least under progressing hypoxia, jumbo squids might degrade specific muscle proteins anaerobically. Moreover, the lower α-actinin expression at LH might be related to a decreased protection via the Hsp90 chaperon machinery resulting in increased ubiquitination and subsequent degradation. Therefore, the ubiquitin-proteasome system seems to play an important role in hypoxia tolerance, but further investigations are necessary to discover its full potential and pathways. Antioxidant enzyme activities in D. gigas were generally low and in the range of other squid species, but malondialdehyde concentrations (indicative of cellular damage) did not significantly change between normoxic and hypoxic conditions, demonstrating an efficient antioxidant defense system. Moreover, superoxide dismutase and catalase activities were enhanced under normoxia that seem to constitute an integrated stress response at shallower depths by buffering increased ROS formation, and, in addition, might even be a strategy to cope with the reoxygenation/recovery process. Moreover, heat shock protein 70 concentration was significantly increased under severe hypoxia (1 kPa O2), which may constitute a preparation for the reoxygenation phase during squid’s upward migration. Accordingly, the present thesis demonstrates that D. gigas evolved a variety of adaptive mechanisms and strategies to cope with hypoxia and the imposed challenges of diel vertical migrations. D. gigas might even actively descent into OMZs to suppress metabolism and escape from high metabolic demands at surface waters. Especially the high O2 uptake capacity and respiratory regulation were surprising taking into account cephalopods physiological and anatomical restraints. Therefore, D. gigas seems well-adapted to hypoxic conditions and might even out-compete less hypoxia tolerant species under hypoxia expansion, but the synergistic impacts of climate change, in turn, might endanger its survival.Die vertikale und horizontale Ausbreitung mariner Hypoxie hat sich zu einem der grössten Umweltprobleme der Welt entwickelt, ein Phänomen, dass hauptsächlich durch die globale Erwärmung und anthropogene Eutrophierung verursacht wird. Als Konsequenz sind drastische Veränderungen in der Zusammensetzung und dem Aufbau mariner Tier- und Pflanzengemeinschaften, sowie Änderungen in Räuber-Beute Beziehungenen (z.B. durch Entkopplung) und/oder eine Komprimierung der Lebensräume zu erwarten, was erhebliche Einflüsse auf die Nahrungsnetze, Ökosysteme und Fischerei zur Folge haben wird. Zudem wird die Komprimierung der Habitate durch die synergistischen Effekte der Klimaveränderung verschärft, da erhöhte Temperaturen und PCO2-Werte die Lebensräume zusätzlich von oben her einengen. Der Riesen-Flugkalmar, Dosidicus gigas, unternimmt tägliche Vertikalwanderungen in die Sauerstoffminimumzonen (OMZs) des östlichen tropischen Pazifiks, wo er eine wichtige ökologische Rolle als Räuber und Beute spielt. Tatsächlich kann diese Art mit Leichtigkeit mehr als 4 Millionen Tonnen Nahrung pro Jahr aus dem pelagischen Nahrungsnetz entfernen und ist ein wichtiger Bestandteil auf dem Speiseplan von Vögeln, Fischen und Säugetieren. Neben seiner ökologischen Stellung nimmt der Riesen-Flugkalmar auch eine bedeutende wirtschaftliche Rolle ein, da er eine der begehrtesten Zielscheiben der Fischereiindustrie für Kopffüssler ist und dabei alleine 14% des gesamten weltweiten Tintenfischfangs abdeckt mit geschätzten Anlandungen von 818,000 Tonnen im