Description: Anthropogenic greenhouse gas emissions have been driving global climate change and they will continue to do so over the course of the 21st century. Most of the marine biosphere and especially coastal marine systems have suffered from high anthropogenic pressure per se and it is possible that the novel burden of very rapidly proceeding global climate change triggers shifts to alternative regimes and functioning in marine ecosystems. In the light of this background, my dissertation aims to contribute to the mechanistic understanding of global and local climate change effects on a common coastal marine seaweed (Fucus vesiculosus, Phaeophyceae) system of the Baltic Sea. The results of my experimental studies provide important mechanistic clues about the underlying direct and indirect effective pathways of environmental change in the studied seaweed system. To the best of my knowledge, it is one of the first studies which assess the seasonal variability of the same environmental factors on the same marine system over the course of one year. The detected context-dependency of global climate change effects within one ecosystem clearly shows that our understanding of the basic underlying ecosystem processes and patterns forms a prerequisite for testing, predicting and managing future ecological change in marine systems. Given that grazing forms a crucial ecological force in many coastal vegetated systems, the identified underlying mechanisms of change (top-down and bottom-up control) may allow reference to other similarly structured coastal systems. Importantly my findings point out, that ecological impacts of global climate change may be underestimated if local perturbation is disregarded and, thus, underline the chance and responsibility of local ecosystem management.

Description: The overall aim of my thesis was to improve our understanding of environmental drivers causing the dynamics of the Eastern Baltic cod reproduction habitat and to assess their relevance for a possible application in the sustainable stock management. A novel approach to map the reproductive habitat of Eastern Baltic cod, the Buoyancy Depending Reproductive Layers (BDRL), was developed and used to propose an alternative stock indicator, the effective Spawning Stock Biomass (eSSB). The eSSB was found to improve the fit of a recruitment model compared to the model using the conventional Spawning Stock Biomass. Oxygen depletion was also negatively impacting the available size of nursery areas for juveniles. The mechanism was able to partly explain the observed decline of the condition of juveniles in the nursery areas, because a high population density in the remaining habitat could increase the impact of density depending effects. Furthermore, by the application of the novel approach of BDRLs the spawning habitat was shown to be sensitive to eutrophication and that this sensitivity is strongly depending on the size of the female spawner using the habitat. As predicted, the BDRL approach was superior to the “classic” approach, the Reproductive Volume (RV) because it was more sensitive to environmental change, able to incorporate stock structure, was not overestimating the spawning habitat in the eastern spawning areas and could provide estimates of other stressors depending on the female spawner size. Due to a permanently installed measurement platform in the Arkona Basin, the new methodology could be used to establish a new environmental indicator on the spawning habitat conditions. It was recommended to be used in future stock assessments.

Description: Oceanic emissions of sulfur containing trace gases alter global atmospheric chemistry. The gases act for example as aerosol precursors and change the radiative budget of the Earth, with a significant impact on climate. Large uncertainties exist in the amount of sulfur gases emitted from the ocean, and a gap in the atmospheric budget of carbonyl sulfide – the most abundant sulfur gas in the atmosphere – has been suggested to result from tropical ocean emissions. This thesis uses new shipbased measurements from the tropical Pacific and Indian Ocean together with models to quantify these emissions. Three studies were performed: 1) A 3D model study to test how oceanic emissions can be represented in atmospheric chemistry climate models, 2) A combination of new shipbased data and box model calculation to derive a global emission estimate of carbonyl sulfide and 3) a detailed process study of production processes and their drivers for the gases carbonyl sulfide and carbon disulfide in the Eastern tropical South Pacific. Together, the results yield a new temporally and spatially resolved emission climatology of the three gases.

Description: Multiple global and local stressors threaten populations of the bladderwrack Fucus vesiculosus (Phaeophyceae). Baltic F. vesiculosus populations presumably have a lower genetic diversity compared to other populations. I investigated the adaptive potential under multifactorial environmental change in F. vesiculosus germlings. Effects of warming and acidification were crossed during one year at the two levels “present” and “future” (according to the year 2110) at the “Kiel Outdoor Benthocosms” by applying delta-treatments. Effects of warming varied with season while acidification showed generally weak effects. The two factors “ocean acidification and warming” (OAW) and nutrients were crossed showing that nutrient enrichment mitigated heat stress. Germlings previously treated under the OAW x nutrient experiment were subsequently exposed to a simulated hypoxic upwelling. Sensitivity to hypoxia was enhanced by the previous OAW conditions. Difference in the performance of genetically different sibling groups and diversity level were observed indicating an increased adaptive potential at higher genetic diversity. Different sibling groups were analysed under multiple factors to test correlations of genotypic sensitivities. Sensitivity towards warming, acidification and nutrient enrichment correlated positively while sensitivities towards OAW and hypoxia showed a negative correlation demonstrating that genotypes previously selected under OAW are sensitive to hypoxic upwelling. In a literature review, responses of marine organisms to climate change were analysed through different levels of biological organisation showing that climate change has different effects on each single level of biological organisation. This study highlights that global change research requires an upscaling approach with regard to multiple factors, seasons, natural fluctuations, different developmental stages and levels of biological organisation in the light of the adaptive potential.

