Bischof, Kai
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Bischof, Kai
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Item-typ:Veröffentlichung, Range expansion mechanisms of the invasive kelp Undaria pinnatifida(2017-06-13); ; ; Species invasions in marine habitats have dramatically increased in the last decades. This thesis revealed characteristics of the invasive kelp Undaria pinnatifida that support its invasive potential along various phases of the invasion process. Experiments, including morphological, physiological and biochemical analyses, explored traits of different life history stages. The kelp displayed broad physiological tolerance to the tested abiotic factors (desiccation, temperature, salinity). Based on its capability to survive extended periods of air exposure, overland transport is proposed as an invasion vector for U. pinnatifida. With regard to elevated temperatures the invader outperformed native kelps, indicating a competitive advantage in a warming ocean. Observations of simultaneously developing gametophytes revealed the occurrence of inter-specific interactions at microscopic stages. Interactions of U. pinnatifida and Macrocystis pyrifera resulted in an enhancement of the invader's performance.Dissertation366 158 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Polar Night eco-physiology, and eco-evolutionary dynamics of the kelp Saccharina latissima(2023-10-13); ; ; For primary producers, the suitability of the High Arctic (~ 80 °N) as habitat depends on their capacity to survive the long-term absence of light during the Polar Night. During the Climate Crisis, it now strongly depends on their capacity to adapt to the combined threat of rise in temperature and prolonged darkness during the Polar Night. This thesis addresses, mainly for the kelp Saccharina latissima, eco-physiological as well as transcriptomic aspects of rising temperature during Polar Night. For a more holistic impression of the adaptive capacity, it further provides a comparative epigenetic assessment of the nuclear and chloroplast genome regarding dynamics of eco-evolution in this kelp. Results obtained during this dissertation provide a solid interdisciplinary data complex on two topics where data have been severely missing for (High Arctic) kelp. They have already been incorporated into a scientific book (Berge et al 2020, see references within this work), and have laid the foundation for a completely new branch of research on kelp (priming). In conclusion, this dissertation contributes important knowledge gains for a more holistic understanding of (High Arctic) eco-evolutionary processes during the current biodiversity crisis in the wake of this Climate Crisis, and a possible counteraction method.Dissertation204 197 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Macroalgal Performance and Competition under Elevated CO2(2012-09-04); ; ; Since the industrial revolution, atmospheric carbon dioxide (CO2) concentrations have been increasing, and the surface waters of the global oceans have absorbed 30% of the anthropogenic CO2 released into the atmosphere. A higher CO2 concentration in surface ocean waters shifts the carbon chemistry, resulting in higher concentrations of bicarbonate ions (HCO3-) and protons (H ) and lower concentrations of carbonate ions (CO32-). Such a shift in ocean carbon chemistry decreases the pH and the saturation state of the seawater with respect to CO32- thereby making the precipitation of CaCO3 less kinetically favorable. These changes in ocean chemistry termed ocean acidification) are expected to have negative impacts on marine calcifying organisms, which deposit CaCO3 in the form of aragonite, calcite and high-magnesium calcite into their shells and skeletons. Because calcifying marine primary producers are very important to the carbon cycle and for rocky shore habitat structure and stability, investigating how they will respond to future oceanic CO2 levels is a relevant and important topic of research. Therefore, two calcifying marine macroalgae were chosen as the central organisms for investigation in this thesis. I investigated the physiological responses of the temperate calcifying coralline rhodophyte alga Corallina officinalis (L.) and the tropical calcifying chlorophyte alga Halimeda opuntia (L.) J. V. Lamouroux to elevated CO2 concentrations which are expected to occur by the end of this century. Furthermore, the effect of elevated CO2 on the competitive interactions between these two calcifiers and their noncalcifying counterparts was investigated in order to predict how macroalgal communities will respond to future surface ocean CO2 levels in both temperate and tropical environments. Because CO2 concentrations are increasing in surface ocean in parallel with other abiotic stressors, I also chose to investigate the response of H. opuntia to the combined effect of elevated CO2 and inorganic nutrients, which replicates a likely scenario for the condition of some eutrophied tropical coral reefs at the end of this century. The studies carried out during this thesis revealed that there are differences in the physiological responses of calcifying macroalgae to elevated CO2, but similar patterns of competitive interactions between calcifiers and noncalcifiers occur under elevated CO2 regardless of species and latitude. I found that the temperate coralline alga C. officinalis was highly sensitive to elevated CO2, as shown by lower growth and 3 photosynthetic rates and less calcified cell walls than under normal conditions. On the other hand, the tropical