Jahr 2006. Das Hauptproblem der Hypoxie ist ein verringerter Gradient, der die Sauerstoffaufnahme über Diffusionswege steuert. Erreicht dieser Gradient den kritischen Sauerstoffpartialdruck (Pcrit) können die Anforderungen des Stoffwechsels nicht mehr alleine durch Atmungsprozesse abgedeckt werden, und muss daher mit Hilfe anaerober Stoffwechselwege ergänzt und/oder mit einer Reduktion des Stoffwechsels kompensiert werden. Weil der aerobe Stoffwechsel viel energiereicher ist versuchen aquatische Organismen unter Hypoxie als erstes den Sauerstofftransport aufrecht zu erhalten, gefolgt von der Konservierung von Energieausgaben, einem verringertem Energieumsatz, und letztendlich durch die Erhöhung der Energieeffizienz von Stoffwechselprozessen, welche Energie aus anaeroben Quellen beziehen und aufrechterhalten. Ein weiteres Problem, das sich Vertikalwanderer in OMZs stellen müssen, ist die erhöhte Produktion von Sauerstoffradikalen (ROS) während der Reoxygenierungsphase beim Aufsteigen, da nicht neutralisierte ROS Formierungen biologische Makromoleküle (wie z.B. Lipide, Proteine und DNA) beschädigen können, was wiederum erhebliche funktionelle Veränderungen in Zellen und Geweben hervorrufen kann. Um die Kosten und Vorteile solcher Vertikalwanderungen bestimmen zu können, habe ich ihm Rahmen meiner Doktorarbeit die biochemischen und physiologischen Mechanismen juveniler Riesen-Flugkalmare aus dem Golf von Kalifornien untersucht, und mich dabei auf die Atmung, die Bewegung, den Stoffwechsel und die Antioxidansabwehr fokussiert. Die respiratorische Regulierung in D. gigas war wiedererwartend hoch und wiedergespiegelt in einer erhöhten Sauerstoffaufnahmeeffizienz (EO2) sowohl unter früher (EH, 180 min, 1 kPa O2). Die EO2 unter EH erreichte einen maximalen Wert von 82% und wurde erzielt durch (1) einen Tief- Atmungs-Mechanismus mit kraftvolleren Mantelkontraktionen und einer verlängerten Inflationsperiode, und (2) eine Verringerung des Manteldurchmessers (im Ruhezustand) um die Sauerstoffaufnahme über Diffusion zu steigern. Unter LH, EO2 betrug weiterhin 40%, obwohl alle anderen Atmungsmechanismen drastisch reduziert waren. Dies wurde vermutlich erzielt durch die Anwendung des sogenannten Mantelkragen-Klapp-Systems (durch Entkopplung der Ventilation von den Bewegungsabläufen) und einer weiteren Reduzierung des Manteldurchmessers (im Ruhezustsand). Desweiteren, war die drastische Änderung der Lokomotion/Atmung zwichen EH und LH (Startpunkt der Lethargie) begleitet von einer Umstellung in der Energieverstoffwechslung unter anaeroben Bedingungen. Während der Grossteil der anaeroben Energieequivalente (AEE) unter EH durch den schnellen Abbau von Energiereserven (ATP, Phospho-L-Arginin) gedeckt werden konnte, wurde unter LH der Hauptanteil über Fermentationswege (hauptsächlich Oktopin) gewonnen. Die Bildung des anaeroben Endproduktes Oktopin aber erzeugt gleichzeitig Protonen, und daher sind intrazelluläre Versauerung und Störungen des Säure-Base Gleichgewichtes zu erwarten. Daher sind Störungen/Änderungen im Energiehaushalt und seinen Ausgaben zu erwarten mit einem erhöhten Fokus auf wichtige zelluläre Prozesse (wie z.B. Ionenregulation) anstelle der Lokomotion. Zusätzlich ist es möglich, dass die Ausbeutung von Energiereserven selbst lethargisches Verhalten auslöst, um Energieausgaben zu konservieren und die Aufenthaltszeit unter hypoxischen Bedingungen zu verlängern. Im Gegensatz dazu, ermöglichte das Tief-Atmungs-Verhalten von D. gigas unter