Cruise Report RV Heincke HE451.1

This cruise was a part of the “Verbundprojekt BIOACID” (Biological Impacts of Ocean ACIDification) Phase II (consortium 4 of 5), funded by the German Ministry for Education and Research (BMBF). It was also connected to the Norwegian-German collaborative project Tibia (“Trophic interactions in the Barents Sea - steps towards an Integrated Ecosystem Assessment (TIBIA)”, see www.caff.is/marine/marine-expert-networks/benthos) between AWI and the IMR in Tromsø. The main objectives of this cruise were to elucidate whether climate change (mainly ocean acidification and warming, OAW) affects interacting species differently due to divergent physiological optima and ranges, expressed in thermal tolerance windows and associated performance capacities and phenologies of specific life stages. To determine the degree of the ongoing ‘Atlantification’ of the waters around (Western) Svalbard, we took sediment samples to analyse the benthic epi- and meiofauna. Further, we intended to obtain specimens of both Polar cod (B. saida) and Atlantic cod (G. morhua) in the Atlantic and polar waters around Svalbard, which were used in experiments on board and back at the Alfred Wegener Institute. We left port in Tromsø in the morning of September 11th, heading North towards Svalbard. In the morning of September 13th, we reached the first scientific station in Hornsund, where a CTD was deployed. Following this, we ran several juvenile fish trawls with fish lift at different depths from surface waters to close to the bottom, specifically aiming for flocks of juvenile fish under the surface, at the thermocline and above ground (water layers of interest derived from CTD and EK60 profiles). In Hornsund, bottom waters were around 0°C cold and contained polar cod (Boreogadus saida). After fishing, we deployed several box grabs for sampling the first 30cm of sediment. This daily sampling protocol was repeated at all other stations unless stated otherwise. After a day of cruising, we reached North East Svalbard and sampled two stations at the center and opening of Rijpfjorden on September 15th and 16th, the protocol here was substantiated by several bottom trawls that yielded surprisingly little material. Afterwards, we moved into Hinlopen Strait, sampling waters of Atlantic and Barents Sea origin in a northwest-southeast transect during September 17th and 18th. The following day found us back in biologically diverse Atlantic waters at the Northwestern tip of Svalbard around Moffen Island, yielding schools of larval/juvenile herring, capelin, redfish and polar cod (and a few 0-class Antlantic cod) in the surface waters as well as a bottom trawl of mostly adult Atlantic cod (Gadus morhua) and several haddock (Melanogrammus aeglefinus). On our way to the AWI Hausgarten, we stopped over on the Yermak plateau on September 20th, where we found similar diversity as the day before. On September 21st, we sampled AWI Hausgarten with CTD, box grabs and several shallow juvenile fish trawls under deteriorating weather conditions. We therefore had to abandon our sampling schedule and the following days found us moving back and forth between shelter in Kongsfjord, Forlandsundet and Krossfjorden and the open water towards the Hausgarten, trying to complete the transect Kongsfjord-Hausgarten. This transect showed a succession of juvenile/larval fish species dominated by redfish (Sebastes sp.) in the open ocean towards Polar cod (B. saida) close to the shore (further abundant species included herring and capelin). Sampling in Forlandsundet revealed a rich and diverse ecosystem with polychaetes, annelids, holothurians, echinoderms and crustaceans (mainly Hyas araneus), again dominated by Atlantic cod (G. morhua). The last stations of the cruise were carried out in Billefjord on September 27th and 28th, here, the very cold bottom waters (-1,7°C) were populated by Polar cod as the only fish species plus several spider crabs (H. araneus). On September 29th, we handed over RV Heincke in Longyearbyen to the chief scientist of HE 451.2, Dr. Katrin Latarius. Thus ended a successful cruise, in which we were able to carry out about 90% of the planned station work, took a great amount of sediment and biological samples and brought around 150 juvenile Polar cod and about 60 juvenile Atlantic cod back to the home institute in Bremerhaven alive

