Hagen, Wilhelm
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Hagen, Wilhelm
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Hagen, Wilhelm
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Hagen, W.
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Item-typ:Veröffentlichung, Life-Cycle Strategies and Impact of Cannibalism in Calanoid North Sea Copepods(2007-10-19); ; ; There were strong differences in life-cycles of dominant calanoid copepod species in the German Bight, although they show a similar seasonal course of abundance and reproduction. In a field study, stage-specific abundances, egg production rates, proportion of spawning females and hatching success of Acartia clausi, Temora longicornis, Centropages hamatus and C. typicus were estimated. The strategy of ceasing reproduction and hibernation of adult females (A. clausi) competed successfully with reproduction throughout the year combined with the production of resting eggs (T. longicornis), or with a strategy of virtual absence in winter and population built-up in spring by nauplii emerging from resting eggs (C. hamatus).In laboratory experiments, feeding rates of females on young copepod offspring were determined. The experiments showed the capability of adults to ingest eggs and nauplii. Predation was strongly influenced by prey density, behaviour of predator and prey, and concentration of alternative food. A theoretical approach demonstrated the potential of such predation to reduce the population sizes markedly during times of intense breeding.Dissertation273 141 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Ecophysiological performance and life cycle strategies of North Sea shrimps(2019-10-29); ; ; The high level of digestive enzyme polymorphism in C. crangon specimens seems to be an important feature for their biological success in the North Sea. This pronounced polymorphism has different impacts on the metabolism of North Sea shrimps. On the one hand, it affects the sequence of proteins necessary for the accumulation of lipids. This change in the sequence of specific proteins is a challenge to the metabolism of C. crangon, because it results in a limited lipid storage capacity. Lipid storage is important to overcome periods of food paucity and to fuel reproduction. However, in C. crangon the midgut gland does not function as principal energy depot. Instead, the midgut gland serves as a dynamic metabolic center that directly provides dietary energy necessary for diverse biological processes including reproduction. This metabolic center seems to be supported by the expression of digestive enzyme isoforms.Dissertation382 179 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Life-history traits of the copepods Pseudocalanus minutus (Calanoida) and Oithona similis (Cyclopoida) in the Arctic Kongsfjorden (Svalbard) with particular emphasis on seasonality(2006-11-24); ; ; The life-history traits of the copepods Pseudocalanus minutus (Calanoida) and Oithona similis (Cyclopoida) were investigated in the Arctic Kongsfjorden (Svalbard). In November, both species exhibited maximum abundances (P. minutus: 111,297 and O. similis: 704,633 ind m2), whereas minima occurred in June (1,088 and 4,483 ind m2, respectively). High levels of diatom marker fatty acids (16:1(n-7), 16:4(n-1), 20:5(n-3)) as well as high trypsin activities showed that the diatom bloom in spring was of specific importance for adult females and stage V copepodids of P. minutus to fuel final maturation processes and reproduction in May/June. O. similis generally followed an omnivorous feeding mode as indicated by consistently high amounts of the 18:1(n-9) fatty acid and the general predominance of the (dino-)flagellate biomarker 22:6(n-3). The first reproductive peak in June was primarily fueled by lipid reserves (wax esters), whereas the second reproductive peak in August/September co-occurred with energy storage for overwintering.Dissertation292 143 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The early life strategy of Cape hakes in the Benguela upwelling system off South Africa(2010-08-13); ; ; Recruitment is a key process in the sustainability of marine fish populations. Thedynamic and complex process of recruitment is integrated over several life stages, withmany different factors affecting each stage leading to high variability in populations. Thisstudy aimed at gaining important knowledge on the early life history and the factorsaffecting recruitment of the two demersal Cape hake species Merluccius paradoxus andM. capensis