EH einen konstanten Wassertransport durch die Mantelhöhle pro Zeitintervall wie unter normoxischen Bedingungen, was den hohen Aktivitätsgrad unter solchen extremen Bedingungen erklären könnte. Zusätzlich zeigte D. gigas unter Hypoxie eine aktive Absenkung seines Stoffwechsels (45- 60%), da die verringerte Atmungsrate (70-80%) nicht durch die Aktivierung anaerober Stoffwechselwege kompensiert werden konnte (AEE 70% erhöht). Kopffüssler unter normoxischen Bedingungen beziehen ihre Energie weitgehend aus Proteinen und ihr Potential Glykogen zu speichern ist äusserst begrenzt (< 0.4% des Körpergewichts). Daher könnnte der anaerobe Abbau von Proteinen eine wichtige Rolle in der Hypoxietoleranz von Kopffüsslern spielen, als weitere Strategie, um die Aufenthaltszeit in OMZs zu verlängern. Die Proteinkonzentration im Muskelgewebe von D. gigas allerdings variierte nicht signifikant unter dem Einfluss von Hypoxie (1 kPa O2), trotzdem konnte eine reduzierte Proteinexpression des Hitzeschockproteins 90 (Hsp90) und α-actinin entdeckt werden, was zumindest unter fortschreitender Hypoxie darauf schliessen lässt, dass D. gigas spezifische Muskelproteine anaerobisch verstoffwechselt. Weiterhin scheint die verringerte Expression von α-actinin unter LH mit einem reduzieten Schutz der Hsp90 Chaperon-Maschinerie zusammenzuhängen, was wiederum eine erhöhte Ubiquitinierung mit anschliessender Degradierung zur Folge hat. Dies lässt darauf schliessen, dass das Ubiquitin-Proteasom- System eine entscheidende Rolle in der Hypoxietoleranz spielt, aber weitere Untersuchungen sind notwending um das gesamte Potential und seine Pfade erfassen zu können. Die antioxidantischen Enzymaktivitäten in D. gigas zeigten generell niedrige Werte im Bereich anderer Tintenfischarten, wobei die Malondialdehydkonzentrationen (Anzeiger für Zellschäden) keine signifikanten Veränderungen zwischen Normoxie und Hypoxie aufzeigte, was wiederum einen effizienten Antioxidansabwehrmechanismus aufzeigt. Zudem waren die Enzymaktivitäten von Superoxiddismutase und Katalase unter Normoxie gesteigert, was mit einer integrierten Stressantwort im Oberflächenwasser zusammenzuhängen scheint, und möglicherweise sogar selbst eine Strategie darstellt, um mit der Reoxygenierung/ Erholungsphase umzugehen, um die erhöhte ROS Produktion abzupuffern. Die signifikante Erhöhung der Hitzeschockprotein 70 Konzentration unter Hypoxie (1 kPa O2) scheint dabei eine zusätzliche Vorsorgemassnahme bezüglich der Reoxygenierungsphase in aufsteigenden Riesen-Flugkalmaren darzustellen. Die Ergebnisse meiner Doktorarbeit zeigen, dass D. gigas eine Vielzahl von adaptiven Mechansimen und Strategien entwickelt hat, welche ihm ermöglichen mit hypoxischen Bedingungen und den Herausforderungen der Vertikalwanderungen umzugehen. D. gigas sucht dabei möglicherweise absichtlich OMZs auf, um seinen hohen Energieverbrauch aktiv zu unterdrücken, um vor seinen hohen Stoffwechselanforderungen im Oberflächenwasser zu flüchten. Besonders die erhöhte Sauerstoffaufnahmeeffizienz und respiratorische Regulation waren überraschend, vor allem unter dem Aspekt der physiologischen und anatomischen Beinträchtigungen die Kopffüssler typischerweise charakterisieren. Daher scheint D. gigas sehr gut an hypoxische Bedingungen angepasst zu sein und kann vermutlich bei weiterer Hypoxieausbreitung weniger tolerante Arten verdrängen. Trotzalledem könnten die synergistischen Einflüsse des Klimawandels das Überleben von D. gigas drastisch beinträchtigen