calcifying chlorophyte alga H. opuntia was only moderately sensitive to elevated CO2 concentrations, as this species had lower growth rates but maintained normal calcification rates and increased electron transport rates. Enzyme activity (external carbonic anhydrase and in situ nitrate reductase) in both species was affected by CO2 indicating that external carbonic anhydrase plays an important role in calcification by regulating the speciation of inorganic carbon, and that nitrogen assimilation in these species is affected by elevated CO2. The effect of CO2 on energy balance in these two species is also discussed. The different calcification mechanisms utilized by these two species is likely to account for some of the observed differences in physiological responses, and is discussed in detail below. While these two species showed different susceptibilities to elevated CO2 in isolation, they both showed similar sensitivity to overgrowth and outcompetition by noncalcifying algae when grown with their natural communities under elevated CO2 conditions. This trend was amplified under conditions of inorganic nutrients. The results of this thesis indicate that calcifying macroalgae show differences in their susceptibility to ocean acidification, but regardless of their sensitivity in isolation, both temperate and tropical species are likely to be outcompeted by noncalcifying macroalgae under elevated CO2 conditions. Tropical systems are especially susceptible to a shift in community composition (from calcifier- to noncalcifier-dominated) when eutrophication and ocean acidification occur simultaneously.Dissertation665 465 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The Dark Side of Polar Day - The influence of coastal run-off on Arctic kelp communities(2024-09-20); ; ; ; Ecosystem engineering kelp forests are subject to many rapid environmental changes in the Arctic. Since the 1980s, the rate of sea surface temperature rise is far beyond the global average. Consequently, glacial and permafrost melt are accelerating, leading to extensive run-off plumes covering fjords. Run-off plumes alter many water column parameters: e.g., high concentrations of suspended particles are changing the photosynthetically active radiation (PAR); terrestrial and lithogenic material alter the macro- and micronutrient concentrations. To be able to maintain a stable population, kelps have to acclimatise to the changing environment. The overarching aim of my doctoral thesis is to assess what defines the boundaries of the realised niche of Arctic kelp forests. In two in-situ monitoring studies, I found high intraspecific variability in the biochemical composition of different Arctic kelp populations, being conditioned by their local environment along the west coast of Svalbard. Hence, performance curves must not be considered static and experimental results have to be extrapolated with care. Investigating the in-situ effect of run-off on kelp holobiont functioning in a high spatial resolution, I additionally found run-off to change the content of (harmful) elements in kelps. This led to changes of the ecosystem services of kelp forests, such as their nutritious value for grazers, or the element cycling of the ecosystem. In three experimental studies, I found that the effect of temperature on kelps is highly interactive with the prevailing PAR availabilities. High-PAR availability caused drastic physiological stress, especially when interacting with cold temperatures, which currently restricts L. hyperborea to expand to higher latitudes. Reduced irradiance resulted in a shift of the kelps’ realised niche and a local loss of habitat for cold-temperate kelps in the Arctic. Concluding, climate change induced Arctic run-off, and especially varying PAR availability, has drastic consequences on the performance of kelps, with the potential to limit Arctic kelp distribution. A shift of the kelps’ distribution has cascading ecological and economic consequences.Dissertation217 168 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The influence of current velocity, tidal height and the lugworm Arenicola marina on two species of seagrass, Zostera marina L. and Z. noltii Hornemann(2008-06-23); ; ; For this doctorate study several experiments with seagrasses were planned and conducted on the German North Sea island Sylt from 2002 till 2004. The results show that seedlings from both seagrass species grew better at weaker current velocities than at stronger velocities, with Zostera noltii being able to withstand higher velocities longer than Z. marina. The lugworm Arenicola marina negatively influenced Z. noltii, but did not influence Z. marina. The combination of higher current velocities and lugworm presence was particularly bad for Z. noltii. Both seagrass species grew better in the upper eulittoral compared with the lower eulittoral. In the donor population, Z. marina seedlings emerged 3-4 weeks earlier at the sediment surface than Z. noltii seedlings. Despite this Z. noltii seedlings had nearly the same shoot length by late June 2004. Neither seagrass species transferred carbon or nitrogen from the leaves to the roots/rhizomes with the onset of winter. The phosphate concentration in the porewater of the seagrass meadows might be limiting seagrass growth but ammonium and silicate concentrations are not limiting.Dissertation269 164 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Light acclimation in intertidal seagrass : spatial and diurnal variations and the role of suspended sediments(2016-10-04); ; ; Seagrasses are the prevailing