Description: Glacial isostatic adjustment (GIA) is the ongoing response of the viscoelastic solid Earth, oceans and the gravitational field to the previous burden of the ice loads. The Earth’s surface was once covered with massive ice sheets, and melting of these ice sheets is still reshaping coastlines and affecting sea-level. To reconstruct former sea level and be able to predict future changes, it is necessary to constrain the rheological properties of the Earth’s structure. Widely used data to constrain Earth’s interior are sea-level indicators. In the first part of the thesis, we propose a statistical method that quantifies a relationship between the sea-level indicator and a relative sea level in order to compare it to GIA predictions. A statistical method is based on consideration of spatial and temporal probability density functions, derived from the age and elevation of each indicator. This method allows a more rigorous approach to validation with sea-level data and possibility to include low-quality data. We verified method performance in the Hudson Bay, Canada as a test run before applying it to the SW Fennoscandia. SW Fennoscandia identifies as an area where lateral heterogeneity is likely to exist. The south-western part of Fennoscandia lies on the crustal boundary called the Trans-European Suture Zone (TESZ), or the Tornquist Zone. GIA models have two representations of Earth’s structure; radially symmetric (1D), where the rheology only varies vertically, and lateral or 3D variations of viscosity structure. In this thesis, we compare glacial isostatic adjustment reconstructions with both representations of the rheology. Results from the 1D model show variations in the viscosity structure between the area near to the centre of the former ice sheet and the areas at the margin of the ice sheet. Hence, we verify the importance of including lateral variations in GIA models in this region. Application of 3D models displays the sensitivity of model parameters to crustal deformation. German Baltic coast yields thinner lithosphere than TESZ region and near-centre region. Additionally, in the TESZ region, we notice a steep increase in viscosity of the asthenosphere and upper-mantle. Furthermore, we compared two different global ice histories (ICE5G and ICE6G_C) and concluded that the marginal areas are more sensitive to different deglaciations, and we propose to use regional ice histories to constrain GIA models better. Apart from the new statistical method, this study sets a ground for future GIA studies in complex tectonic regions and demonstrates the importance of including laterally heterogeneous Earth structure in GIA models.

Description: The Asian brush clawed shore crab Hemigrapsus takanoi is native to the north-western Pacific Ocean. Since the 1990s, H. takanoi is known to invade the intertidal zones of the European Atlantic and the North Sea coasts, where this species shares habitats with for example the native European green crab Carcinus maenas, and competition in habitat and food sources between both species was observed. H. takanoi was first detected in the Baltic Sea in summer 2014. Numerous juveniles and adults including ovigerous females were observed from its south-western region (most inner part of the Kiel Fjord). Gaining knowledge about population structure of a recently introduced species and its interactions with the biodiversity in its recipient habitat is crucial to assess the effects on the ecosystem. In addition, information of factors promoting its invasion and establishment success is important to predict future invasion potential and extension ranges. Thus, the main scope of this thesis is 1) to evaluate the current status of H. takanoi in south-western Baltic Sea Kiel Fjord, 2) to gain insights into the tolerance of different life history stages to salinity stress, 3) to assess larval responses to climate driven environmental variables, more specifically, on how tolerance to low salinity regimes is affected by increasing seawater temperature. Up to 596 H. takanoi adult specimens were found from the inner Kiel Fjord during monitoring in 2017. Although males reached larger sizes than females, with sizes up to 29 mm compared to 25.5 mm for females, females were more abundant than males. Reproductive season started in June and lasted into August. The current study investigated that, the relatively large claws of males comparing to females, helped them to open mussels of Mytilus edulis up to a size of 18.1‒21.0 mm, while the largest size opened by females was up to 12.1‒15.0 mm only. In addition, males consumed twice as much as mussel biomass compared to females of similar sizes. Consumption rates for both sexes increased by increasing temperatures over seasonal changes. Performance of H. takanoi towards a wide salinity gradient was different among the different life history stages. Early life history stages were more vulnerable than juveniles and adults. Fitness parameters, represented by consumption rates on M. edulis, of juveniles and adults, showed a significant positive correlation with increasing salinity. For adults, feeding was highest at a salinity of 25. However, larvae showed low resistance to lower salinities, and failure in development to megalopa at salinity below 16, which represents the current Kiel Fjord mean salinity conditions over the year. In general, survival to megalopa increased with increasing salinity under the examined salinity treatments (salinities of 0‒35 and 10‒25 during the 2017 and 2018 experiments, respectively). The highest numbers of megalopa were recorded at salinity 25. The results of this thesis show that H. takanoi is able to complete its entire life cycle in the brackish Kiel Fjord, however, its sensitivity to low salinity might be a barrier for their further spread towards the Baltic Proper. In addition, the result revealed that intrapopulation variability, seen in the offspring of only one out of five females that succeeded to reach the megalopa at a salinity of 16, might potentially be the reason for H. takanoi population persistence in Kiel Fjord. H. takanoi early life history stages have been shown to suffer predicted near-future climate change and were affected by the tested multiple stressors (salinity and temperature). There were no interaction effects of temperature and salinity on larval survival and their time to reach the megalopa. Nevertheless, increased temperature accelerates their development and raised larval mortality at all salinity levels. At higher temperature, no larvae reach megalopa below salinity of 19. In conclusion, H. takanoi successfully established a population in the south-western Baltic Sea (inner Kiel Fjord) and will most likely add more pressure on M. edulis compared to conditions before their arrival. The species showed an ontogenetic shift in response to salinity with development. Tolerance to low salinity is likely a key determinant for H. takanoi’s further spread throughout the whole Baltic Sea today and in future conditions.