Hypoxia tolerance of jumbo squids (Dosidicus gigas) in the Eastern Pacific oxygen minimum zones: Physiological and biochemical mechanisms

Marine hypoxia has become one of the major concerns of the world, as oceanic dead zones continue expanding horizontally and vertically, a phenomenon primarily caused by global warming and anthropogenic eutrophication. As consequence, drastic changes in community structures, predator-prey relationships (i.e. uncoupling) and/or habitat compression are expected followed by severe impacts on food-webs, ecosystems and fisheries. Moreover, habitat compression is aggravated by the synergistic effects of climate change, as elevated temperature and PCO2 will narrow the habitat from above. The jumbo squid, Dosidicus gigas, undergoes diel vertical migrations into oxygen minimum zones (OMZs) off the Eastern Tropical Pacific, where he plays an important ecological role both as predator and prey. In fact, this species can easily remove more than 4 million tons of food per year from the pelagic food web and is an important component in the diets of birds, fishes, and mammals. Besides its ecological role, the jumbo squid also plays an important economically role being target of the world’s largest cephalopod fishing industry with around 14% of world’s total squid catch and landings estimated at 818,000 tons in 2006. However, the main problem that arises with hypoxia is a reduced gradient that drives O2 uptake via diffusion pathways. At some point, the critical O2 partial pressure (Pcrit), the reduced diffusion gradient cannot support the metabolic demand fully aerobically, and has to be supplemented by anaerobic pathways and/or compensated by a reduction in metabolic rate. Commonly, aquatic animals respond to hypoxia by first attempting to maintain O2 delivery, as aerobic metabolism is much more efficient, followed by conserving energy expenditure and reducing energy turn over and finally by enhancing energetic efficiency of those metabolic processes that remain and derive energy from anaerobic sources. A further problem that vertical migrators of OMZs have to face is the elevated production of radical oxygen species (ROS) during the reoxygenation phase while ascending, as non-neutralized ROS formation can damage biological macromolecules (i.e. lipids, proteins and DNA) resulting in severe functional alterations in cells and tissues. To determine the cost and benefits of such diel vertical migrations, I investigated biochemical and physiological mechanisms in juvenile D. gigas off the Gulf of California with a focus on ventilation, locomotion, metabolism and antioxidant defense. The respiratory regulation in D. gigas was unpredictably high and is mirrored in maximized oxygen extraction efficiencies (EO2) at early (EH, 180 min, 1 kPa O2). EO2 at EH was maximum 82% and achieved via (1) deep-breathing mechanism with more powerful contractions and an enlarged inflation period, and (2) reduction in the relaxed mantle diameter to favor diffusion. At LH, EO2 was still 40%, despite all other ventilatory mechanisms were drastically reduced, probably by using the collar-flap system (uncoupling of locomotory and ventilatory mechanisms) and a further reduction in the relaxed mantle diameter. Moreover, the drastic change in locomotion between EH and LH (onset of lethargy) was accompanied by a switch in the energy source of anaerobic pathways. At EH, anaerobic energy equivalents (AEE) primarily arrived via rapid energy reserve depletion (ATP, phospho-L-arginine), and, under LH, was mainly obtained via fermentative pathways (mainly octopine). As octopine formation simultaneously creates protons, intracellular acidosis and acid-base disturbances under progressing hypoxia are expected, which might negatively impact squid’s energy household and expenditures from locomotion towards more important cellular processes (i.e. ion regulation). Energy reserve depletion might even trigger lethargic behavior to conserve energy and extend hypoxia residence time. At EH, in contrast, deep-breathing behavior enabled D. gigas to pass the same amount of water through the mantle cavity per period of time and thereby could maintain a stable ventilatory volume per min, which explains its high level of activity observed under such extreme conditions. Moreover, D. gigas suppressed its metabolism (45-60%) at severe hypoxia (below Pcrit), as the reduction in O2 consumption rate (70-80%) could not be compensated by an upregulation in anaerobic energy production (70%). Cephalopods primarily feed on proteins and their glycogen storage potential is low (< 0.4% of body weight). Therefore anaerobic protein degradation came into focus as strategy in hypoxia tolerant species. Yet, total protein concentration in muscle tissue of D. gigas did not vary significantly under severe hypoxia, but the reduced protein expression of heat shock protein 90 (Hsp90) and α- actinin indicates that, at least under progressing hypoxia, jumbo squids might degrade specific muscle proteins anaerobically. Moreover, the lower α-actinin expression at LH might be related to a decreased protection via the Hsp90 chaperon machinery resulting in increased ubiquitination and subsequent degradation. Therefore, the ubiquitin-proteasome system seems to play an important role in hypoxia tolerance, but further investigations are necessary to discover its full potential and pathways. Antioxidant enzyme activities in D. gigas were generally low and in the range of other squid species, but malondialdehyde concentrations (indicative of cellular damage) did not significantly change between normoxic and hypoxic conditions, demonstrating an efficient antioxidant defense system. Moreover, superoxide dismutase and catalase activities were enhanced under normoxia that seem to constitute an integrated stress response at shallower depths by buffering increased ROS formation, and, in addition, might even be a strategy to cope with the reoxygenation/recovery process. Moreover, heat shock protein 70 concentration was significantly increased under severe hypoxia (1 kPa O2), which may constitute a preparation for the reoxygenation phase during squid’s upward migration. Accordingly, the present thesis demonstrates that D. gigas evolved a variety of adaptive mechanisms and strategies to cope with hypoxia and the imposed challenges of diel vertical migrations. D. gigas might even actively descent into OMZs to suppress metabolism and escape from high metabolic demands at surface waters. Especially the high O2 uptake capacity and respiratory regulation were surprising taking into account cephalopods physiological and anatomical restraints. Therefore, D. gigas seems well-adapted to hypoxic conditions and might even out-compete less hypoxia tolerant species under hypoxia expansion, but the synergistic impacts of climate change, in turn, might endanger its survival

