Niehoff, Barbara
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Niehoff, Barbara
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Niehoff, Barbara
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Item-typ:Veröffentlichung, Physiological adaptations of copepods from the North Sea and the North Atlantic to changing nutritional conditions(2008-02-07); ; ; Marine calanoid copepods, which constitute a major component of the marine food web, have to adapt to changing environmental conditions in order to efficiently use dietary components for growth and reproduction. Detailed knowledge on their feeding behaviour, their physiological responses to nutritional conditions, i.e. digestive and metabolic activities, and their functional responses, i.e. reproduction, is of major importance in order to better understand how diet affects growth and reproduction of copepods. The present thesis aims at elucidating physiological adaptations of calanoid copepod species to changing nutritional conditions and how these are related to different life cycle strategies, metabolic requirements and biochemical properties. For this purpose, species with different life strategies from the North Sea, i.e. Temora longicornis, Acartia clausi and Centropages typicus, and the St. Lawrence estuary, i.e. Calanus finmarchicus and Metridia longa, were investigated during several phytoplankton blooms. A comprehensive data set on digestive, metabolic and functional responses to changing nutritional conditions is presented and the data are discussed with respect to different life strategies.Dissertation481 173 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Life history traits of copepods in a changing Arctic : seasonal patterns in the physiology of Calanus glacialis(2015-05-13); ; ; The Arctic experiences rapid environmental changes and to date, we cannot predict to what extent calanoid copepods can adapt to shifts in environmental conditions. On the Arctic shelf, the large species Calanus glacialis accumulates energy reserves in surface waters during the productive season and overwinters in diapause in deep waters. This thesis aims to investigate the physiology of C. glacialis in a comprehensive approach during activity and diapause in relation to environmental factors. This study revealed clear seasonal patterns in the physiology of C. glacialis. Enzymatic activities and extracellular pH (pHe) were high during the productive season, while catabolic activities were high and pHe low in winter. The usage of internal energy reserves was high in the end of overwintering. The timing of diapause is adjusted to the prevailing environmental conditions, which suggests that C. glacialis may be able to adjust to future climate driven changes in the environment.Dissertation344 147 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Zooplankton performance in a changing ocean : adaptive capacities to a shifting food regime in the North Sea(2018-11-29); ; ; Zooplanktonic organisms are often vulnerable to fluctuations in food supply. Their population dynamics is directly influenced by changes in phytoplankton availability and nutritional quality, which in turn is affected by changes in parameters such as nutrient loading. The aim of this study was to investigate how nitrogen (N) limitation in prey (i.e., food quality) affects the performance of zooplankton. Females of the copepod Temora longicornis and larvae of the polychaete Lanice conchilega were sampled in May and June 2016 off the German island of Helgoland, in the southern North Sea, for five-day laboratory feeding experiments. They were fed with diets of different quality - diatoms and dinoflagellates cultured in nutrient-replete (Diat and Dino , respectively) and in N-depleted (Diata and Dinoa , respectively) conditions. Sodium bicarbonate enriched with the 13C isotope (NaH13CO3) was added to prey cultures in order to label dietary fatty acids (FA) and to follow carbon (C) transfer into copepods and polychaetes. Zooplankton performance was assessed by analysis of the elemental and biochemical compositions and of the assimilation and turnover of C in copepods and polychaetes, and by measuring copepod physiological rates. Copepods feeding on Dino had the highest investment in somatic and reproductive growth. Copepods feeding on Diata had the highest N excretion rates. Egestion was a major pathway for eliminating excess C, and low food quality affected respiration rates and the intensity and speed with which dissolved organic carbon leaked from faecal pellets. Copepod physiological rates indicated that dinoflagellates are a food source of superior or similar quality to diatoms under nutrient-replete or N-depleted conditions, respectively. In addition, copepods feeding on Diata showed the highest lipid C assimilation and turnover rates. These results suggest a shift in copepod resource allocation (reproductive output or lipid accumulation) depending on food quality. Experiments with the polychaete revealed that larvae are able to regulate their lipid C content (homeostasis) regardless of the availability of dietary FA via selective accumulation and biosynthesis of FA. Lipid C assimilation results from both species, together with literature data, were used to formulate a hypothesis on