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  • 2015-2019  (249)
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  • 1
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (79 Seiten = 8 MB) , Illustrationen, Graphen, Karten
    Edition: 2021
    Language: English
    Note: Zusammenfassung in deutscher und englischer Sprache
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  • 2
    Publication Date: 2019-10-28
    Description: In the naturally acidified Comau Fjord (Chile), high densities of the cosmopolitan cold-water coral (CWC) Desmophyllum dianthus are found at or below aragonite saturation (Ωar ≤ 1). However, it is not known so far if seasonal changes in Ωar lead to seasonal differences in calcification rates and the corals’ ability to up-regulate the pH in the calcifying fluid (pHcf). In the present study, corals were sampled along both horizontal and vertical pH gradients (pHT = 7.6-7.9, Ωar = 0.76-1.45) in Comau Fjord. We compared D. dianthus’ calcification rates (buoyant weight technique) with the physico-chemical conditions in the water column (T, Ωar) in austral summer 2016/2017 and winter 2017. In order to determine the biological pHcf up-regulation of D. dianthus, the skeletal boron isotopic composition (δ11B) was measured in the upper part of the calyx between the septa, using a UV femtosecond laser ablation system connected to a multicollector inductively coupled plasma mass spectrometer (LA-MC-ICP-MS). Higher growth rates of D. dianthus were found in summer than in winter. Surprisingly, growth of D. dianthus was highest in undersaturated waters in both seasons (Ωar = 0.76 and 0.84) and cross-transplanted specimens were able to acclimatise to Ωar 〈 1. Therefore, the present study shows that Ωar alone is a poor predictor of D. dianthus growth. Skeletal analyses show a complex relationship between δ11B and the structure of the coral skeletons. δ11B measurements were highly variable, which may be attributed to the high calcification rates in the upper part of the coral calyx. Therefore, high resolution analyses of the skeletal composition and micro-structure will be conducted along the entire longitudinal section of D. dianthus skeletons using Raman microscopy and scanning electron microscopy (SEM). In addition, δ11B will be measured in different skeletal parts and compared to skeletal structure analyses for a reliable reconstruction of seawater pH at high temporal resolution using skeletons of D. dianthus grown under laboratory and field conditions (Comau Fjord, Chile).
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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  • 3
    Publication Date: 2018-07-03
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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  • 4
    Publication Date: 2022-01-31
    Description: CO2-induced ocean acidification and associated decrease of seawater carbonate saturation state contributed to multiple environmental crises in Earth’s history, and currently poses a major threat for marine calcifying organisms. Owing to their high abundance and good preservation in the Phanerozoic geological record, brachiopods present an advantageous taxon of marine calcifiers for palaeo-proxy applications as well as studies on biological mechanism to cope with environmental change. To investigate the geochemical and physiological responses of brachiopods to prolonged low-pH conditions we cultured Magellania venosa, Terebratella dorsata and Pajaudina atlantica under controlled experimental settings over a period of more than two years. Our experiments demonstrate that brachiopods form their calcite shells under strong biological control, which enables them to survive and grow under low-pH conditions and even in seawater strongly undersaturated with respect to calcite (pH = 7.35, Ωcal = 0.6). Using boron isotope (δ11B) systematics including MC-ICP-MS as well as SIMS analyses, validated against in vivo microelectrode measurements, we show that this resilience is achieved by strict regulation of the calcifying fluid pH between the epithelial mantle and the shell. We provide a culture-based δ11B−pH calibration, which as a result of the internal pH regulatory mechanisms deviates from the inorganic borate ion to pH relationship, but confirms a clear yet subtle pH dependency for brachiopods. At a micro-scale level, the incorporation of 11B appears to be principally driven by a physiological gradient across the shell, where the δ11B values of the innermost calcite record the internal calcifying fluid pH while the composition of the outermost layers is also influenced by seawater pH. These findings are of consequence to studies on biomineralisation processes, physiological adaptations as well as past climate reconstructions.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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  • 5
    Publication Date: 2022-01-31