macrophytes along soft sediment coasts. One of the most important anthropogenic stressors for benthic macrophytes is increased suspended sediment loads and the attenuation of underwater light. Along many temperate coasts seagrasses occur predominantly in the intertidal but knowledge on the photophysiology of intertidal seagrasses is scarce. Studies focussing on the photoecophysiology of intertidal seagrasses are therefore urgently needed and the aim of this thesis was to fill this gap and provide some in-depth information on light acclimation mechanisms in intertidal seagrasses over diurnal and spatial scales. In a second step the impacts of suspended sediments on the underwater light regime and thus seagrass photosynthesis were examined. The first study assessed light adaptive strategies in a comparative analysis of the congeneric seagrass species Zostera muelleri and Zostera marina at two case study areas in New Zealand and Germany. The results showed marked fluctuations of photophysiology (maximum and effective quantum yield, non-photochemical quenching, cycling of xanthophyll cycle (XC) pigments) over daily and tidal cycles with a full xanthophyll cycle at both locations. At the New Zealand site we also observed significantly larger XC-pigment pool sizes in seagrass leaves sampled in a week when low tide coincided with noon. This very dynamic adjustment of xanthophyll pool sizes has not been previously reported for intertidal seagrasses and highlights their ability to adjust to strongly fluctuating irradiances in the intertidal. The high physiological plasticity of Zostera in light-saturated environments was also illustrated by the second study, which evaluated spatial differences in seagrass cover related to environmental conditions (light, temperature, sediment grain size distribution, and porewater nutrients) and differences in seagrass photosynthetic pigment composition and morphometry (above and below ground biomass, shoot length and leaf width, and percentage cover) at four sites in the meso-tidal estuarine lagoon of Tauranga Harbour, North Island, New Zealand. There were marked differences in pigment content and composition (as a marker of physiological plasticity), seagrass metrics as well as in environmental conditions. Our findings emphasize the high physiological plasticity and revealed also morphological plasticity of Zostera muelleri. Both studies underlined the general high light adaptation of intertidal seagrasses and their ability to thrive in fluctuating light environments. However, strong reductions in light conditions, e.g., through increased sediment loads entering coastal systems, may negatively affect seagrasses. Hence, the third study elucidated to what extent different sediment types (marine vs terrestrial) in different concentrations changed the underwater light regime in terms of overall photosynthetically active radiation (PAR) and the attenuation coefficient of downward irradiance of PAR (Kd) and quality (spectral composition). In a tank experiment the influence of different sediment types and concentrations were determined. In situ measurements of light quality and quantity, and suspended sediments (total suspended solids, TSS) at 12 sites in and outside of Tauranga Harbour, demonstrated that the lowest Kd and TSS values were found outside, and the highest within the harbour. Different scenarios for sediment loads, how they influence the underwater light regime and the potential for the vertical distribution of seagrass meadows are discussed. Relatively low Kd values of ~1 (as observed e.g., at the inner site of the lagoon) may already lead to maximum colonization depths of less than ~2 m, i.e., a limitation of seagrasses to intertidal habitats. This shows that current sediment loads and the resulting light conditions impair the growth of seagrasses beyond the intertidal at most sites. The (re)colonization of subtidal habitats may require significantly lower sediment loads entering the coastal zone. Therefore, authorities should consider an effective management on land and at the coast to keep anthropogenic sediment inputs at a minimum.Dissertation431 174 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The ecology of natural and artificial hard substrata in marine coastal environments: substrate characteristics as facilitator of settlement and community stability(2021-10-15); ; ; Natural hard bottom ecosystems worldwide provide unique ecological functions and services within their respective environments. They protect coastlines by dampening large waves, reducing flooding, and preventing erosion. They act as nursery grounds for the associated fauna and play an important role in benthic-pelagic coupling, nutrient cycling and water purification. The rapid growth of the coastal infrastructure due to an ever-increasing population in coastal regions, as well as the growing challenge of global climate change (sea level rise, ocean acidification), are a serious threat to these ecosystems. The management focus on supporting local biodiversity in order to maintain natural ecosystem functioning and services is essential to safeguard a sustainable coastal development. Hence, while there is a strong need in protecting the still remaining natural hard bottom ecosystems, there is also an upcoming demand for reconsidering the way new coastal infrastructure is to be built. Engineering solutions need to focus on the objective to maintain local species richness, while also reducing the demand for natural resources in the production process of new building materials. The main objective