Zell- und systemphysiologische Untersuchungen der Temperaturtoleranz bei Fischen

In an integrative approach, this thesis addressed thermal tolerance in temperate and Antarctic fish examining its functions, limits and mechanistic links between the organismic, cellular and molecular level. The role of oxygen in limiting thermal tolerance of the Antarctic eelpout P. brachycephalum was investigated in in vivo NMR experiments. Temperature effects on respiration, blood flow, intracellular pH and tissue oxygenation were studied under normoxia and hyperoxia. Thermal tolerance was limited by the capacities of the circulatory system supplying oxygen to the tissues. At a lower level of organismic complexity, thermal sensitivity of cellular energy allocation was studied in Antarctic fish. Organismic thermal limitations were not reflected at the cellular level. Provided with sufficient oxygen, cellular energy budgets show greater thermal tolerance than the organism. These findings corroborate that capacity limitations of the organismic level constrict thermal tolerance and support the recent concept of a systemic to molecular hierarchy. At the molecular level, temperature sensitive expression of mitochondrial uncoupling proteins (UCP) was studied during acclimation of P. brachycephalum and the temperate eelpout Z. viviparus. Increased levels of UCP may be necessary to regulate high mitochondrial membrane potentials resulting from unchanged capacities in the warm, possibly indicative of an alternative way of mitochondrial warm adaptation in Antarctic fish. The data demonstrate that thermal tolerance of the various levels of organisation in fish differ when studied alone, but in a complex organism are in control of each other, with the highest organisational level showing highest thermal sensitivity. Within a narrow thermal window, slow warm acclimation of the individual appears possible in Antarctic fish, which in an integrated response of all levels of organisational complexity may shift towards a eurythermal mode of life, thus increasing thermal tolerance

Influence of Temperature, Hypercapnia, and Development on the Relative Expression of Different Hemocyanin Isoforms in the Common Cuttlefish Sepia officinalis

The cuttlefish Sepia officinalis expresses several hemocyanin isoforms with potentially different pH optima, indicating their reliance on efficient pH regulation in the blood. Ongoing ocean warming and acidification could influence the oxygen-binding properties of respiratory pigments in ectothermic marine invertebrates. This study examined whether S. officinalis differentially expresses individual hemocyanin isoforms to maintain optimal oxygen transport during development and acclimation to elevated seawater pCO2 and temperature. Using quantitative PCR, we measured relative mRNA expression levels of three different hemocyanin isoforms in several ontogenetic stages (embryos, hatchlings, juveniles, and adults), under different temperatures and elevated seawater pCO2. Our results indicate moderately altered hemocyanin expression in all embryonic stages acclimated to higher pCO2, while hemocyanin expression in hatchlings and juveniles remained unaffected. During the course of development, total hemocyanin expression increased independently of pCO2 or thermal acclimation status. Expression of isoform 3 is reported for the first time in a cephalopod in this study and was found to be generally low but highest in the embryonic stages (0.2% of total expression). Despite variable hemocyanin expression, hemolymph total protein concentrations remained constant in the experimental groups. Our data provide first evidence that ontogeny has a stronger influence on hemocyanin isoform expression than the environmental conditions chosen, and they suggest that hemocyanin protein abundance in response to thermal acclimation is regulated by post-transcriptional/translational rather than by transcriptional modifications

Temperature tolerance of different larval stages of the spider crab Hyas araneus exposed to elevated seawater PCO2

Introduction: Exposure to elevated seawater PCO2 limits the thermal tolerance of crustaceans but the underlying mechanisms have not been comprehensively explored. Larval stages of crustaceans are even more sensitive to environmental hypercapnia and possess narrower thermal windows than adults. Results: In a mechanistic approach, we analysed the impact of high seawater CO2 on parameters at different levels of biological organization, from the molecular to the whole animal level. At the whole animal level we measured oxygen consumption, heart rate and activity during acute warming in zoea and megalopa larvae of the spider crab Hyas araneus exposed to different levels of seawater PCO2. Furthermore, the expression of genes responsible for acid–base regulation and mitochondrial energy metabolism, and cellular responses to thermal stress (e.g. the heat shock response) was analysed before and after larvae were heat shocked by rapidly raising the seawater temperature from 10°C rearing temperature to 20°C. Zoea larvae showed a high heat tolerance, which decreased at elevated seawater PCO2, while the already low heat tolerance of megalopa larvae was not limited further by hypercapnic exposure. There was a combined effect of elevated seawater CO2 and heat shock in zoea larvae causing elevated transcript levels of heat shock proteins. In all three larval stages, hypercapnic exposure elicited an up-regulation of genes involved in oxidative phosphorylation, which was, however, not accompanied by increased energetic demands. Conclusion: The combined effect of seawater CO2 and heat shock on the gene expression of heat shock proteins reflects the downward shift in thermal limits seen on the whole animal level and indicates an associated capacity to elicit passive thermal tolerance. The up-regulation of genes involved in oxidative phosphorylation might compensate for enzyme activities being lowered through bicarbonate inhibition and maintain larval standard metabolic rates at high seawater CO2 levels. The present study underlines the necessity to align transcriptomic data with physiological responses when addressing mechanisms affected by an interaction of elevated seawater PCO2 and temperature extremes