Calcifying invertebrates succeed in a naturally CO2 enriched coastal habitat but are threatened by high levels of future acidification

CO2 emissions are leading to an acidification of the oceans. Predicting marine community vulnerability towards acidification is difficult, as adaptation processes cannot be accounted for in most experimental studies. Naturally CO2 enriched sites thus can serve as valuable proxies for future changes in community structure. Here we describe a natural analogue site in the Western Baltic Sea. Seawater pCO2 in Kiel Fjord is elevated for large parts of the year due to upwelling of CO2 rich waters. Peak pCO2 values of >230 Pa (>2300 μatm) and pHNBS values of 400 Pa (>4000 μatm). These changes will most likely affect calcification and recruitment, and increase external shell dissolution

Food Supply and Seawater pCO2 Impact Calcification and Internal Shell Dissolution in the Blue Mussel Mytilus edulis

Progressive ocean acidification due to anthropogenic CO2 emissions will alter marine ecosytem processes. Calcifying organisms might be particularly vulnerable to these alterations in the speciation of the marine carbonate system. While previous research efforts have mainly focused on external dissolution of shells in seawater under saturated with respect to calcium carbonate, the internal shell interface might be more vulnerable to acidification. In the case of the blue mussel Mytilus edulis, high body fluid pCO2 causes low pH and low carbonate concentrations in the extrapallial fluid, which is in direct contact with the inner shell surface. In order to test whether elevated seawater pCO2 impacts calcification and inner shell surface integrity we exposed Baltic M. edulis to four different seawater pCO2 (39, 142, 240, 405 Pa) and two food algae (310–350 cells mL−1 vs. 1600–2000 cells mL−1) concentrations for a period of seven weeks during winter (5°C). We found that low food algae concentrations and high pCO2 values each significantly decreased shell length growth. Internal shell surface corrosion of nacreous ( = aragonite) layers was documented via stereomicroscopy and SEM at the two highest pCO2 treatments in the high food group, while it was found in all treatments in the low food group. Both factors, food and pCO2, significantly influenced the magnitude of inner shell surface dissolution. Our findings illustrate for the first time that integrity of inner shell surfaces is tightly coupled to the animals' energy budget under conditions of CO2 stress. It is likely that under food limited conditions, energy is allocated to more vital processes (e.g. somatic mass maintenance) instead of shell conservation. It is evident from our results that mussels exert significant biological control over the structural integrity of their inner shell surfaces