Description: Seamounts, such as the Ewing Seamount in the south-east Atlantic, offer a habi- tat for Vulnerable Marine Ecosystems (VMEs) with increased biological activity compared to the surrounding deep sea. This is due to characteristic circulation features, such as a ’Taylor cap’ with a horizontal anticyclonic cell and vertical cir- culation cells that transport nutrient-rich water from the depths to the slopes and summit of the seamount. With the help of ocean model data and Lagrangian simu- lations, favourable conditions for marine species can be observed and quantified. One method for this is the description of the ’retention potential’, the likelihood of particles, for example nutrients or larvae, to remain in a certain area. Experiments with Parcels were carried out to investigate how the different model formulations and resolutions of INALT20 and ROMS-AGRIF affect the particle spreading at the Ewing Seamount. These model configurations differ both in the horizontal and ver- tical resolution, the formulation of the vertical axis and the atmospheric and tidal forcing. With coarser resolution and a vertical axis with levels of constant depth, there is no anticyclonic cell around the summit. Additionally, velocities near the bathymetry are generally low compared to when using terrain-following coordi- nates. As a result, particles are carried away from the seamount at a slower rate, which increases the retention potential. Tides, in turn, reduce this potential, and an atmospheric forcing with interannual variability contributes to greater variabil- ity in the particle distribution.

Description: The work within this doctoral thesis introduces the Caribbean reef fish genus Hypoplectrus (hamlets) into the field of speciation genomics. The overarching theme within this thesis is the investigation of the underlying evolutionary drivers that are acting at the origin of this marine radiation and facilitate rapid speciation within the ocean. Distributed over four separate manuscripts, this work addresses several aspects impacting the dynamics of the Hypoplectrus radiation. Within the first manuscript, the temporal stability of the hamlet community in a patch of reefs in Puerto Rico is investigated. The findings indicate that the hamlet community composition is dynamic and potentially impacted by ecological factors such as turbidity or the presence of specific coral species. Within the second manuscript the hamlet reference genome is introduced and whole genome resequencing is applied to investigate the signals of speciation within three of the most common hamlet species. The results show that, against a genome wide background of very low differentiation, a small number of color pattern and vision genes are highly differentiated between species and apparently co-selected for. The third manuscript explores the demographic history of a rare endemic hamlet species. It uses a coalescent approach to show the decline in population size of this particular species since the recent evolutionary split from the remaining genus. In the last manuscript, nine different hamlet species are sequenced to provide a cross section through the hamlet radiation. The results of population- and phylogenomics indicate ongoing inter-species gene flow throughout the majority of the genome with only a small set of putative barrier genes. Phylogenetic relationships through most of the genome are diffuse, yet the signal within the few differentiated genomic intervals is discordant, pointing to introgession events or differential lineage sorting at those major effect loci.