in the southern Benguela upwelling system off South Africa. Eggs andlarvae were collected by stratified hauls during four cruises in two consecutive years.Early juveniles were collected on one cruise in the northern part of the study area off theOrange River.The spatial distribution patterns, growth and condition of early stages were investigatedusing a combination of classic and novel methods. Spatial distribution patterns weredescribed by species-specific vertical and horizontal abundances. Growth wasinvestigated by otolith analyses of larvae and juveniles. Larval conditions were analysedby measuring RNA:DNA ratios. Another method for estimating condition was applied toeggs and larvae by measuring the total lipid content. Fatty acid compositions wereinvestigated in order to reveal the levels of essential fatty acids, needed for growth anddevelopment. Stomach content analyses complemented the information on early lifestages as they elucidated the feeding of larvae in the study area.Distribution patterns revealed that M. paradoxus was the dominant species during thestudy periods, indicating a temporal and possibly spatial separation of spawning of thetwo Cape hake species. This difference in the spawning strategy reduces competitionduring the early life stages between the two similar species, allowing their co-existencewithin the same ecosystem.Furthermore, the distribution patterns of hake eggs and larvae indicated that asubstantial part of spawning occurs on the western Agulhas Bank. Early stages aretransported by the jet current, whereby the drift routes of the two species are separated,with M. paradoxus found further offshore than M. capensis. Complex retentionmechanisms enable larvae on the inshore drift route to reach the coastal nursery areaoff Cape Columbine, whereas larvae from the offshore route are transported furthernorth. This transport and dispersal mechanisms are important for larval connectivity.Therefore, the spawning strategies of the two hake species are adapted to the variable environment of the southern Benguela system, as spawning takes place during a time ofoptimal transport conditions for eggs and larvae towards their specific nursery areas.In addition, factors affecting the recruitment of hake were investigated by analysinggrowth and condition of early stages. Analyses indicated that the South African hakesare fast growing species. Survivors outgrow their conspecifics and cannibalism seemsto play an important role in the survival strategy of hake. Larvae were generally in goodcondition, as indicated by high RNA:DNA ratios, and they can be regarded as thesurvivors, as starving larvae with poor condition are more vulnerable to predation.RNA:DNA ratios as condition proxy and growth did not correlate in hake larvae, as theRNA:DNA ratios were well above the threshold level for growth. Furthermore, low lipidcontents were found in yolk-sac larvae of one investigated year, indicating maternaleffects by poor conditions of spawners, possibly affecting recruitment. The life historystrategy of hakes can be described as periodic with adaptations from an opportunisticstrategy.In conclusion, the interdisciplinary approach of this study provided new and importantknowledge on the early life history and the recruitment of the Southern African hakespecies, which can be transferred to other demersal, long-lived and fast-growing fishspecies. Furthermore, this information can be applied to fisheries management and itcan help to predict the consequences of climate change for M. paradoxus and M.capensis in the southern Benguela upwelling system.Dissertation270 144 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Distribution patterns and migratory behavior of Antarctic blue whales(2016-12-15); ; ; After having been one of the primary targets of commercial whaling during the 20th century, Antarctic blue whales (Balaenoptera musculus intermedia) are still listed as critically endangered by the International Union for Conservation of Nature and many aspects of their distribution and migration patterns remain poorly understood to date. This dissertation investigates spatio-temporal patterns in the (acoustic) presence of Antarctic blue whales in the Atlantic sector of the Southern Ocean and in the South Atlantic Ocean in order to contribute to a better understanding of their distribution patterns and migratory behavior. It adds to increasing evidence that Antarctic blue whales inhabit both high- and low-latitude areas in the Southern Hemisphere year-round and thereby indicates that a