    Description: The fibrous calcite layer of modern brachiopod shells is a hybrid composite material and forms a substantial part of the hard tissue. We investigated how cells of the outer mantle epithelium (OME) secrete calcite material and generate the characteristic fibre morphology and composite microstructure of the shell. We employed AFM, FE-SEM, and TEM imaging of embedded/etched, chemically fixed/decalcified and high-pressure frozen/freeze substituted samples. Calcite fibres are secreted by outer mantle epithelium (OME) cells. Biometric analysis of TEM micrographs indicates that about 50% of these cells are attached via hemidesmosomes to an extracellular organic membrane present at the proximal, convex surface of the fibres. At these sites, mineral secretion is not active. Instead, ion transport from OME cells to developing fibres occurs at regions of closest contact between cells and fibres, however only at sites where the extracellular membrane at the proximal fibre surface is not developed yet. Fibre formation requires the cooperation of several adjacent OME cells. It is a spatially and temporally changing process comprising of detachment of OME cells from the extracellular organic membrane, mineral secretion at detachment sites, termination of secretion with formation of the extracellular organic membrane, and attachment of cells via hemidesmosomes to this membrane.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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  • 6
    Publication Date: 2023-01-31
    Description: Throughout the last few decades and in the near future CO2–induced ocean acidification is potentially a big threat to marine calcite-shelled animals (e.g., brachiopods, bivalves, corals and gastropods). Despite the great number of studies focusing on the effects of acidification on shell growth, metabolism, shell dissolution and shell repair, the consequences on biomineral formation remain poorly understood, and only few studies addressed contemporarily the impact of acidification on shell microstructure and geochemistry. In this study, a detailed microstructure and stable isotope geochemistry investigation was performed on nine adult brachiopod specimens of Magellania venosa (Dixon, 1789), grown in the natural environment as well as in controlled culturing experiments at different pH conditions (ranging 7.35 to 8.15±0.05) over different time intervals (214 to 335 days). Details of shell microstructural features, such as thickness of the primary layer, density and size of endopunctae and morphology of the basic structural unit of the secondary layer were analysed using scanning electron microscopy (SEM). Stable isotope compositions (δ13C and δ18O) were tested from the secondary shell layer along shell ontogenetic increments in both dorsal and ventral valves. Based on our comprehensive dataset, we observed that, under low pH conditions, M. venosa produced a more organic-rich shell with higher density of and larger endopunctae, and smaller secondary layer fibres, when subjected to about one year of culturing. Also, increasingly negative δ13C and δ18O values are recorded by the shell produced during culturing and are related to the CO2–source in the culture setup. Both the microstructural changes and the stable isotope results are similar to observations on brachiopods from the fossil record and strongly support the value of brachiopods as robust archives of proxies for studying ocean acidification events in the geologic past.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: archive
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  • 7
    Publication Date: 2018-12-12
    Description: The feeding behavior of the cosmopolitan cold-water coral (CWC) Desmophyllum dianthus (Cnidaria: Scleractinia) is still poorly known. Its usual deep distribution restricts direct observations, and manipulative experiments are so far limited to prey that do not occur in CWC natural habitat. During a series of replicated incubations, we assessed the functional response of this coral feeding on a medium-sized copepod (Calanoides patagoniensis) and a large euphausiid (Euphausia vallentini). Corals showed a Type I functional response, where feeding rate increased linearly with prey abundance, as predicted for a tentaculate passive suspension feeder. No significant differences in feeding were found between prey items, and corals were able to attain a maximum feeding rate of 10.99 mg C h-1, which represents an ingestion of the 11.4% of the coral carbon biomass per hour. These findings suggest that D. dianthus is a generalist zooplankton predator capable of exploiting dense aggregations of zooplankton over a wide prey size-range.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 8
    Publication Date: 2016-08-05