Description: Some heavy metals e.g., zinc, copper or manganese serve as micronutrients for eukaryotic life and play an important role for the cellular metabolism, growth of organisms, reproduction and enzymatic activity. However, other metals like mercury or lead are not known to have any beneficial effects for organisms and are believed to have a higher toxic potential. Heavy metals occur naturally in the environment. However, in higher concentrations, they become toxic and have hazardous effects on marine biota. Furthermore, they are highly persistent in the marine environment as they are not readily degraded by organisms. Pollution originating from anthropogenic sources, e.g., mining, industry and extensive land use, increased the heavy metal concentration in certain areas above a critical level. Especially temperate and tropical coastal environments act as natural catchment for anthropogenic pollutants because these areas are densely populated and highly affected by industry, agriculture and urban runoff. Therefore, it is vitally important to assess past heavy metal distributions, spatially and temporally and to compare those with recent pollution in order to evaluate contemporary emission reduction measures. The chemistry of the tests of benthic foraminifera and the skeletons of scleractinian corals are widely used for the reconstruction of changes in past environmental conditions including temperature, salinity and carbonate system parameters. Recent studies further demonstrated that the trace metal concentration in the aragonite of corals and the calcite of foraminifera is linked to that in seawater. Therefore, the geochemical analysis of coral skeletons and foraminiferal tests offers the opportunity to gain insights into past heavy metal concentrations in seawater, which can in turn help to improve coastal management. However, it is important to understand distribution patterns, ecological and environmental factors influencing the organism itself and associated species in order to evaluate which species is suitable and representative for a certain area. Therefore, the living and dead foraminiferal assemblage along a transect in the German North Sea was investigated. The results of this study indicate that transport via tidal currents is the dominant environmental factor shaping the foraminiferal assemblages. Haynesina germanica, Ammonia batava and different Elphidium species from the living foraminiferal fauna depict a close linkage between open North Sea areas like Helgoland and the mainland. These species share an opportunistic behaviour and are able to occupy a variety of environments rendering them as possible proxy-carriers for heavy metal contamination in seawater. Nevertheless, an application of the heavy metal concentration in the calcium carbonate of both of the organism groups will only be possible after a calibration of this proxy. Therefore, benthic foraminifera from temperate environments (Ammonia aomoriensis, Ammonia batava and Elphidium excavatum) and tropical corals (Porites lichen and Porites lobata) were exposed to a mixture of dissolved chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), silver (Ag), cadmium (Cd), tin (Sn), mercury (Hg) and lead (Pb) over a wide concentration range. High frequency water monitoring in combination with laser ablation ICP-MS measurements of the calcium carbonate, which was precipitated during the culturing period, revealed the uptake of some of these metals mainly depends on its concentration in seawater, which is indicated by strong positive correlations between the metal concentration in seawater and in the calcium carbonate. All three foraminiferal species showed a strong positive correlation between Pb and Ag in the water and their calcite. Ammonia aomoriensis further revealed a correlation with Mn and Cu, Ammonia batava with Mn and Hg and Elphidium excavatum with Cr and Ni, and partially also with Hg. Zinc, Sn and Cd showed no clear trends in all three foraminiferal species studied, which in case of Cd may be due to the exposure to more than one metal at a time. The investigated coral species revealed a positive correlation between the trace metal concentration in seawater and in the coral skeleton for Cr, Mn, Ni, Zn, Ag, Cd and Pb. No correlation was found for Cu, Sn and Hg. The calculated partitioning coefficients (DTE) allow a determination of the heavy metal concentrations in seawater. Therefore, the trace element concentration in benthic foraminifera and in scleractinian corals provides a promising tool for ecosystem status assessments in the future, which can serve as a deciding support for governments and environmental agencies.

Description: The importance of autonomous in situ chemical sensors for ocean observations has increased drastically over the last decades. Yet, the huge potentials of sensor-based data collection remain underutilized by the scientific and regulatory communities, despite wider than ever usage of sensors. This thesis is part of a growing body of work to extend the usability of sensors and is embedded in the Ocean Best Practice approach, which could improve data quality in ocean observation in general. The here presented Ph.D. thesis covers multiple commercial sensors (LOC from ClearWater Sensors, Southampton, UK and OPUS from TriOS GmbH, Germany) for autonomous, high-resolution and in situ measurements of essential biogeochemical parameters (pH and nitrate) in marine waters. It was motivated by the necessity of improving the data quality of autonomous submersible optical sensors and broadening their utility. To achieve this, sensor deployments in various aquatic environments were conducted. Furthermore, the data obtained via sensors based on the same analytical principle was compared with each other, and with benchtop laboratory devices to assess the accuracy of the measurements. The achievements are associated with the acquisition of accurate and temporally well-resolved real-time data. A more reliable sensor-based data collection and improved deployability promotes a broader usage of autonomous sensors in general. Thus, a financially more sustainable ocean monitoring approach can be achieved, since a broader adaptation of autonomous sensors in research yields a higher cost efficiency.