Effects of ocean acidification on key physiological parameters in the green sea urchin Strongylocentrotus droebachiensis

Since the last two centuries anthropogenic C02 emissions arising from the combustion of fossil fuels have altered seawater chemistry far more rapidly than previously experienced in earth history. The rate and extent of this change are expected to affect marine organisms and entire ecosystems. Excess C0 2 diffuses from the atmosphere into ocean surface waters, resulting in elevated seawater C02 partial pressure, as weil as reduced [CO3 2-] and pH. These changes in carbonate system speciation have been demonstrated to especially impact calcifying organisms. The present study focuses on the effects of ocean acidification on adult specimens of the green sea urchin Strongylocentrotus droebachiensis, a keystone predator and grazer in ecosystems of the northern hemisphere. Laboratory experiments revealed that the potential of S. droebachiensis to cope with COrdriven ocean acidification is surprisingly high. The green sea urchin was able to fully compensate its extracellular pH by active accumulation of HC03- ions (3-4 mM) under exposure to 140 Pa. Thereby, accumulation of HC03- was facilitated by active ion regulation processes and not due to passive shell dissolution. Between the pC02 treatments 140 and 400 Pa, an ion exchange capacity limit was detected, beyond this the extracellular pH could no langer be achieved and declined by about 0.2 units. Simultaneously, in high pC02 treatments (400 Pa), extracellular bicarbonate concentration was maintained, resulting in a partial compensation of S. droebachiensis extracellular body fluid. Under long-term exposure ( 400 Pa), an upregulation of respiratory chain cytochrome oxidase in the podia of the green sea urchin could point at mitochondrial proliferation and a general elevation in aerobic metabolism, as active compensation of extracellular pH increases total energy demand. The suggested metabolic upregulation could potentially ameliorate some of the effects of increased acidity, but at similar feeding intake rates it might come at a substantial cost (e.g. decreased reproduction, slower growth) if sustained in the long-term. However, the unexpected high capacity to compensate near-future ocean acidification could be linked to an adaptation to the environmental stressor hypoxia, occurring periodically in the Western Baltic. Previous work on the biological consequences of COrdriven ocean acidification has suggested that calcification and metabolic processes in many invertebrates (e.g. molluscs, crustaceans and echinoderms) are compromised. This raises questions concerning the potentially broad range of sensitivities to changes in acid-base status amongst invertebrates, as well as concerning the underlying mechanistic origins. Further studies are needed to evaluate potential impacts on noncalcifiers, as well as the synergistic impacts of ocean acidification and global warming. Studies should also focus on the adaptive capability of marine organisms, knowledge that will be crucial to forecast how marine organisms and ecosystems will respond to proceeding world ocean acidification and warming

Seawater carbonate chemistry and resource allocation and extracellular acid-base status in the sea urchin Strongylocentrotus droebachiensis during experiments, 2012