of this doctoral project was to define drivers, which influence benthic community establishment in marine natural and artificial hard bottom systems. The influence of different physical environmental conditions and substrate characteristics in the settlement processes and community establishment was evaluated. Risks of invasion by neobiota in natural and artificial structures and options to implement natural ecosystem services in artificial environments as protection against invasion were discussed. The first part of this dissertation focusses on habitat characteristics of natural hard bottom systems of the southern North Sea, Germany. The southern North Sea is a marine environment with relatively low proportion of natural hard bottom ecosystems. Observation and monitoring of these protected grounds is often difficult due to the heterogeneous habitats and overall low visibility. Chapter 2 shows how video sampling methods in combination with environmental distribution maps on sediments, currents, and depth can help to model the status quo of biotic and abiotic conditions within a German nature conservation area, the “Helgoländer Steingrund” (HSG; 54°14.00N and 8°03.00W). Within this study, a new approach using species distribution models was tested on presence/absence data of nine benthic species (Echinus esculentus, Metridium senile, Cancer pagurus, Phymatolithon spp., Axinella polypoides, Homarus gammarus, Flustra foliacea, Alcyonidium diaphanum, Alcyonium digitatum). The species distribution models revealed good evaluation measures (true skill statistic >0.7; area under the receiver operation characteristic curve >0.90), implying that the model shows a good predictive performance. The outcome of this study is a clear recommendation on SDM application in further environmental monitoring programs on the HSG and other protected hard ground areas. Chapter 3 compares different hydroacoustic and hydrodynamic measurement tools to improve the assessments of the environmental conditions in the study area. Sonar systems, underwater videos, and bottom samples were used for mapping and classifying the abiotic and biotic components of the habitat. Based on acoustic backscatter data three main seabed types (sand, gravel, and hard substrate) were identified. The additional information from underwater videos and sediment samples lead to an expansion to six seabed types with different abiotic and biotic components. The flanks of the ridge of the HSG and their transition to the surrounding soft-ground areas were characterized by a distinct dominance of the bryozoa Flustra foliacea and Alcyonidium diaphanum. Acoustic Doppler Current Profiler data showed a uniform flow pattern across the ridge, and even resolved the local variability of current patterns, dependent of the tidal stage and bottom relief. Flow patterns are likely responsible for the zonation of the two benthic species. The second part of this dissertation focusses on habitat characteristics and succession on artificial substrates and environments. Those were in the focus of one-year succession studies presented in chapter 4 and chapter 5. The experiments described the establishment of benthic communities on concrete cubes (15 x 15 x 15 cm) made from five different concrete mixtures. The concrete mixtures contained various cements (Portland cement and blast furnace cements) and aggregates (sand, gravel, iron ore and blast furnace slag). Depending on their mixture, natural resources were saved, and CO2-emissions were reduced. This makes the materials “environmentally friendly”. All cubes were deployed in April 2017. After 12 months, they were examined regarding species composition and coverage, followed by statistical analysis (PERMANOVA, SIMPER, DIVERSE). One succession study was carried out in a natural hard bottom ecosystem near the island of Helgoland (chapter 4). The second study was conducted at the JadeWeserPort, Wilhelmshaven, as an example of a recently erected artificial habitat with high anthropogenic impact (chapter 5). Chapter 4 showed differences in settlement communities for different surface orientation of the cubes. Significant differences in settlement communities of the Front/Back side were present depending on the used concrete mixtures. Chapter 5 indicated marked differences in settled communities at the Port site compared to the natural environments of Helgoland. At the Port site community composition did not differ between the concrete mixtures. However, surface orientation of the cubes again revealed significant differences in species abundances and compositions. Cubes hold more neobiota in the Port site than in natural hard ground environments. Recommendations for the usage of “environmentally friendly” produced concrete mixtures are given. Regarding new coastal constructions, a sustainable production process of the required building materials should always be considered. As long as no significant difference in succession patterns and establishment of benthic communities between the “environmentally friendly” produced concrete mixtures and those that are commonly provided is present, “environmentally friendly” produced mixtures should be used. Anyhow, this is not sufficient to help maintaining ecosystem services under future scenarios of climate change. On the one hand, a protection of natural hard bottom systems is essential to maintain natural ecosystem service and functioning. On the other hand, the potential of artificial structures in restoring ecosystem services should not be underestimated. Artificial structures, if they