Effekte von Ozeanversauerung auf Larven des Atlantischen Dorsch (Gadus morhua)

Throughout the twentieth and the beginning of the twenty-first century technical advancements in many industries as well as the vast increase in world population have led to increasing emissions of greenhouse gases like carbon dioxide. The changes in the chemistry of the atmosphere not only result in retention of heat causing global warming, but also transfer to the oceans. The world’s oceans are not only warming, but are furthermore acidifying through the reaction of seawater with carbon dioxide, measured in pH and termed ocean acidification. The aim of this thesis was to provide greater understanding of the impact of ocean acidification on one of the most important commercial species, the Atlantic cod (Gadus morhua) and to provide a quantitative foundation to evaluate recruitment processes of this species. This thesis has quantified the effect of ocean acidification on larval survival of two Atlantic cod stocks from the Western Baltic Sea and the Barents Sea and how this translates into the recruitment of these populations. Additionally, the effect of acidification and its interaction with food availability on larval growth was quantified for the Barents Sea cod. In order to investigate the potential for adaptation or acclimation, it was furthermore explored whether the acclimation of the parental generation to acidification had a significant effect on larval survival and organ development. The results of this dissertation demonstrate that ocean acidification may pose a severe threat to Atlantic cod populations. Nonetheless, the exact effects are very complex and rely on other factors, like the exposure of the parental generation to acidification and on food availability to the larvae.Im Verlauf des zwanzigsten und dem Beginn des einundzwanzigsten Jahrhunderts haben der technische Fortschritt in Verbindung mit einem starken Zuwachs in der Weltbevölkerung zu einem hohen Anstieg der Emissionen von Treibhausgasen wie Kohlenstoffdioxid geführt. Änderungen in der Chemie der Atmosphäre führen nicht nur zu Wärmerückhaltung und Klimawandel, sondern auch zu Änderungen in der Meereschemie. Die Weltmeere erwärmen sich nicht nur, sondern versauern auch durch die Reaktion des Seewassers mit Kohlenstoffdioxid. Dieser Prozess, gemessen in pH, heißt Ozeanversauerung. Das Ziel dieser Dissertation ist ein besseres Verständnis des Einflusses von Ozeanversauerung auf eine der kommerziell genutztesten Fischarten, den Atlantischen Dorsch (Gadus morhua), zu erreichen und eine quantitative Basis zu legen um Änderungen in den Rekrutierungsprozessen dieser Art zu bewerten. Diese Dissertation quantifiziert den Effekt von Ozeanversauerung auf das Überleben von Larven von zwei Populationen des Atlantischen Dorschs aus der westlichen Ostsee und der Barentssee und zeigt, wie sich dieses auf die Rekrutierung auswirkt. Zusätzlich wurden die Auswirkungen von der Ozeanversauerung und die Wechselwirkungen mit Nahrungsverfügbarkeit auf das Larvenwachstum des Barentssee Bestandes quantifiziert. Um das Potential zur Adaptation oder Akklimatisierung der Larven zu untersuchen, wurden die Auswirkungen einer Akklimatisierung der Elterngeneration an die Versauerung auf das Überleben der Larven und ihrer Organentwicklung ermittelt. Die Ergebnisse dieser Dissertation belegen, dass Ozeanversauerung eine große Bedrohung für die Bestände des Atlantischen Dorsches darstellen kann. Nichtsdestotrotz sind die genauen Auswirkungen sehr komplex und hängen von vielen Faktoren ab, wie beispielsweise die Anpassung der Elterngeneration an die Ozeanversauerung und die Nahrungsverfügbarkeit der Larven

Effects of Ocean Acidification on Atlantic Cod Larvae (Gadus morhua)

Throughout the twentieth and the beginning of the twenty-first century technical advancements in many industries as well as the vast increase in world population have led to increasing emissions of greenhouse gases like carbon dioxide. The changes in the chemistry of the atmosphere not only result in retention of heat causing global warming, but also transfer to the oceans. The world’s oceans are not only warming, but are furthermore acidifying through the reaction of seawater with carbon dioxide, measured in pH and termed ocean acidification. The aim of this thesis was to provide greater understanding of the impact of ocean acidification on one of the most important commercial species, the Atlantic cod (Gadus morhua) and to provide a quantitative foundation to evaluate recruitment processes of this species. This thesis has quantified the effect of ocean acidification on larval survival of two Atlantic cod stocks from the Western Baltic Sea and the Barents Sea and how this translates into the recruitment of these populations. Additionally, the effect of acidification and its interaction with food availability on larval growth was quantified for the Barents Sea cod. In order to investigate the potential for adaptation or acclimation, it was furthermore explored whether the acclimation of the parental generation to acidification had a significant effect on larval survival and organ development. The results of this dissertation demonstrate that ocean acidification may pose a severe threat to Atlantic cod populations. Nonetheless, the exact effects are very complex and rely on other factors, like the exposure of the parental generation to acidification and on food availability to the larvae

Ocean warming and acidification may drag down the commercial Arctic cod fishery by 2100