diverse migratory repertoire is rather the rule than the exception in Antarctic blue whales. An improved understanding of the distribution and migration of Antarctic blue whales can aid the development of effective conservation strategies for this critically endangered species, such as the designation of marine protected areas in Antarctic blue whale key habitats.Dissertation396 171 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Population Dynamics and Social Organisation of Humpback Whales (Megaptera novaeangliae) - a Long-term Study in the Gulf of St. Lawrence, Canada(2008-10-10); ; ; The stock of humpback whales in the Gulf of St. Lawrence (GSL) was severely depleted by whaling in the 18th and 19th century and started to recover later in the 20th century than other stocks in the North Atlantic. A long-term study of humpback whales by the Mingan Island Cetacean Study in the GSL, using photo-identification and biopsy techniques, started in 1980 and is still ongoing. The data set from 1980 to 2005 was evaluated in this thesis to estimate population parameters, such as sex ratio, calving rates, survival rate and population trend for this stock for the first time. The estimates were compared with other populations and stocks, and used to assess the current conservation status of humpback whales in the GSL.Dissertation403 151 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Optimized encapsulation substances and feeding regimes for administering an oral vaccine in rainbow trout, Oncorhynchus mykiss (Walbaum)Impfungen bei Tieren sowie bei Menschen sind eine der wertvollsten Errungenschaften der Menschheit, um krankheitsbedingte Herausforderungen einer sich intensiv verändernden Umwelt zu bewältigen. Während Impfstrategien mit Injektions-Impfstoffen für terrestrische domestizierte Tierarten gegenwärtig effektiv entwickelt sind, ist die Impfung von Tierarten in der Aquakultur weltweit bisher keine gängige Praxis. Aufgrund des hohen Arbeitsaufwandes sowie technologischem und finanziellem Aufwand finden injektive Impfungen in der Aquakultur in Entwicklungs- und Schwellenländern kaum Anwendung. Die Anwendung von Oralvakzinen bietet demnach als Alternative zu injektiven Impfungen viele Chancen. Sie können anwendungsbezogenen Probleme bewältigen und dem Tierwohl, der Umwelt, wie auch der Produktionseffizienz zu Gute kommen. Um eine effektive Oralvakzine entwickeln zu können, sind jedoch noch Hürden zu bewältigen, wie die Frage nach der gezielten, oralen Verabreichung und des wirksamen Schutzes vor der Zerstörung der aktiven Vakzine durch das Systemwasser oder durch enzymatische sowie chemische Degeneration. Die drei Kapitel dieser Dissertation beschäftigen sich mit der Optimierung des Fütterungsregimes, sowie mit der Evaluierung unterschiedlicher Impfstoffträger- / Verkapselungssubstanzen am Beispiel der Zieltierart Regenbogenforelle (Oncorhynchus mykiss). Die Ergebnisse dieser Arbeit ermöglichen nicht nur eine kontrollierte und sichere Verabreichung einer Oralvakzine, sondern sind für das Hervorbringen einer effektiven Herdenimmunität nach oraler Impfung unabdingbar. In Kapitel 1 wurden die Auswirkungen verschiedener Fütterungsregimes auf das individuelle Fressverhalten von juvenilen, in einer Kreislaufanlage (RAS) kultivierten Regenbogenforellen untersucht. Die veränderten Parameter des Fütterungsregimes umfassten Ausnüchterungsperioden, die Anzahl der täglichen Fütterungen und die Anzahl der Futterzugaben pro Fütterung. Diese zeigten einen signifikanten Einfluss auf die Homogenität und Gesamtmenge der Futteraufnahme. Um das Fressverhalten während der verschiedenen Fütterungsszenarien zu bewerten, wurde die minimale Pelletaufnahme (MPI) als Maß für eine garantierte Pelletaufnahme pro Individuum etabliert. Dabei beschreibt die MPI den Anteil an gefütterten Fischen, der eine Mindestanzahl an Pellets gefressen hat. Im Hinblick auf die Anwendung als Schluckimpfung kann die MPI für die Impfstoffquantifizierung eines Impfpellets verwendet werden. Die Ergebnisse des Ausnüchterungsversuches zeigten, dass die Fresshomogenität bei unveränderter aufgenommener Futtermenge erhöht werden kann, wenn die Tiere keinerlei Ausnüchterungsperiode erfahren. Die Anzahl der täglichen Fütterungen kann genutzt werden, um die Gesamtmenge des aufgenommenen Testfutters bei gleichbleibender Futterhomogenität zu erhöhen. Je nachdem, wie viel Impfstoff bzw. wie viele Pellets pro Fisch intendiert sind, kann die Anzahl der täglichen Fütterungen (ein- oder zweimalige Fütterung pro Tag) die MPI erhöhen, ohne dass dies