Anthropogenic CO2 emission will lead to an increase in seawater pCO2 of up to 80-100 Pa (800-1000 µatm) within this century and to an acidification of the oceans. Green sea urchins (Strongylocentrotus droebachiensis) occurring in Kattegat experience seasonal hypercapnic and hypoxic conditions already today. Thus, anthropogenic CO2 emissions will add up to existing values and will lead to even higher pCO2 values >200 Pa (>2000 µatm). To estimate the green sea urchins' potential to acclimate to acidified seawater, we calculated an energy budget and determined the extracellular acid base status of adult S. droebachiensis exposed to moderately (102 to 145 Pa, 1007 to 1431 µatm) and highly (284 to 385 Pa, 2800 to 3800 µatm) elevated seawater pCO2 for 10 and 45 days. A 45 - day exposure to elevated pCO2 resulted in a shift in energy budgets, leading to reduced somatic and reproductive growth. Metabolic rates were not significantly affected, but ammonium excretion increased in response to elevated pCO2. This led to decreased O:N ratios. These findings suggest that protein metabolism is possibly enhanced under elevated pCO2 in order to support ion homeostasis by increasing net acid extrusion. The perivisceral coelomic fluid acid-base status revealed that S. droebachiensis is able to fully (intermediate pCO2) or partially (high pCO2) compensate extracellular pH (pHe) changes by accumulation of bicarbonate (maximum increases 2.5 mM), albeit at a slower rate than typically observed in other taxa (10 day duration for full pHe compensation). At intermediate pCO2, sea urchins were able to maintain fully compensated pHe for 45 days. Sea urchins from the higher pCO2 treatment could be divided into two groups following medium-term acclimation: one group of experimental animals (29%) contained remnants of food in their digestive system and maintained partially compensated pHe (+2.3 mM HCO3), while the other group (71%) exhibited an empty digestive system and a severe metabolic acidosis (-0.5 pH units, -2.4 mM HCO3). There was no difference in mortality between the three pCO2 treatments. The results of this study suggest that S. droebachiensis occurring in the Kattegat might be pre-adapted to hypercapnia due to natural variability in pCO2 in its habitat. We show for the first time that some echinoderm species can actively compensate extracellular pH. Seawater pCO2 values of >200 Pa, which will occur in the Kattegat within this century during seasonal hypoxic events, can possibly only be endured for a short time period of a few weeks. Increases in anthropogenic CO2 emissions and leakages from potential sub-seabed CO2 storage (CCS) sites thus impose a threat to the ecologically and economically important species S. droebachiensis

Metabolic suppression during protracted exposure to hypoxia in the jumbo squid, \u3cem\u3eDosidicus gigas\u3c/em\u3e, living in an oxygen minimum zone

The jumbo squid, Dosidicus gigas, can survive extended forays into the oxygen minimum zone (OMZ) of the Eastern Pacific Ocean. Previous studies have demonstrated reduced oxygen consumption and a limited anaerobic contribution to ATP production, suggesting the capacity for substantial metabolic suppression during hypoxic exposure. Here, we provide a more complete description of energy metabolism and explore the expression of proteins indicative of transcriptional and translational arrest that may contribute to metabolic suppression. We demonstrate a suppression of total ATP demand under hypoxic conditions (1% oxygen, PO2=0.8 kPa) in both juveniles (52%) and adults (35%) of the jumbo squid. Oxygen consumption rates are reduced to 20% under hypoxia relative to air-saturated controls. Concentrations of arginine phosphate (Arg-P) and ATP declined initially, reaching a new steady state (~30% of controls) after the first hour of hypoxic exposure. Octopine began accumulating after the first hour of hypoxic exposure, once Arg-P breakdown resulted in sufficient free arginine for substrate. Octopine reached levels near 30 mmol g−1 after 3.4 h of hypoxic exposure. Succinate did increase through hypoxia but contributed minimally to total ATP production. Glycogenolysis in mantle muscle presumably serves to maintain muscle functionality and balance energetics during hypoxia. We provide evidence that post-translational modifications on histone proteins and translation factors serve as a primary means of energy conservation and that select components of the stress response are altered in hypoxic squids. Reduced ATP consumption under hypoxia serves to maintain ATP levels, prolong fuel store use and minimize the accumulation of acidic intermediates of anaerobic ATP-generating pathways during prolonged diel forays into the OMZ. Metabolic suppression likely limits active, daytime foraging at depth in the core of the OMZ, but confers an energetic advantage over competitors that must remain in warm, oxygenated surface waters. Moreover, the capacity for metabolic suppression provides habitat flexibility as OMZs expand as a result of climate change

