Schiel, Sigrid
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Schiel, Sigrid
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Schiel, Sigrid
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Schiel, S. B.
Schiel, Sigrid B.
Schnack-Schiel, Sigrid
Schnack-Schiel, Sigrid B.
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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.Dissertation272 141 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Ecology of larval fishes in the Independencia Bay, Pisco, Peru: Temporal and spatial relationships, taxonomic aspects(2005-02-15); ; ; The plankton of Independencia Bay was sampled during the year 2000. In total, 16,156 fish larvae, representing 34 families, 48 genera and 48 species were collected. 8 families numerically dominated the diverse larval fish fauna and comprised 96.8% of the larvae captured. The monthly mean density of total fish larvae showed two peaks (springtime and summer peaks). The greatest mean density during the spring peak was 7,492 larvae/100 m3, recorded in October. The greatest mean density during summer was recorded in February (2,493 larvae/100 m3). Abundance in October (spring time) at Santa Rosa was higher than at the other 3 stations, but abundance in those other 3 stations was higher in February (summer time). The spring and summer ichthyoplankton abundance peaks in Independencia Bay coincided with high zooplankton standing stocks and also coincided, approximately, with periods of increased upwelling in the area. The occurrence of high larval fish densities and the wide range of larval stages suggest that Independencia Bay is a regionally important spawning and nursery ground for marine fish. A Principal Component Analysis (PCA) showed that temperature and salinity accounted for the largest fraction (74.4%) of the variability in the observed larval fish assemblage patterns. Vertical distribution patterns of ichthyoplankton were examined from two depths (surface and 10 m) at two stations. There were no statistically significant differences between nighttime and daytime densities of fish larvae at either depth. Nevertheless, a small degree of vertical redistribution was apparent for some species that could be interpreted as nocturnal dispersal. Developmental series for individuals of Normanichthys crockeri and Prolatilus jugularis are presented using morphological features and pigmentation patterns. Larvae hatch sizes, information concerning the different stages, main diagnostic features of the larvae and meristic information including fin ray accounts are given.Dissertation292 133 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Exploration of structure and trophodynamics of coelobite (cavity-dwelling) communities in Red Sea coral reefs(2002-02-02); ; ; The results of this work contribute to the understanding of the ecology of coral reefs in general. The development of the CaveCam provides the key for a new line of coral reef research allowing to explore and document the labyrinth of framework cavities interlacing coral reefs in a non-destructive way. It yields 1:1 close-up images of specimens up to 4 m inside the reef. Image analysis revealed a rich variety of mainly encrusting organisms. Coralline algae predominated on the walls near the cavity entrances, while darker inner sections of the cavities were colonized by a diverse cryptofauna: filter feeders abounded, notably sponges, which covered up to more than 50% of the substrate. Light is a crucial factor determining the balance between photoautotroph and heterotroph organisms near the cavity entrance, while food supply and competition for space shape the composition of the heterotroph community further away.With the newly developed LightSheet-method the complex morphology of the highly irregular framework cavities was described and reconstructed in 3-D, volume and wall area calculated.The metabolic activity of the coelobite communities is reflected in small-scale gradients in chlorophyll a and oxygen concentrations between cavities and freestream waters over the reef, where stronger gradients appear to be associated with reduced flow and higher coelobite cover. Direct and indirect measurements of water replacement rates within the cavities allowed first quantitative estimates of the bulk filtering effect of the coelobite community. We provide circumstantial evidence, that coelobite filter feeders are indeed causing the observed phytoplankton depletions of chlorophyll a and oxygen. Remineralization of the largely extrinsic organic matter taken up by the coelobite filter feeders may fuel close to 20% of the gross metabolism of the entire reef. A checklist of coelobite organisms in the Red Sea is provided.Dissertation192 119 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Die saisonalen Veränderungen der Copepodengemeinschaft in einem oligotrophen Meeresgebiet - dem nördlichen Golf von Aqaba (Rotes Meer)(2005-04-05); ; ; The Gulf of Aqaba displays features of a typical subtropical ocean such as its oligotrophic condition during most of the year and a dominance of picoplanktonic primary producers and, contrary to other subtropical areas, a distinct hydrographical and biological seasonality. The aims of this thesis is to determine the influences of the seasonality observed in temperature and chlorophyll a on the copepod community and especially on the clausocalanid population of the northern Gulf of Aqaba.Mesozooplankton samples were taken with a Nansen net equipped with 200 µm mesh size. Copepods were by far the most abundant taxon of the total mesozooplankton (76%). Appendicularians ranked second in abundance (2.5%), closely followed by chaetognaths (2.4%). Within the copepods, the calanoids dominated, representing between 42 and 83%, followed by cyclopoids (8 - 46%) and poecilostomatoids (6 27%). The dominant calanoid copepods belonged to the families of Clausocalanidae (27%), Paracalanidae (20%), Acartiidae (5%) and Mecynoceridae (4%). Positive correlation coefficients were established for taxa preferring higher temperatures and negative ones for copepods which occurred in higher abundance during the colder part of the year. The dominant clausocalanids were represented by four species: Ctenocalanus vanus, Clausocalanus farrani, C. furcatus and C. minor (first record in Red Sea). The seasonal changes in abundance, the reproductive activity (in terms of gonad maturation) and the feeding behaviour of the clausocalanid females were investigated. Only for Ctenocalanus vanus a distinct negative correlation between the temperature, and the abundance and reproductive activity was established. Feeding experiments with the clausocalanid species revealed that the ingestion rates were food density dependent rather than size dependent. No distinct difference in the feeding pattern could be observed between Ctenocalanus and Clausocalanus were established.Dissertation246 170 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The Ecology and Evolution of Deep-Sea Copepods: Niche Separation in a Three-Dimensional Habitat(2009-06-30); ; ; Specialisation and niche separation are key processes for minimising or avoiding competition between co-occurring species. This