zulasten der Aufnahmehomogenität geht. Eine zusätzliche dritte Fütterung führte indes zu einer deutlichen Verringerung der Aufnahmehomogenität und wird demzufolge bei der Anwendung einer Schluckimpfung nicht empfohlen. Vorteilhaft für die MPI und die Aufnahmehomogenität ist die Verwendung mehrerer Portionen während eines Fütterungsereignisses. Hier zeigte die Aufteilung auf drei und fünf Portionen pro Fütterung einen deutlichen Vorteil gegenüber nur einer Futterzugabe bei gleicher Gesamtmenge. Insgesamt kann die Optimierung des artspezifischen Fütterungsregimes dazu genutzt werden, die Pelletaufnahme und -homogenität zu erhöhen und eine minimale Pelletaufnahme pro Fisch zu garantieren. In Kapitel 2 wird die Forschungsfrage untersucht, inwiefern die Substanzen Alginat und Polyethylenglykol (PEG) geeignet sind, um die aktiven Impfstoffkomponenten während der Fütterung vor der Loslösung in das Systemwasser und später vor dem enzymatischen und chemischen Abbau im Fischdarmtrakt zu schützen. Um eine potenziell schädliche Wirkung von Alginat und PEG auf den Verdauungstrakt von Jungforellen auszuschließen, wurden die Testsubstanzen, eingebettet in ein kommerzielles Futter, 22 Tage lang kontinuierlich gefüttert und verschiedene Darmabschnitte der Versuchstiere histomorphologisch ausgewertet. Zudem wurden die Genexpression der proinflammatorischen Gene TNF-α, IL-1β und IL-8 untersucht, um eine eventuell auftretende systemische Entzündung auszuschließen. Die Fütterung beider Substanzen über den festgelegten Testzeitraum führte zu keiner signifikanten intestinalen Beeinträchtigung oder entzündlichen Genreaktion. Die Beimengung von PEG zum Fischfutter führte mitunter zu signifikanten Veränderungen des Darmgewebes, zu vermindertem Wachstum und zu einem leicht erhöhten Milzgewicht. Beide Substanzen wurden für die Verwendung bei Oralvakzinationen bei einmaliger bzw. bei einer Booster-Immunisierung als unbedenklich eingestuft. In Kapitel 3 wurden die drei Verkapselungssubstanzen Alginat, PEG, Chitosan sowie ein zusätzliches hydrophobes Öl-Coating auf ihre biophysikalischen Fähigkeiten untersucht, wie sie jeweils ein verkapseltes Modellprotein unter unterschiedlichen pH-Milieus freigeben. Darüber hinaus wurden in situ die Verdauungsgeschwindigkeiten der Testsubstanzen in Verbindung mit einem mit Eisenpuder verabreichten Futtermittel anhand von Röntgenaufnahmen evaluiert. Die Verkapselungsversuche zeigten, dass insbesondere die Verwendung von Alginat mit Chitosan eine ideale Verkapselung und ein optimales Freigabeprofil bei einer modellierten Fütterung darstellten. In der Regel führt das Einbringen der Kapsel in das Systemwasser zu einer starken initialen Freigabe des Modellproteins in das Systemwasser. Dieser „initiale Burst“ kann jedoch durch die Verwendung eines hydrophoben Öl-Coatings stark reduziert werden. Die Beigabe von PEG ermöglicht es, höhere Freigaberaten zu erzielen, jedoch leidet gleichzeitig der Verkapselungsschutz. Die Verwendung einer Alginat-Chitosan-Verkapselung bietet bei einer Schluckimpfung einen signifikanten Schutz gegen Zerstörung durch das Systemwasser und vorzeitige Degeneration im Fischverdauungstrakt. Bei der Evaluierung der Verdauungsgeschwindigkeiten konnten keine signifikanten Unterschiede zwischen den Behandlungen festgestellt werden. Es zeigte sich, dass alle Testfuttermittel den Enddarm nach 16 h erreicht haben und weitere Anpassungen der Verkapselung sollten auf eine maximale Impfstofffreigabe 16 h nach Verabreichung abzielen. Die Ergebnisse erlauben eine gezielte Optimierung der Verkapselungsmatrix beim Schutz der bioaktiven Substanz und der Freigabe am Zielort (Fisch-Enddarm). Die neuen Erkenntnisse dieser Dissertation tragen zur Lösung aktueller Probleme bei der Entwicklung eines oralen Impfstoffs für die Aquakultur durch die Optimierung der Fütterungsregime und Vakzine-Trägersubstanzen bei. Sie bilden hierbei nicht nur die Grundlage für die optimale Verabreichung und Verkapselung eines oralen Impfstoffes, der für einen effektiven Impfschutz unerlässlich ist, sondern auch für die Verabreichung anderer hochwertiger bioaktiver Substanzen, für die eine definierte Verabreichung von zentraler Bedeutung ist.Dissertation301 151 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Ecology and ecophysiology of invasive and native decapod crabs in the southern North Sea(2017-12-01); ; ; The Asian shore crab Hemigrapsus sanguineus is native to the coasts of China, Korea and Japan. It first invaded the U.S. east coast in the late 1980s and its present range extends from North