fulfill certain criteria, as the use of environmentally friendly produced materials and combine those for instance with an enhanced habitat complexity, can, to certain extent compensate for natural habitat losses. If they host high biodiversity of native species, they can also be used to protect natural coasts from invasion by neobiota.Dissertation425 297 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Interactive abiotic stress effects on Arctic marine macroalgae- Physiological responses of adult sporophytes(2009-04-29); ; ; In Arctic coastal ecosystems, marine macroalgae are exposed to a multitude of abiotic and biotic stressful conditions, including naturally seasonal variations and additionally potential effects of climate changes. Although the different abiotic variables are acting in combination and interdependently in the natural environment, the responses of macroalgae to interactive effects of multiple abiotic stressors are relatively unknown. UV-induced effects and growth temperatures are well studied on different macroalgal species, but mainly in single-factor experiments. Accordingly, the present thesis aims to detect interactive effects of combined abiotic environmental factors on Arctic marine macroalgae from the Kongsfjord (Spitsbergen) for a better understanding of their stress physiology and to estimate potential ecological implications. The study focused on physiological responses of different macroalgal species exposed to impacts of temperature stress in combination with radiation as well as salinity conditions.Dissertation323 140 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Photosynthesis and photoinhibition at low temperatures: physiological responses of Antarctic rhodophytes(2010-03-16); ; ; The environment of Antarctica represents one of the most challenging and harshest ecosystems, characterized by very low temperatures and a strong seasonality in light availability. Due to the abiotic conditions, inhabiting organisms are highly adapted to their habitat and possess the ability to cope flexibly with changing environmental factors. In the context of global climate change, the Antarctic and especially the Antarctic Peninsula undergo the most rapid and significantly changing regions worldwide. The combination of low temperatures and high light intensities are challenging conditions for photosynthetic organisms, as low temperatures reduce for instance enzymatic processes and the turn-over of the D1 centre protein of photosystem II. This protein plays a crucial role in photosynthetic function.Low water temperatures also decrease membrane fluidity, resulting in an impairment of transfer processes for instance through the thylakoid membrane of chloroplasts. In addition, photosynthetic activity is particularly sensitive to low temperatures, as enzymatic secondary reactions are strictly temperature-dependent, while primary reactions are not. The present thesis investigated the physiological performance, the acclimation potential and tolerance limits of the endemic Antarctic rhodophyte Palmaria decipiens. In various experiments conducted under laboratory and field conditions, the alga was exposed to changing light and temperature levels. It was hypothesized that in particular the combination of photosynthetically active radiation (PAR, 400-700 nm) and low temperatures lead to stress responses in the organism. To estimate the responses of P. decipiens, the alga was exposed over different periods of time to natural and artificial radiation. The macroalgae investigated in the present study revealed a relatively high acclimation potential within their species-specific tolerance ranges. Obviously, this tolerance is limited and particularly rapid and pronounced changes can impact seaweeds negatively. To obtain realistic predictions in a more ecological context, investigations should involve interactive effects of the abiotic and biotic conditions. In summary, this study demonstrates that Antarctic rhodophytes are very well adapted to their environment and are, in spite of this, still able to acclimate and cope with certain changes in the abiotic conditions. The results obtained during the present study also indicate that the combined effects of environmental conditions is an important issue that has to be considered when adressing ecological questions.Dissertation383 219 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Impact of mangroves and an agriculture-dominated hinterland on the carbon and nutrient biogeochemistry in the Segara Anakan Lagoon, Java, Indonesia.(2011-04-15); ; ; The Segara Anakan Lagoon on Java, Indonesia, is mainly threatened by sedimentation and mangrove tree logging. The lagoon size decreased by >50% since the 1970´s due to high sedimentation loads from the Citanduy River and therefore the agriculture-dominated hinterland. The nutrient concentrations were significantly higher during the rainy season and mainly derived from the Citanduy River. Also mangrove leaves leached high amounts of nutrients into the system. However, the nutrient concentrations were low to moderate on a global scale. Nutrient sinks in the SAL were outwelling, assimilation by mangrove and shrub species, consumption by microbes and phytoplankton. A further shift from true mangrove tree species to shrub species due to logging can alter the carbon and nutrient inventory in the lagoon. Shrub species leached significantly more nutrients than true mangrove tree species which might accelerate the nutrient turnover rates in the lagoon and therefore affect the whole food web.Dissertation321 310