Mitochondrial acclimation potential to ocean acidification and warming of Polar cod (Boreogadus saida) and Atlantic cod (Gadus morhua)

Background: Ocean acidification and warming are happening fast in the Arctic but little is known about the effects of ocean acidification and warming on the physiological performance and survival of Arctic fish. Results: In this study we investigated the metabolic background of performance through analyses of cardiac mitochondrial function in response to control and elevated water temperatures and PCO2 of two gadoid fish species, Polar cod (Boreogadus saida), an endemic Arctic species, and Atlantic cod (Gadus morhua), which is a temperate to cold eurytherm and currently expanding into Arctic waters in the wake of ocean warming. We studied their responses to the above-mentioned drivers and their acclimation potential through analysing the cardiac mitochondrial function in permeabilised cardiac muscle fibres after 4 months of incubation at different temperatures (Polar cod: 0, 3, 6, 8 °C and Atlantic cod: 3, 8, 12, 16 °C), combined with exposure to present (400μatm) and year 2100 (1170μatm) levels of CO2. OXPHOS, proton leak and ATP production efficiency in Polar cod were similar in the groups acclimated at 400μatm and 1170μatm of CO2, while incubation at 8 °C evoked increased proton leak resulting in decreased ATP production efficiency and decreased Complex IV capacity. In contrast, OXPHOS of Atlantic cod increased with temperature without compromising the ATP production efficiency, whereas the combination of high temperature and high PCO2 depressed OXPHOS and ATP production efficiency. Conclusions: Polar cod mitochondrial efficiency decreased at 8 °C while Atlantic cod mitochondria were more resilient to elevated temperature; however, this resilience was constrained by high PCO2. In line with its lower habitat temperature and higher degree of stenothermy, Polar cod has a lower acclimation potential to warming than Atlantic cod

Oxygen- and capacity-limited thermal tolerance: bridging ecology and physiology

Observations of climate impacts on ecosystems highlight the need for an understanding of organismal thermal ranges and their implications at the ecosystem level. Where changes in aquatic animal populations have been observed, the integrative concept of oxygen- and capacitylimited thermal tolerance (OCLTT) has successfully characterised the onset of thermal limits to performance and field abundance. The OCLTT concept addresses the molecular to whole-animal mechanisms that define thermal constraints on the capacity for oxygen supply to the organism in relation to oxygen demand. The resulting ‘total excess aerobic power budget’ supports an animal’s performance (e.g. comprising motor activity, reproduction and growth) within an individual’s thermal range. The aerobic power budget is often approximated through measurements of aerobic scope for activity (i.e. the maximumdifference between resting and the highest exerciseinduced rate of oxygen consumption), whereas most animals in the field rely on lower (i.e. routine) modes of activity. At thermal limits, OCLTT also integrates protective mechanisms that extend time-limited tolerance to temperature extremes – mechanisms such as chaperones, anaerobic metabolism and antioxidative defence. Here, we briefly summarise the OCLTT concept and update it by addressing the role of routine metabolism.We highlight potential pitfalls in applying the concept and discuss the variables measured that led to the development ofOCLTT.We propose that OCLTTexplains why thermal vulnerability is highest at the whole-animal level and lowest at the molecular level. We also discuss how OCLTT captures the thermal constraints on the evolution of aquatic animal life and supports an understanding of the benefits of transitioning from water to land

ACUTE VS. DEVELOPMENTAL ACCLIMATION SHAPES PARENTAL AND GRANDPARENTAL EFFECTS OF OCEAN WARMING ON MARINE STICKLEBACKS

Transgenerational plasticity (TGP) can buffer populations against rapid environmental change, yet little is known about the underlying mechanisms or how long these effects persist. We tested for adaptive TGP in response to simulated ocean warming across parental and grandparental generations of marine sticklebacks, and investigated mitochondrial respiration capacity (MRC) as a potential mechanism underlying growth responses. Acute exposure to elevated temperature during reproductive conditioning led to strong maternal TGP benefits on F1 offspring growth, with a matching pattern for MRC, providing an intuitive mechanistic basis for maternal acclimation persisting into adulthood. Developmental acclimation to elevated temperature, however, led to negative maternal effects on F2 offspring growth and no detectable maternal effects on MRC. But, maternal grandmother TGP benefits were still present for both growth and MRC, perhaps resulting from epigenetic marks on mitochondrial genes acquired during acute exposure. In summary, both parental and grandparental TGP will play a role in mediating some of the impacts of climate change, but the mechanisms underlying offspring phenotype plasticity may differ depending on whether mothers experience acute or developmental acclimation

Comparative visual and DNA-based diet assessment extends the prey spectrum of polar cod Boreogadus saida

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