    Description: In the Arctic, the currently observed rising air temperature results in more frequent calving of icebergs. The latter derive from tidewater glaciers. Arctic macrozoobenthic soft-sediment communities are considerably disturbed by direct hits and sediment reallocation caused by iceberg scouring. With the aim to describe the primary succession of macrozoobenthic communities following these events, scientific divers installed 28 terracotta containers in the soft-sediment off Brandal (Kongsfjorden, Svalbard, Norway) at 20 m water depth in 2002. The containers were filled with a bentonite–sand mixture resembling the natural sediment. Samples were taken annually between 2003 and 2007. A shift from pioneering species (e.g. Cumacea: Lamprops fuscatus) towards more specialised taxa, as well as from surface detritivores towards subsurface detritivores was observed. This is typical for an ecological succession following the facilitation and inhibition succession model. Similarity between experimental and non-manipulated communities from 2003 was significantly highest after 3 years of succession. In the following years, similarity decreased, probably due to elevated temperatures, which prevented the fjord system from freezing. Some organisms, numerically important in the non-manipulated community (e.g. the polychaete Dipolydora quadrilobata) did not colonise the substrate during the experiment. This suggests that the community had not fully matured within the first 3 years. Later, the settlement was probably impeded by consequences of rising temperatures. This demonstrates the long-lasting effects of severe disturbances on Arctic macrozoobenthic communities. Furthermore, environmental changes, such as rising temperatures coupled with enhanced food availability due to an increasing frequency of sea-ice-free days per year, may have a stronger effect on succession than exposure time.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 9
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    Springer
    In:  EPIC3Marine Animal Forests, Marine Animal Forests, Switzerland, Springer, 35 p., ISBN: 978-3-319-17001-5
    Publication Date: 2017-09-26
    Description: The Chilean fjord region, situated between 42 and 56 °S, forms one of the most ragged shorelines and belongs to the ecologically and biogeographically least understood marine regions of the world. A labyrinth of fjords, channels, and islands extends over 240,000 km2 and creates a coastline of more than 80,000 km. Due to strong abiotic gradients, numerous habitats are created, which are further diversified by temporal dynamics (tidal cycle, seasonal changes in precipitation, temperature, radiation, etc.). The region is a biodiversity hotspot hosting unique and fragile ecosystems. Among the species living here, several are species forming habitats in the ecosystem. These organisms can reach high densities conforming the so-called marine animal forests. Examples are marine animal forests dominated by cold-water stony corals, gorgonians, hydrocorals, brachiopods, polychaetes, giant barnacles, sponges, and ascidians. Many of these communities have been discov- ered only recently. There is also a singular characteristic in this area: exceptionally low pH levels of the waters of Patagonian fjords provide the opportunity to study calcifying organisms in an environment with pH conditions in the same range as the ones predicted by the IPCC for the world oceans in 2100. Despite the scarce ecological and biogeographical knowledge of this area, it encounters an unparalleled economic development including high-impact industry-scale salmonid farming, ambitious infrastructure and industrialization projects, and increasing extractive activities. Baseline research on the abiotic and biotic environment of the region is needed to reach sustainability in the use of the marine resources. Management plans including the establishment of marine protected areas to preserve benthic diversity and ecosystem services are urgently needed.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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  • 10
    Publication Date: 2018-05-03
    Description: Cold-water corals (CWC) are thought to be especially vulnerable to ocean acidification. However, in situ studies on the response of CWC to low aragonite saturation (Ωar) are still scarce. The Comau Fjord in southern Patagonia (Chile) is naturally stratified with vertical and horizontal pH gradients and high abundances of the cosmopolitan CWC Desmophyllum dianthus at Ωar ≤ 1. Previous studies reveal high growth rates of D. dianthus in summer but it is not known if skeletal growth and the ability of internal pH up-regulation show seasonal fluctuations due to changes in Ωar and/or food supply. In the present study, we compare D. dianthus skeletal carbonate accretion (buoyant weight technique) and linear extension rates (fluorescent microscopy) with the physico-chemical conditions in the water column (T, Ωar) in austral summer 2016/2017 and winter 2017. Corals were sampled at six stations at 20m water depth along the presumed horizontal pH gradient of Comau Fjord.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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