Description: Coastal ecosystems worldwide are experiencing increasing anthropogenic pressure, mainly caused by growing human populations in near-shore urban areas and by the rising number of megacities. One of the consequences of this process is the eutrophication of marine habitats that lie in the vicinity of rivers carrying high loads of nutrients that come from agriculture and human sewage. The capital of the Republic of Indonesia, Jakarta, is an example of a megacity impacting the adjacent marine ecosystems: In Jakarta Bay excessive loads of nutrients cause frequent phytoplankton blooms and the resulting microbial activity causes hypoxia events. One of the few species that copes well with these conditions is the Asian green mussel Perna viridis. It forms dense aggregations on bamboo settlement stakes in the bay located within the native distributional range of the mussel that is also a well-known invader of coastal habitats. Non-native populations of this species exist in southern Japan, at some Pacific islands and in the West Atlantic. In Indonesia, P. viridis is native to the western parts of the archipelago but non-native to the eastern parts and was found in the non-native range as fouling on ships that cross the Indonesian archipelago from west to east. One of the reasons for its invasion success is the ability of P. viridis to tolerate large fluctuations in abiotic environmental conditions. Therefore, understanding the factors influencing the mussel’s tolerance to environmental stress, should help to understand their invasion success. To address this question, I conducted three studies in which I exposed mussels to hypoxia in the laboratory under different scenarios. In the first study, I compared the hypoxia tolerance and nutritional status of mussels collected from a ship hull in the non-native range to those of mussels from Jakarta Bay in the native range. I found that the mussels collected from the ship hull were in a very poor nutritional status and tolerated hypoxia in the laboratory only half as long as mussels from the eutrophic Jakarta Bay. The finding suggests that transport on a ship hull may reduce the invasion potential of the species if the journey leads through areas of low food supply. The other two studies that comprise this thesis aim at assessing the potential roles of local adaptations (i.e. an irreversible modification that is manifested in the gene pool of a population), acclimation to stress (i.e. a reversible modification that is not genetically manifested) and a good nutritional status (caused by ample planktonic food supply in a eutrophic habitat) in determining the degree of tolerance to environmental stress in mussels. The idea of investigating this closer had arisen from a previous study, which found that individuals from Jakarta Bay are more tolerant to environmental stress (i.e. salinity, thermal and oxygen stress) than conspecifics from a more natural habitat in Indonesia. However, it remained unknown which mechanisms led to this difference. I approached this question by conducting a reciprocal transplantation experiment and subsequent hypoxia tests in the laboratory with P. viridis from the eutrophic Jakarta Bay and an oligotrophic habitat in West Java. The experiment showed that tolerance to hypoxia was rather determined by the conditions in the habitat where the mussels had lived for two months after transplantation before exposure to stress and not by the characteristics of the habitat where they originated from. This suggests that local adaptations to stress did not occur in Jakarta Bay mussels - although they have a long history of experiencing adverse conditions – or that they have been overwritten by other determinants of tolerance to hypoxia. The main determinant of stress tolerance again was the nutritional status. In the third study of this thesis, I conducted experiments that allowed establishing a causal relationship between a high nutritional status and hypoxia tolerance. Jakarta Bay mussels that had obtained more food supply in the laboratory had a better hypoxia tolerance than Jakarta Bay mussels that had obtained less food and were in a poor nutritional status. Furthermore, acclimation to low, non-lethal concentrations of dissolved oxygen enhanced hypoxia tolerance in mussels with low nutritional states. Taken together, these results show that a good nutritional status is the most relevant determinant of tolerance to environmental stress in P. viridis, which implies that the mussel can benefit from eutrophication caused by anthropogenic impact. Perna viridis may, therefore, be a species that can extend its distributional range if anthropogenic pressure in urban, near-shore areas is increasing and contributing to eutrophication. However, it may not succeed and establish in more non-native areas if conservation efforts apply that keep tropical and subtropical coastal ecosystems in an oligotrophic state and maintain high levels of biodiversity.

