Kröncke, Ingrid
Loading...
Preferred name
Kröncke, Ingrid
Official Name
Kröncke, Ingrid
6 results
Now showing 1 - 6 of 6
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, 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.doctoral thesis428 308 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Recruitment dynamics of North Sea macrozoobenthos in intertidal soft bottoms: larval availability, settlement and dispersal(2003-11-04); ; ; This thesis investigates how larval supply, larval settlement and secondary dispersal affected recruitment and recovery of macrozoobenthos living in an intertidal sand flat located in the German Wadden Sea. The temporal availability of meroplanktonic bivalve larvae was related to the timing of sea water temperature increase and/or the timing and magnitude of phytoplankton blooms. Larval settlement of the polychaete Lanice conchilega occurred almost exclusively at exposed sites within the adult habitat and was dependend upon the density of the adults. Model simulations revealed that dense L. conchilega patches develop only in areas of high near-bottom flows. In contrast, bivalve larvae settled mainly in sheltered habitats. Both polychaetes and bivalves undergo phases of postlarval dispersal which rapidly changed the spatial patterns generated by larval settlement. In-situ staining experiments showed that secondary dispersal is strongly size/age dependent. The recovery of two macrobenthic assemblages following the severe winter was rapid (<1 year) and influenced by 1) species life histories, 2) habitat conditions, and 3) biotic interactions, namely facilitation. The temporal course of recolonisation was mainly determined by the availability of settling stages (larvae and postlarvae). This thesis elucidates that both pre- and post-settlement processes contribute to the recruitment and recolonisation of macrozoobenthic communities. In dynamic systems, flexibility of life histories, high mobility of benthic life stages and the existence of functionally distinct life stages provide multiple paths to population maintenance and a high resilience. It is highlighted that at the end tides and currents are the decisive processes because they set the boundary conditions to which organisms respond and mediate the function of many processes such as larval drift, larval settlement and secondary dispersal.doctoral thesis261 155 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Physiochemical responses of an asterinid starfish (Echinodermata: Asteroidea) to global ocean change(2024-11-12); ; ; The continuous increase in greenhouse gas (GHG) emissions, especially carbon dioxide (CO2), since the beginning of global industrialization has resulted in significant alterations in seawater physicochemical properties, particularly elevated seawater temperatures (ocean warming, OW) and ocean acidification (OA). These changes have wide-ranging consequences for marine organisms, affecting their biological functions and ecological roles. The combined effects of OW and OA may amplify adverse outcomes compared to individual stressors due to the complex reorganization of cellular mechanisms and molecular pathways, which subsequently appear in behavioral modifications. However, organismal reactions and thresholds to these stressors are variable, which might differ within organism ontogeny or among taxa, making predictions challenging. Therefore, increasing research has been performed to better understand the potential mechanisms underlying the ability of marine organisms to alleviate the effects of environmental change, mainly due to OW and OA. Thus, employing multiple bioindicators, specifically keystone species such as starfish, to evaluate the impacts of OW and OA offers a comprehensive approach to examining their effects not simply on the organism concerned but also on the broader ecosystem. The presented studies in this thesis aim to contribute to the understanding the role of physiochemistry and trade-offs on marine ectotherms, particularly asterinid starfish, in coping with environmental stress. For this purpose, mineralogic, metabolic, behavioral, lipidomics, and enzymatic activity approaches are used. The research summarized in this thesis provides the first investigation of the effects of global ocean change on biomineralization and physiological traits through long-term experiments using asterinid starfish species, Aquilonastra yairi, distributed in tropical to subtropical regions (across the Mediterranean Sea, Red Sea, and Gulf of Suez). The starfish were exposed to two temperature levels (27 °C and 32 °C) crossed with three pCO2 regimes (455 µatm, 1052 µatm, and 2066 µatm), representing factorial combinations of ambient conditions and future levels of CO2 and temperature change according to the IPCC-Representative Concentration Pathways (RCPs) 8.5 greenhouse gas emission scenario for the year 2100. The present work revealed that asterinid starfish demonstrate high stressor tolerance and resilience to increased temperature and pCO2 through adaptive adjustments in physiological functions or behavioral activities, suggesting high homeostatic capacities and the ability to regulate physiochemical response to maintain survival, fitness, and metabolic biosynthesis under chronic conditions. The temperature was the predominant factor, exerting a significant effect on the magnitude and frequency of the affected physiological-related processes; however, concurrent exposure to OA and OW stress produced synergistic effects on some of the starfish physiology-related responses tested. While decreased pH negatively affects starfish calcification performance, the increased temperature potentially mitigates these effects. However, increased temperature might also lead to more magnesium (Mg2+) incorporation into the calcite lattice, potentially compromising the starfish skeleton. Furthermore, it was revealed that starfish can preserve lipid-associated biochemistry (FAs) under elevated temperature and pCO2, which potentially provides molecular instruments to cope with future OA and OW scenarios. However, combined OA and OW significantly affected Ca-ATPase and Mg-ATPase enzyme activities, which are recognized to play an important role in the biomineralization pathway, raising concerns about potential susceptibilities in skeletal development and preservation. Investigating the complex impacts of global ocean change on marine organisms requires a comprehensive research approach that encompasses diverse biological, chemical, and physical traits. Understanding the physiological and chemical responses of bioindicator species, e.g., asterinid starfish, to combined stressors OW and OA is important to comprehend the relationships and interactions between biological processes and abiotic environmental conditions, which in turn essential for accurately predicting their resilience, ecological implication, and broader ecosystem dynamics. At the ecosystem scale, this study significantly contributes to the ongoing knowledge for future studies of the impact of climate change