The Arctic Ocean is an early warning system for indicators and effects of climate change. We use a novel combination of experimental and time-series data on effects of ocean warming and acidification on the commercially important Northeast Arctic cod (Gadus morhua) to incorporate these physiological processes into the recruitment model of the fish population. By running an ecological-economic optimization model, we investigate how the interaction of ocean warming, acidification and fishing pressure affects the sustainability of the fishery in terms of ecological, economic, social and consumer-related indicators, ranging from present day conditions up to future climate change scenarios. We find that near-term climate change will benefit the fishery, but under likely future warming and acidification this large fishery is at risk of collapse by the end of the century, even with the best adaptation effort in terms of reduced fishing pressure.publishedVersio

Environmental influences on Norwegian spring-spawning herring (<i>Clupea harengus</i> L.) larvae reveal recent constraints in recruitment success

The lack of any abundant recruiting year class of Norwegian spring-spawning (NSS) herring between 2005 and 2015 contributed to an approximate reduction of 40% in the spawning-stock biomass since 2009, i.e. from 7 to 4 million tonnes. Warming of the North Atlantic is suggested to contribute to this reduction in recruitment. In the past, a warm phase induced by a positive Atlantic Multidecadal Oscillation (AMO) in the North Atlantic was positively correlated to the NSS herring stock size. Recent unprecedented ocean warming in the Norwegian Sea ecosystem, besides elevated temperatures due to a positive AMO, seems to be outside optimal environmental conditions for early life history stages of NSS herring. We analysed 28 years of survey data using generalized additive models to reconstruct environmental conditions for drifting yolksac and preflexion stage larvae. Our results indicate that strong recruitment years were more likely when the larvae occurred simultaneously with a negative AMO during positive temperature anomalies. The transition from yolksac stages towards preflexion stages occurred while there was a slow increase in water temperature during the larval drift. Weak recruitment years generally occurred when larvae experienced elevated temperatures during the life stage transition under a positive AMO. These results augment evidence that the historical positive relationship between AMO and stock dynamics is reversed between 1988 and 2015. Albeit not implying any specific mechanistic biological interactions, we can assume that the unprecedented warming has modified the ecosystem drivers that negatively affect drifting larvae. Since 2016, the North Atlantic is shifting into a negative AMO phase, possibly resulting in the 10-year recruitment suppression of NSS herring ending soon.publishedVersio

Ocean Acidification Effects on Atlantic Cod Larval Survival and Recruitment to the Fished Population

-How fisheries will be impacted by climate change is far from understood. While some fish populations may be able to escape global warming via range shifts, they cannot escape ocean acidification (OA), an inevitable consequence of the dissolution of anthropogenic carbon dioxide (CO2) emissions in marine waters. How ocean acidification affects population dynamics of commercially important fish species is critical for adapting management practices of exploited fish populations. Ocean acidification has been shown to impair fish larvae’s sensory abilities, affect the morphology of otoliths, cause tissue damage and cause behavioural changes. Here, we obtain first experimental mortality estimates for Atlantic cod larvae under OA and incorporate these effects into recruitment models. End-of-century levels of ocean acidification (~1100 μatm according to the IPCC RCP 8.5) resulted in a doubling of daily mortality rates compared to present-day CO2 concentrations during the first 25 days post hatching (dph), a critical phase for population recruitment. These results were consistent under different feeding regimes, stocking densities and in two cod populations (Western Baltic and Barents Sea stock). When mortality data were included into Ricker-type stock-recruitment models, recruitment was reduced to an average of 8 and 24% of current recruitment for the two populations, respectively. Our results highlight the importance of including vulnerable early life stages when addressing effects of climate change on fish stocks

Pilot study to investigate the effect of long-term exposure to high pCO2 on adult cod (Gadus morhua) otolith morphology and calcium carbonate deposition