Impact of ocean warming on the early ontogeny of cephalopods: a metabolic approach

The impact of a realistic warming scenario on the metabolic physiology of early cephalopod (squid Loligo vulgaris and cuttlefish Sepia officinalis) life stages was investigated. During exposure to the warming conditions (19 °C for the western coast of Portugal in 2100), the increase in oxygen consumption rates throughout embryogenesis was much steeper in squid (28-fold increase) than in cuttlefish (11-fold increase). The elevated catabolic activity–accelerated oxygen depletion within egg capsules, which exacerbated metabolic suppression toward the end of embryogenesis. Squid late-stage embryos appear to be more impacted by warming via metabolic suppression than cuttlefish embryos. At all temperature scenarios, the transition from encapsulated embryos to planktonic paralarvae implied metabolic increments higher than 100 %. Contrary to the nektobenthic strategy of cuttlefish newborns, the planktonic squid paralarvae rely predominantly on pulsed jet locomotion that dramatically increases their energy requirements. In the future, hatchlings will require more food per unit body size and, thus, feeding intake success will be crucial, especially for squid with high metabolic rates and low levels of metabolic reserves

Resource allocation and extracellular acid–base status in the sea urchin Strongylocentrotus droebachiensis in response to CO2 induced seawater acidification

Anthropogenic CO2 emission will lead to an increase in seawater pCO(2) of up to 80-100 Pa (800-1000 mu atm) within this century and to an acidification of the oceans. Green sea urchins (Strongylocentrotus droebachiensis) occurring in Kattegat experience seasonal hypercapnic and hypoxic conditions already today. Thus, anthropogenic CO2 emissions will add up to existing values and will lead to even higher pCO(2) values >200 Pa (>2000 mu atm). To estimate the green sea urchins' potential to acclimate to acidified seawater, we calculated an energy budget and determined the extracellular acid base status of adult S. droebachiensis exposed to moderately (102-145 Pa, 1007-1431 mu atm) and highly (284-385 Pa, 2800-3800 mu atm) elevated seawater pCO(2) for 10 and 45 days. A 45-day exposure to elevated pCO(2) resulted in a shift in energy budgets, leading to reduced somatic and reproductive growth. Metabolic rates were not significantly affected, but ammonium excretion increased in response to elevated pCO(2). This led to decreased O:N ratios. These findings suggest that protein metabolism is possibly enhanced under elevated pCO(2) in order to support ion homeostasis by increasing net acid extrusion. The perivisceral coelomic fluid acid-base status revealed that S. droebachiensis is able to fully (intermediate pCO(2)) or partially (high pCO(2)) compensate extracellular pH (pH(e)) changes by accumulation of bicarbonate (maximum increases 2.5 mM), albeit at a slower rate than typically observed in other taxa (10-day duration for full pH(e) compensation). At intermediate pCO(2), sea urchins were able to maintain fully compensated pH(e) for 45 days. Sea urchins from the higher pCO(2) treatment could be divided into two groups following medium-term acclimation: one group of experimental animals (29%) contained remnants of food in their digestive system and maintained partially compensated pH(e) (+2.3 mM HCO3-), while the other group (71%) exhibited an empty digestive system and a severe metabolic acidosis (-0.5 pH units, -2.4 mM HCO3-). There was no difference in mortality between the three pCO(2) treatments. The results of this study suggest that S. droebachiensis occurring in the Kattegat might be pre-adapted to hypercapnia due to natural variability in pCO(2) in its habitat. We show for the first time that some echinoderm species can actively compensate extracellular pH. Seawater pCO(2) values of >200 Pa, which will occur in the Kattegat within this century during seasonal hypoxic events, can possibly only be endured for a short time period of a few weeks. Increases in anthropogenic CO2 emissions and leakages from potential sub-seabed CO2 storage (CCS) sites thus impose a threat to the ecologically and economically important species S. droebachiensis