on coral reef-associated invertebrates. Specifically, this finding is beneficial for the conservation of coral reef ecosystems under future ocean conditions.doctoral thesis190 162 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Hydro-acoustic characterization of trawl marks in the German Exclusive Economic Zone (North Sea) as a function of sediment properties(2023-09-11); ; ; Marine habitats are increasingly impacted by human activities. Bottom trawling, in particular, contributes to this impact by causing sediment displacement and disrupting the habitat of benthic species. An indicator of sediment reworking caused by bottom trawling on the seafloor is the presence of trawl marks. These elongated furrows are left behind by trawl nets in the sediment and can be observed in hydroacoustic data such as side-scan sonar images. Such trawl marks are known from various marine habitats, and their significance for sedimentation - for example, as an indication of increased erosion - has been the subject of extensive research. However, detailed investigations of such marks have been scarce for the North Sea region within the German Exclusive Economic Zone (EEZ). The present dissertation includes a comprehensive mapping of trawl marks based on approximately 4800 km² of side-scan sonar backscatter data collected in the North Sea part of the German Exclusive Economic Zone (EEZ). Detailed analysis of the trawl marks revealed seasonal variations in their spatial density and allowed for estimates of their persistence. Additionally, sediment strength data provided evidence of the physical impact of trawl nets on the seafloor and reflecting surface sediment reworking. The extensive side-scan sonar dataset also facilitated the development of an approach for automated trawl mark detection.doctoral thesis189 134 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Habitat dynamics in response to constructional impacts (JadeWeserPort) a biological approach(2016-08-03); ; ; During the construction of a deep-water port (JadeWeserPort), bathymetry, sediment distribution, and macrofauna community structure were studied in the Inner Jade, a tidal channel located in the southern North Sea. The relationships between macrofauna community structure and natural as well as anthropogenic environmental variables were investigated in this very heterogeneous study area. The manual expert hydroacoustic classification of the backscatter image derived by side scan sonar was successful to detect the different dredging activities and the natural bedforms in the undisturbed areas. The sediment distribution was very patchy and no significant congruence with the hydroacoustic classification could be identified. In contrast, low, but significant relationships between the hydroacoustic classification and the macrofauna community structure as well as the sediment distribution and the macrofauna communities were found. The most important impact on the spatial community structure was the number of days after the last dredging/dumping activity for the JadeWeserPort (JWP), followed by the sediment characteristics explained by grey values of the backscatter image. This study stresses the problems of benthic habitat mapping in such a heterogeneous area. In order to assess the effects of physical disturbance by dredging activities, macrofaunal community compositions between 2002 (before the construction work had begun) and 2010 (during the final construction phase) were compared. The sand extraction for land reclamation and the redirection of the navigation channel changed the bathymetry markedly. While the old navigation channel in the centre of the study area remained mud dominated, a general increase in coarse sediments was detected in 2010. The dynamic nature of the study area in combination with the direct and indirect effects of dredging increased the bathymetric heterogeneity (measured by singlebeam (2002) and multibeam (2010) echo-sounder). In 2010, the macrofauna community structure roughly resembled the different categories of dredging activities. A general increase in macrofaunal abundance and taxa number was observed in 2010, with the exception of the recently dredged area. The structure of the macrofauna community during the port construction phase seemed to be determined by secondary dispersal of the dominant taxa and recolonisation by highly mobile and opportunistic species. The effects of the presence of two adult bivalve species with different feeding modes on the post-settlement dispersal of their juveniles were examined in a flume experiment.doctoral thesis366 278 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Macrozoobenthic response to fishery: trophic interactions in highly dynamic coastal ecosystems(2007-11-14); ; ; This thesis aims at achieving deeper insights into the ecological functioning of German Bight benthos, i.e. ecosystem trophic properties that might explain resistance of the system in the light of decades of frequent bottom trawling, and recovery patterns of the benthic system during 14 months of trawling cessation.(i) Stable isotope ratios served as an indicator for species trophic elevation, i.e. the relative distance of a species to the primary food source within the food web hierarchy. Community trophic complexity and species trophic niche width were determined by means of interspecific and intraspecific variability of trophic elevation. Trophic significance, i.e. a metabolism scaled abundance, served as an indicator of trophic flow through particular populations.(ii) A new two-dimensional approach to trophic complexity (horizontal and vertical diversity) was developed. It was applied to the German Bight ecosystem, but concurrently provides a robust and standardised tool for the comparison of species and ecosystem trophic properties.(iii) The macrozoobenthic response to trawling cessation was investigated over the course of 14 months by two approaches: firstly, multivariate community analyses using numerical measures which follow changes at different system levels: the community level, the level of compartments (e.g. feeding guilds) and the species level; secondly community and species trophic properties, i.e. trophic elevation and trophic significance. For the first time, this approach identified significant changes due to trawling cessation on a short time-scale within a highly dynamic coastal ecosystem.The synthesis of all results provides a detailed picture of trophic functioning of the German Bight benthos: (a) Most species are trophic generalists, i.e. they are connected by many and mainly 'weak' trophic links. (b) Trophic redundancy is comparatively high, i.e. the loss of one species may be compensated functionally by one or more other species. (c) In terms of size distribution, the system is characterised by small-sized organisms with corresponding high turnover rates. These particular food-web properties correspond to high system resistance, i.e. the current state can be maintained despite the severe impact of continuing bottom trawling.doctoral thesis569 237