Funding was provided by the Bonus Baltic Sea research and development programme (Art 185) BIO-C3 project, funded jointly by the EU and the BMBF (Grant No. 03F0682A), BIOACID project (Biological Impacts of Ocean Acidification: Grant No. 03F0655K) funded by the German Ministry for Education and Research (BMBF), and the EU AQUAEXCEL transnational access grant for aquaculture infrastructures. Part of the work was supported by the FINEAQUA-project (Grant Number 12212001) funded by the Program for the Future Economy (financed by the European Regional Development Fund, the Federal Republic of Germany and the state of Schleswig–Holstein), the Centre for Marine Aquaculture, Tromsø, and the Marine Alliance for Science and Technology for Scotland (MASTS) Small Grant initiative (SG330 and SG407), and their support especially by the staff of the centre for Marine Aquaculture is gratefully acknowledged. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions. PBW would like to thank the Royal Society for the award of an Industry Fellowship. DGS is a Serra Húnter Tenure-Track lecturer.To date the study of ocean acidification on fish otolith formation has been mainly focused on larval and juvenile stages. In the present pilot study, wild-captured adult Atlantic cod (Gadus morhua) were exposed to two different levels of pCO2, 422µatm (ambient, low pCO2) or 1091µatm (high pCO2), for a period of 30 weeks (from mid-October to early April 2014–2015) in order to study the effects on otolith size, shape and CaCO3 crystallization amongst other biological parameters. We found that otoliths from cod exposed to high pCO2 were slightly smaller (− 3.4% in length; − 3.3% in perimeter), rounder (− 2.9% circularity and + 4% roundness) but heavier (+ 5%) than the low pCO2 group. Interestingly, there were different effects in males and females; for instance, male cods exposed to high pCO2 exhibited significant changes in circularity (− 3%) and roundness (+ 4%) compared to the low pCO2 males, but without significant changes on otolith dimensions, while females exposed to high pCO2 had smaller otoliths as shown for length (− 5.6%), width (− 2%), perimeter (− 3.5%) and area (− 4.8%). Furthermore, while the majority of the otoliths analysed showed normal aragonite deposition, 10% of fish exposed to 1091µatm of pCO2 had an abnormal accretion of calcite, suggesting a shift on calcium carbonate polymorph crystallization in some individuals under high pCO2 conditions. Our preliminary results indicate that high levels of pCO2 in adult Atlantic cod might affect otolith growth in a gender-specific way. Our findings reveal that otoliths from adult cod are affected by ocean acidification, and we believe that the present study will prompt further research into this currently under-explored areaPublisher PDFPeer reviewe

Divergent responses of Atlantic cod to ocean acidification and food limitation

In order to understand the effect of global change on marine fishes, it is imperative to quantify the effects on fundamental parameters such as survival and growth. Larval survival and recruitment of the Atlantic cod (Gadus morhua) were found to be heavily impaired by end-of-century levels of ocean acidification. Here, we analysed larval growth among 35–36 days old surviving larvae, along with organ development and ossification of the skeleton. We combined CO2treatments (ambient: 503 µatm, elevated: 1,179 µatm) with food availability in order to evaluate the effect of energy limitation in addition to the ocean acidification stressor. As expected, larval size (as a proxy for growth) and skeletogenesis were positively affected by high food availability. We found significant interactions between acidification and food availability. Larvae fed ad libitum showed little difference in growth and skeletogenesis due to the CO2 treatment. Larvae under energy limitation were significantly larger and had further developed skeletal structures in the elevated CO2 treatment compared to the ambient CO2 treatment. However, the elevated CO2 group revealed impairments in critically important organs, such as the liver, and had comparatively smaller functional gills indicating a mismatch between size and function. It is therefore likely that individual larvae that had survived acidification treatments will suffer from impairments later during ontogeny. Our study highlights important allocation trade-off between growth and organ development, which is critically important to interpret acidification effects on early life stages of fish

Transcriptome profiling reveals exposure to predicted end-of-century ocean acidification as a stealth stressor for Atlantic cod larvae

Ocean acidification (OA), a direct consequence of increasing atmospheric CO2 concentration dissolving in ocean waters, is impacting many fish species. Little is known about the molecular mechanisms underlying the observed physiological impacts in fish. We used RNAseq to characterize the transcriptome of 3 different larval stages of Atlantic cod (Gadus morhua) exposed to simulated OA at levels (1179 µatm CO2) representing end-of-century predictions compared to controls (503 µatm CO2), which were shown to induce tissue damage and elevated mortality in G. morhua. Only few genes were differentially expressed in 6 and 13 days-post-hatching (dph) (3 and 16 genes, respectively), during a period when maximal mortality as a response to elevated pCO2 occurred. At 36 dph, 1413 genes were differentially expressed, most likely caused by developmental asynchrony between the treatment groups, with individuals under OA growing faster. A target gene analysis revealed only few genes of the universal and well-defined cellular stress response to be differentially expressed. We thus suggest that predicted ocean acidification levels constitute a “stealth stress” for early Atlantic cod larvae, with a rapid breakdown of cellular homeostasis leading to organismal death that was missed even with an 8-fold replication implemented in this study

Effects of parental acclimation and energy limitation in response to high CO2 exposure in Atlantic cod

Ocean acidification (OA), the dissolution of excess anthropogenic carbon dioxide in ocean waters, is a potential stressor to many marine fish species. Whether species have the potential to acclimate and adapt to changes in the seawater carbonate chemistry is still largely unanswered. Simulation experiments across several generations are challenging for large commercially exploited species because of their long generation times. For Atlantic cod (Gadus morhua), we present first data on the effects of parental acclimation to elevated aquatic CO2 on larval survival, a fundamental parameter determining population recruitment. The parental generation in this study was exposed to either ambient or elevated aquatic CO2 levels simulating end-of-century OA levels (~1100 µatm CO2) for six weeks prior to spawning. Upon fully reciprocal exposure of the F1 generation, we quantified larval survival, combined with two larval feeding regimes in order to investigate the potential effect of energy limitation. We found a significant reduction in larval survival at elevated CO2 that was partly compensated by parental acclimation to the same CO2 exposure. Such compensation was only observed in the treatment with high food availability. This complex 3-way interaction indicates that surplus metabolic resources need to be available to allow a transgenerational alleviation response to ocean acidification