Description: The harmful algal bloom(HAB)-forming species Alexandrium ostenfeldii produces paralytic shellfish poisoning (PSP) toxins and the lesser known spiroimine shellfish poisoning (SSP) toxins. These toxins primarily belong to macrocyclic imine class, with cyclic imine moiety and macrocyclic nature as their distinct characteristics. By far, A. ostenfeldii is the only species identified to produce two types of cyclic imines—gymnodimines and spirolides. Studies on these toxins produced by different A. ostenfeldii strains revealed high structural diversity. The presence of highly varied structural types of cyclic imines that requires elaborate synthesis pathways implies its underlying function for the producing organism. However, known roles and mode of action (MOA) of cyclic imines are rather limited. That is, other than its “fasting-acting” toxicity and antagonistic activity against of nicotinic acetylcholine receptors, no other MOA of cyclic imines have been identified. Considering the increasing occurrence of HABs and the socio-economic impacts of toxins associated in A. ostenfeldii, it is crucial to elucidate not only the structural diversity of cyclic imines but also their respective modes of action and biological significance of their production. As such, this study aimed to isolate, characterize, and screen the bioactivity of the two types of cyclic imines (i.e., gymnodimines and spirolides) produced by A. ostenfeldii. Two strains of A. ostenfeldii (OKNL 48 and X-LF-19-F10) were mass cultivated to directly obtain purified samples of structurally known gymnodimines (i.e., gymnodimine A (GYM A)) and spirolides (i.e., 13-desmethyl spirolide C (SPX 1)). A total of 345 µg of GYM A and 559 µg of SPX 1 were purified (〉95% purity) from the large-scale microalgal culture. Three other A. ostenfeldii strains (AON 24, NX-56-10 and MX-S-B11) were identified to produce both structurally unknown spirolides. Isolation of the pure novel spirolides were not possible in quantities necessary for NMR structure elucidation work. Thus, mass-spectrometric (MS)-based techniques was sought as an alternative approach for the structural characterization of unknown compounds. Using the technique, this study revealed the presence of nine novel spirolides, eight of which have either a 5:5:6 (C-type spirolides) or 5:6:6 (G-type spirolides) triketal ring configuration. Another novel spirolide putatively belongs to a new spirolide subclass, which has a 6:5:6 triketal ring configuration that is only observed in pinnatoxins, another class of cyclic imines. The initial structural insights by mass spectral techniques demonstrate that structural variability of spirolides is not only limited to the presence or absence of certain functional groups (as observed in other eight novel spirolides) but also the triketal ring system. Moreover, the proposed 6:5:6 triketal ring system in one of the novel spirolides suggests that similar biosynthetic steps are involved in the synthesis of spirolides and pinnatoxins. To gain a better understanding on the potential role of cyclic imines, purified GYM A and SPX 1 were subjected into cell line-based bioassays to identify other MOA of the toxins. Intracellular calcium levels ([Ca]i) measured in rat pheochromocytoma (PC12) cells suggested that both toxins elicited differential effect on acetylcholine receptor (AChRs) subtypes. GYM A and SPX 1 activates nicotinic AChRs (nAChRs) while only GYM A activate muscarinic AChRs (mAChRs). The activation of AChRs and the subsequent influx of calcium ions into the cell illustrates the putative capacity of the toxins to mimic acetylcholine. These observations were possible as a result of determining the response of GYM A or SPX 1 on [Ca]i signaling in PC12 cells. Moreover, preliminary investigations on the effects of GYM A and SPX 1 to AREc32 and Nf-κB-bla THP-1 cell lines indicated that toxins potentially induce adaptive stress response pathways. SPX 1 likely activates both oxidative stress response and inflammation response pathways. GYM A, on the other hand, possibly initiates inflammation response pathways but lacks the capacity to induce oxidative stress response pathway. The ability of the toxins to potentially activate adaptive response pathways indicated that GYM A or SPX 1 might initiate cellular processes that will restore homeostasis suggesting possible medicinal applications of the toxins. Studies on the response of GYM A and SPX 1 to [Ca]i and adaptive stress response pathways provided more understanding on the potential MOA of the toxins. Further knowledge on structural diversity and MOA of cyclic imines could hopefully direct us to determine structure-activity relationship and, to some extent, purpose of the toxins to the producing organism.

Description: Ongoing global climate changes leads to an increased water temperature and a higher probability of extreme events. This thesis focuses on (i) the characterisation of heatwaves and cold-spells in the Kiel Fjord, (ii) using this characterisation for treatment development, (iii) running mesocosm experiments to unravel the importance of frequency, duration, and intensity of environmental stress (i.e., heatwaves, upwelling, and warming) for the impact on the two important species Asterias rubens and Zostera marina, and (iv) the coping mechanisms of these species with (succeeding) environmental stress. Starfish were substantially impacted by heatwaves, with stronger and longer-lasting impacts in amplified and prolonged heatwaves. The impacts reached from 100% mortality (simulated future intensity) to decreased feeding rates, lower growth, and reduced activity (today’s intensity). Upwelling reduced the starfish's activity. However, the succession of extreme events led to an alleviated impact during the second event. Eelgrass was not impacted by short heatwaves or upwelling alone but had less leaves when the heatwave was extended, or a short heatwave was followed by upwelling. The latter combination of stressors also reduced the number of eelgrass shoots. When exposed to long-term warming, aboveground and belowground biomass of non-heat-selected eelgrass was strongly reduced. However, eelgrass individuals from a potentially heat-selected population grew more than those from a non-heat-selected population. Overall, this thesis highlights that extreme events are important drivers of temperate benthic ecosystems but that their impact depends on the nature of the event, their succession, duration, and intensity. Yet, species may have the potential to cope with recurring stress events via an ecological memory or via heat-selection in situ.