Description: Poseidon cruise 518 (leg 1 and 2) took place in the framework of the Horizon 2020 project STEMM-CCS of the EU. The project’s main goal is to develop and test strategies and technologies for the monitoring of subseafloor CO2 storage operations. In this context a small research-scale CO2 gas release experiment is planned for 2019 in the vicinity of the Goldeneye platform located in the British EEZ (central North Sea). Cruise POS518 aimed at collecting necessary oceanographic and biogeochemical baseline data for this release experiment. During Leg 1 ROV PHOCA was used to deploy MPI’s tool for high-precision measurements of O2, CO2 and pH in the bottom water at Goldeneye. In addition, ROV push cores and gravity cores were collected in the area for sediment biogeochemical analyses, and video-CTD casts were conducted to study the water column chemistry. The stereo-camera system and a horizontally looking multibeam echosounder, both, for determining gas bubble emissions at the seafloor were deployed at the Figge Maar blowout crater in the German Bight. Investigations were complemented by hydroacoustic surveys detecting gas bubble leakages at several abandoned wells in the North Sea as well as the Figge Maar. Surface water alkalinity as well as CH4, CO2, and water partial pressures in the air above the sea surface were measured continuously during the cruise. During Leg 2 three different benthic lander systems were deployed to obtain baseline data of oceanographic and biogeochemical parameters for a small research-scale CO2 gas release experiment planned for 2019. The first lander was equipped with an acoustic Doppler current profiler (ADCP), a CTD and an O2 optode. It was deployed for 6 days close to Goldeneye to obtain high resolution data which can be linked to the long-term measurements of the NOC-Lander. This lander is equipped with a suite of sensors to monitor temperature, conductivity, pressure, current speed and direction, hydro-acoustic, pH, pCO2, O2 and nutrients over a period of about 10 months with popup telemetry units for data transmission via IRIDIUM satellite telemetry every 3 months. Two short-term deployments of the Biogeochemical Observatory (BIGO) were conducted to study the molar ratio between oxygen and CO2-fluxes at the seafloor. Sediment cores obtained by gravity and multi corer were collected for sediment biogeochemical analyses and video-CTD casts were used to study the chemistry of the water column.

Description: The ever-increasing complexity of in silico experiments in computational science is reflected in the growing complexity of the simulation software enabling these experiments. However, computational scientists rarely employ state-of-the-art software engineering methods, which negatively affects their productivity as well as the reliability of their scientific results. To tackle this challenge, this book introduces the Sprat Approach, which hierarchically integrates multiple domain-specific languages to facilitate the cooperation of scientists from different disciplines and to support them in creating well-engineered software without extensive software engineering training. To evaluate the Sprat Approach, it is applied to the implementation of the Sprat Marine Ecosystem Model in an exploratory case study. The Sprat Marine Ecosystem Model is a novel end-to-end ecosystem model based on population balance equations. In order to evaluate the Sprat Model, it is parametrized for the eastern Scotian Shelf ecosystem with its intertwined direct and indirect fish stock interactions, which previously could not be modeled satisfactorily. The simulation results described in this book provide new insights into the main drivers of regime shifts in marine ecosystems.

Description: Over the last two centuries human activities significantly changed the Earth system. Atmospheric CO2 concentrations were increased by ~25% in only 50 years (1965 to 2015) through combustion of fossil fuels and changes in land use. Consequences of these activities are a warming climate and the ‘acidification’ of the world oceans. A doubling of surface ocean carbon dioxide- (CO2) and proton- (H+) and a 40% decrease of the carbonate ion (CO32-) concentrations until the end of this century will probably affect many marine organisms. Due to low temperatures, the Arctic Surface Ocean will be one of the first to experience mean annual corrosive conditions for calcified organisms. This makes the Arctic Ocean a bellwether for global impacts of ocean acidification (OA) on marine life. Biogenic calcium carbonate often establishes ecological functions like being the fundament for species rich habitats in the case of hermatypic corals and crustose coralline algae (CCA) or impacting global carbon cycling embodied by coccolithophores, foraminifera and thecosome pteropods. The marine carbon cycle influences the destination of human CO2 emissions and the development of the global climate. Therefore, the ecological importance of CCA and pteropods, their involvement in the marine carbon cycle and their anticipated vulnerability to OA call for research on their fate in the future ocean. This doctoral thesis investigates the effects of warming and ocean acidification on growth, calcification, dissolution, corrosion and survival of Arctic calcifying keystone species Lithothamnion glaciale (CCA) and Limacina helicina and retroversa (thecosome pteropods).

Description: Ecosystems all over the world are continuously invaded by new species, which become non-indigenous species (NIS) in the new location. Increasing ship traffic raises the chances for relocations of aquatic species to new regions since shipping is identified as the major transport vector. This dissertation focused on NIS from the North and Baltic Seas and the Great Lakes-St. Lawrence River region. Both regions are connected via frequent transatlantic ship traffic and highly invaded by well documented NIS. Comparing origins of established aquatic NIS in both regions revealed that the systems are highly invaded by species that originate from the Ponto-Caspian region which consists of the Black, Azov and Caspian Seas. Further, observed numbers of established NIS in the two regions were compared to expected numbers of NIS from major donor regions based on the available species pool from donor regions, frequency of shipping transit, and an environmental match between donor and recipient regions. It was discovered that Ponto-Caspian taxa colonized both regions in much higher numbers than expected (Chapter I). A comprehensive study of seven life history traits for each NIS in both regions revealed that certain traits such as dormancy, regeneration and r-strategy are potentially beneficial for invasion success (Chapter II). Global warming as part of a predicted climate change might become a hazard for the survival of some native species, especially in coastal zones which is the habitat of amphipods. Environmental tolerance towards changing temperatures was investigated in three amphipod species and the results revealed that the Ponto-Caspian species Pontogammarus maeoticus has a higher temperature tolerance, especially towards rising temperatures, compared to Gammarus oceanicus, which is native to the Baltic Sea (Chapter III). Hence, with predicted global warming Ponto-Caspian species might be able to compete against native species in the Baltic Sea.