study aimed at elucidating these processes for co-occurring meso- and bathypelagic representatives of two copepod families (Euchaetidae and Aetideidae) from the Arctic Fram Strait and the Southern Ocean by characterising their respective ecological niches based on ecological, bioà ¬chemical and molecular phylogenetic aspects. Phylogenetically closely related species are rather similar in ecological characteristics. They are generally characterised by similar trophic niches and minimise inter-specific competition by vertical partitioning. Species with similar vertical distribution ranges occupy different trophic niches. Arctic species strongly preyed on the abundant calanid copepods, as indicated by trophic markers (fatty acids and stable isotope ratios). Even deep-sea species benefit from these seasonally vertically migrating copepods as food items, which provide a short-cut in the food web and accelerate the vertical transport of organic matter into the deep sea.Dissertation415 132 - 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 135 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Influence of pelagic invertebrate predators on the zooplankton in the Baltic Sea and the North Sea(2006-06-13); ; ; Pelagic invertebrates have a wide prey spectrum and may constitute important predators in marine ecosystems. This study analyses the impact of pelagic invertebrate predators in the two connected ecosystems Baltic Sea and North Sea. Both ecosystems have different hydrographic conditions, but also show similarities in their reaction on changing ocean conditions (synchronous regime shifts) and were object of comparative studies in the framework of the German GLOBEC Project. In the central Baltic Sea the abundance, distribution, prey composition, predatory impact and origin of two Scyphomedusae (Aurelia aurita, Cyanea capillata) were investigated. In addition data on Mysidacea (Mysis mixta) and Chaetognatha (Sagitta elegans) were collected and analysed. In the southern North Sea abundance, distribution and prey composition of four Scyphomedusae (A. aurita, C. capillata, C. lamarckii, Chrysaora hysoscella) were investigated. Due to the low abundance of predators and high food concentrations, the predatory impact of all species was low. Higher impact on zooplankton populations was found only locally.Dissertation259 124 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Reproduction strategies and distribution of larvae and juveniles of benthic soft-bottom invertebrates in the Kara Sea (Russian Arctic). The influence of river discharge on the structure of benthic communities: a larval approach(2004-04-08); ; ; The aims of this work are to determine the reproductive patterns of benthic invertebrates in the Kara Sea and to analyse adaptations of reproduction strategies to polar conditions. Ecosystems of the Kara Sea are strongly affected by the freshwater input of the rivers Ob and Yenisei.Their outflows create a bilayered pelagic habitat with a confined pycnocline. 44 larval and 54 juvenile species were identified in plankton net and multicorer samples.For 23 of the larval species adults were present.For the remaining 21 adults were reported from the Barents and Petchora Sea, indicating larval input from the neighbouring seas.Most larvae were found in all water levels, although highest abundances were present in the upper layer,revealing a high acclimatisation potential of most larvae to low salinities.The pycnocline seemed to act as a physical barrier for most larvae.Meroplankton densities were generally less than 1 ind. m-3, but brittle star larvae reached densities of 200 ind. m-3.The importance of retention varied strongly between species.Most benthic species show an Arctic zoogeographic distribution, but considerable numbers of boreal species were also found.The river run-off may not only foster the survival of euryhaline species but through its thermal input create favourable conditions for boreal species.Most invertebrates seem to reproduce directly (without pelagic larvae), which can be explained partly by the high share of peracarid crustaceans.Their elimination from the dataset reveals a larger share of indirect reproducing species.It is assumed that due to the Kara Seas high environmental variability unfavourable conditions for benthic species often occur.Species with pelagic larvae or highly mobile peracarid crustaceans may have an advantage in reoccupying devastated habitatsThe numerous larval types found indicate that planktonic development is important in the Kara Sea ecosystemDissertation410 56 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Spatial and temporal distribution patterns of zooplankton in the central Baltic Sea and methods to detect them(2007-02-16); ; ; The Baltic Sea is the largest semi-enclosed brackish sea in the world and consists of several consecutive deep basins. Due to fresh water input, physical processes and topographic structures pronounced hydrographic stratifications persist. These are created from water masses of incompatible densities due to different temperatures and salinities.A total of 832 multinet samples from different sites and depths were analysed for composition of the dominant zooplankton species and the relation to ambient environmental parameters by means of multivariate methods, weighted depth centroids and individual analyses of the vertical distribution. Species and developmental stages were bound to distinct layers and partially migrate between them during the season. The layers put different demands on the physiology of the individual species and can be conceived as habitats, determining the vertical distribution.When assessing the vertical distribution of plankton using nets the depth integration is a limiting factor intrinsic to the method, making a precise assessment of zooplankton species in different horizons more difficult. To solve these problem new concepts for optical in-situ detection of plankton species is introduced.Dissertation279 331 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Lipids in key copepod species of the Baltic Sea and North Sea - implications for life cycles, trophodynamics and food quality(2006-08-14); ; ; This thesis was embedded within the German GLOBEC project, which focused on climate induced ecosystem changes in the Baltic and North Sea by evaluating the influence of trophic interactions and physical forcing. Life-cycles and trophodynamics of the predominant copepod species Pseudocalanus acuspes, Temora longicornis and Acartia longiremis in the Bornholm Basin as well as the role of food quality for the reproductive success of copepods and higher trophic levels were examined. According to their general life-cycle characteristics the copepod species were categorized into three overwintering types, with different emphasis of storage lipids for overwintering. According to fatty acid markers in the storage lipids distinct interspecific and interseasonal differences were identified, reflecting different feeding strategies and a seasonal variation in food composition. Changes in the condition of copepods were discussed in light of their relevance for higher trophic levels.Dissertation270 108