different patterns of lipid homeostasis in zooplankton. These results present a robust contribution towards a better understanding of how zooplanktonic organisms might be affected by changes in the quality of their prey in the near future.Dissertation408 188 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Turnover of trophic markers and lipid carbon in Arctic marine food webs : the contribution of key zooplankton species(2017-05-23); ; ; In the context of climate warming, severe shifts in the phyto- and zooplankton communities, and thus changes in trophic interactions, are expected. It is therefore essential to better understand the lipid and fatty acid turnover in the in the lipid-driven Arctic food web. This study aims at evaluating the role of zooplankton in the transfer of lipids from primary producers to higher trophic levels. It combines field observations and experimental work to fill the gaps of knowledge in the ecology and lipid biochemistry of Arctic zooplankton key species, i.e. the copepods Calanus glacialis, Pseudocalanus minutus and Oithona similis, the thecosome pteropods Limacina helicina and L. retroversa and the gymnosome pteropod Clione limacina.Dissertation315 147 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Oithona similis (Copepoda: Cyclopoida)- a cosmopolitan species?(2013-03-18); ; ; The present study investigated whether the cyclopoid copepod Oithona similis Claus 1866 is a cosmopolitan or a conglomerate of cryptic species. Adult and subadult females (C5 stages) of O. similis were closely examined morphologically and via DNA-barcoding from four study areas: the Arctic Ocean, the Southern Ocean, the North Sea and the Mediterranean Sea. Sampling was done during two expeditions with RV Polarstern in the Arctic Ocean (ARK XXIII-3, ARK XXV-1) and at one expedition in the Southern Ocean (ANT XXIV-2). Further samples from three stations in the North Sea and one station in the Mediterranean Sea were provided. Based on the shape of the rostrum, body size and the formula and structure of the outer setae of the exopodits of the swimming legs, five different morphotypes were identified: Oithona similis (Arctic Ocean, Mediterranean Sea, North Sea, Southern Ocean), O. atlantica (Arctic Ocean), O. frigida (Southern Ocean), O. nana (North Sea) and Oithona sp. (North Sea). Via CO1-sequencing in total eight different haplotypes of O. similis were found in this study: three in the Arctic Ocean, three in the Southern Ocean, one in the North Sea as well as in the Mediterranean Sea and one in the Mediterranean Sea. Only one haplotype was found in one than one sampling area. In addition to the number of haplotypes, this clearly indicates that O. similis is not a cosmopolitan but a conglomerate of cryptic species. Additionally to the Oithona similis groups, three other copepod species groups were identified morphologically as well as via sequencing: O. frigida in the Southern Ocean and in the North Sea O. nana (close to the island of Helgoland)and Oithona sp. (close to the island of Sylt). Oithona nana was chosen as the basis of a neighbor joining tree because it is not as closely related to O. similis as the other species are. Morphological differences regarding the appendages of the swimming legs of O. frigida and O. similis were obvious and were clearly reflected in the results of the CO1 sequences. The differences reflected in the appendage structures of the swimming legs were also obvious between O. similis and O. nana. Another haplotype named Oithona sp. shares the swimming leg appendage structure with O. nana, but has a bended rostrum like O. similis. The differentiation between these species is also clearly reflected in their position in the neighbour joining tree. Thus, O. similis and other Oithona species inhabiting the investigation areas can clearly be differentiated morphologically and genetically. The CO1- sequences of the Oithona similis haplotype containing individuals from two different places in the North Sea and the Mediterranean Sea differ from the sequences of the species sampled at the other regions. The fact that the same haplotype was found at different places in the North Sea as well as in the Mediterranean Sea shows that this species is widely distributed and might be quite flexible concerning environmental conditions. It is also possible that species of the genus Oithona are advected into the southern North Sea with Atlantic water Overall, almost no morphological differences were found within and between regions for individuals of the Oithona similis species groups from the Southern Ocean, the Arctic Ocean, the North Sea and the Mediterranean Sea. Exceptions are individuals from the Arctic Ocean that were described as Oithona atlantica. One aim of this study was to examine whether possibly existing cryptic species in the nominal O. similis either show no morphological differences or only very slight ones that make it impossible to differentiate between them morphologically. Since individuals that were described as Oithona atlantica prior to sequencing do not form an own haplotype, and as no other morphological differences within the O. similis individuals were found, this can be confirmed at least concerning the examined morphological characters.Dissertation385 174