Carolina to Maine. It was detected in France and the Netherlands in 1999. Nowadays, H. sanguineus is fully established at the European Atlantic coast. It can be found from the Contentin Peninsula, France to the German Wadden Sea, including the rocky island of Helgoland. In the U.S. and in Europe, H. sanguineus shares habitats with the native European green crab Carcinus maenas and competitive interactions between both are suggested. Thus, the main aims of this thesis were 1) to evaluate the status of H. sanguineus and C. maenas around Helgoland in relation to wave action, 2) to compare the respiratory metabolism and energy demand of both species, and 3) to assess their energy storage capacities and dietary preferences.Dissertation450 264 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Pelagic Biodiversity and Ecophysiology of Copepods in the Eastern Atlantic Ocean : Latitudinal and Bathymetric Aspects(2016-03-18); ; ; Pelagic copepods play a key role in marine food webs as they transfer energy from lower to higher trophic levels and are responsible for the cycling and flux of a substantial amount of organic matter. Copepod communities are usually characterized by strong latitudinal and bathymetric gradients. Their biodiversity is mainly regulated by environmental parameters, biological interactions and species-specific ecophysiological performances. However, major driving mechanisms generating high biodiversity are still poorly understood, especially in the pelagic deep sea. The present thesis provides detailed information on distributional patterns, community structure and diversity of copepods in four major oceanic provinces of the tropical and subtropical eastern Atlantic and additionally a coastal region of the northern Benguela Current upwelling system. The analysis of community structure was combined with ecophysiological characteristics, i.e. trophodynamics and metabolic demands of key species, to investigate trophic and spatial niche separations, food requirements and the role of copepods in mediating vertical carbon flux from the euphotic zone down to 2000 m. Below the euphotic zone, representatives of the family Spinocalanidae were particularly abundant and species identification of adult and juvenile stages based on morphological features was a real challenge. To elucidate diversity as well as species- and stage-specific vertical distribution patterns of this relatively unknown, deep-sea copepod family, an integrated taxonomic approach was applied, combining morphology, DNA sequence analyses and proteomics using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). As time- and cost-efficient method, proteomic fingerprinting discriminated even putative cryptic species and yielded quantitative information on vertical distributional patterns of Spinocalanidae with high species and stage resolution. Thus, detailed community analyses based on proteomic fingerprinting may shed new light on biodiversity, plankton dynamics, phylogeographic patterns and vertical habitat partitioning, which is particularly promising for taxonomically challenging copepod groups such as cryptic species, juvenile stages and fragile deep-sea species.Dissertation329 437 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Local adaptation in the presence of gene flow in Patagonian and Antarctic Nacella limpets: a multimarker genetic and physiological approach(2011-09-26); ; ; The understanding of how speciation works in the ocean has always challenged marine biologists because the marine realm is characterized by the absence of strict barriers to gene flow over large geographical scales. The impact of natural selection as a source of speciation in the marine system has also been considered to be low because of the very high gene flow overriding the effects of locally varying selective pressures. In a top-down approach I analyzed large-scale impacts of emerging geographical barriers and small-scale influences of biogeographic patterning and local adaptations on the evolutionary history of Antarctic and South American Nacella limpets. A large set of genetic and physiological, neutral and selected markers was applied. The results show that natural selection and local adaptation are much more important drivers of marine speciation than previously believed. The application of genetic markers under selection revealed how natural selection is capable to maintain adaptive divergence in parts of a genome to ensure adaptability to environmental constraints even in high gene flow environments.Dissertation310 162