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Chlorophyll a and carbon dioxide measured in surface waters of the investigation area of cruise ANT-XIII/2
No full textChlorophyll a and carbon dioxide measured in surface waters of the investigation area of cruise ANT-XIII/
Temperature, salinity and Chlorophyll a in surface water along the POLARSTERN cruise track of ANT-XVI/3
No full textTemperature, salinity and Chlorophyll a in surface water along the POLARSTERN cruise track of ANT-XVI/
Irradiance measured along the track of cruise ANT-XIII/2
No full textIrradiance measured along the track of cruise ANT-XIII/
Epibenthos dynamics and environmental fluctuations in two contrasting polar carbonate factories (Mosselbukta and Bjørnøy-Banken, Svalbard)
Full text linkThe Arctic Svalbard Archipelago hosts the world’s northernmost cold-water ‘carbonate factories’ thriving here despite of presumably unfavourable environmental conditions and extreme seasonality. Two contrasting sites of intense biogenic carbonate production, the rhodolith beds in Mosselbukta in the north of the archipelago and the barnacle-mollusc dominated carbonate sediments accumulating in the strong hydrodynamic regime of the Bjørnøy-Banken south of Spitsbergen, were the targets of the RV Maria S. Merian cruise 55 in June 2016. By integrating data from physical oceanography, marine biology, and marine geology, the present contribution characterises the environmental setting and biosedimentary dynamics of these two polar carbonate factories. Repetitive CTD profiling in concert with autonomous temperature/salinity loggers on a long-term settlement platform identified spatiotemporal patterns in the involved Atlantic and Polar water masses, whereas short-term deployments of a lander revealed fluctuations of environmental variables in the rhodolith beds in Mosselbukta and at same depth (46 m) at Bjørnøy-Banken. At both sites, dissolved inorganic nutrients in the water column were found depleted (except for elevated ammonium concentrations) and show an overall increase in concentration and N:P ratios toward deeper waters. This indicates that a recycling system was fuelling primary production after the phytoplankton spring bloom at the time of sampling in June 2016. Accordingly, oxygen levels were found elevated and carbon dioxide concentrations (pCO2) markedly reduced, on average only half the expected equilibrium values. Backed up by seawater stable carbon and oxygen isotope signatures, this is interpreted as an effect of limited air-sea gas exchange during seasonal ice cover in combination with a boost in community photosynthesis during the spring phytoplankton bloom. The observed trends are enhanced by the onset of rhodophyte photosynthesis in the rhodolith beds during the polar day upon retreat of sea-ice. Potential adverse effects of ocean acidification on the local calcifier community are thus predicted to be seasonally buffered by the marked drop in pCO2 during the phase of sea-ice cover and spring phyto-plankton bloom, but this effect will diminish should the seasonal sea-ice formation continue to decline. Among the 25 macrobenthos taxa identified from images captured by the lander’s camera system, all but three species were calcifiers contributing to the carbonate production. Biodiversity was found to be much higher in Mosselbukta (21 taxa) compared to Bjørnøy-Banken (8 taxa), which is considered as a result of enhanced habitat diversity provided in the rhodolith beds by the bioengineering crustose alga Lithothamnion glaciale. Filter-feeding activity of selected key species did reveal group-specific but no common activity patterns. Biotic disturbance of the filtering activity was common, in contrast to abiotic factors, with hermit crabs representing the primary trigger. Motion tracking of rhodoliths revealed a high frequency of dislocation, triggered not by abiotic factors but by the activity of benthic invertebrates, in particular echinoids ploughing below or moving over the rhodoliths. The echinoid Strongylocentrotus sp. is the most abundant component of the associated fauna, thereby considerably contributing both to carbonate production and to grazing bioerosion. Together, these results portray a high degree of seasonal as well as short-term dynamics in environmental conditions that despite many similarities support distinctly different communities and biodiversity patterns in the calcifying macrobenthos at the two studied polar carbonate factories
Biologie meso- und bathypelagischer Chaetognathen im Südlichen Ozean
No full textChaetognaths contribute significantly to the zooplankton abundance and biomass in the world ocean. Stratified sampling between 500 and 2000 m depth with small mesh sizes in the Atlantic Southern Ocean has provided a unique opportunity for a detailed investigation of meso- and bathypelagic chaetognaths. The chaetognath community consisted of ten species with Eukrohnia hamata and Sagitta marri dominating. E. bathypelagica and E. bathyantarctica were characteristic deep-living species. Water depth and season were the determinants of chaetognath abundance and species composition patterns, indicating vertical seasonal migration and vertical segregation of species. Reproduction may be continuous in E. bathypelagica and E. bathyantarctica. These two deep-living species do not store high amounts of lipids and therefore rely on food supply year-round. However, their diet seems to be different because of their varying fatty acid compositions. The impact of meso- and bathypelagic chaetognaths on the copepod community in the Southern Ocean is probably significant and they may hold a central position channelling energy from lower to higher trophic levels
Fraßverhalten von calanoiden Copepoden und Analyse ihrer Kotballen
No full textObservations on the feeding behaviour of calanoid copepods, microscopical analysis of their faecal pellets and the possible ecological importance of copepod grazing will be addressed in this thesis. Laboratory as well as field studies were applied to investigate the responses of different copepod species to different food environments, covering the three main phytoplankton groups - Diatoms, Dinoflagellates and Coccolithophores. Since many of the species belonging to these groups are surrounded by mineral skeletons, qualitative observations can be revealed by the use of scanning electron microscopy (SEM).The importance of calcifying algae in the marine carbon and calcium cycles is widely known, but the role of copepods for the coccolith calcite dissolution is vague. Dissolution experiments were performed using the calcifying algae Calcidiscus leptoporus. SEM observations of the morphological changes of the coccoliths were used for content interpretation of freshly produced faecal pellets in feeding experiments with the common North Sea copepods Calanus helgolandicus and Temora longicornis. Coccolith calcite dissolution during copepod gut passage was found to be minor and can therefore not contribute significantly to the generally observed calcite dissolution in the upper ocean.Field experiments conducted during a dinoflagellate bloom in the North Sea clearly showed that some copepod species can feed very efficiently on the dinoflagellate species Dinophysis norvegica. SEM observations showed that faecal pellets produced by C. helgolandicus were almost exclusively filled with intact cells of this toxic dinoflagellate species. Faecal pellets, containing intact toxic phytoplankton species may be an important vehicle and new pathway transferring toxins within the pelagic and to the benthic community. The viability of D. norvegica cells within the faecal pellets was not investigated, but lead to the idea to observe the ability of different phytoplankton species to survive the copepod gut passage. Therefore a new staining method was applied. Viable cells of the dinoflagellate Scrippsiella trochoida and the diatom Fragilariopsis kerguelensis were detected within the faecal pellets of different copepod species. F. kerguelensis may protect itself with its stable frustules and also the formation of chains seemed to be advantageous for the survival of single cells when they are grazed. Whereas the long spines of the diatom Chaetoceos dichaeta provided no protection and was reduced to small pieces within the faecal pellets of all copepods investigated. Studies of species specific interactions among copepods and their prey can greatly improve the current understanding of the benefit of certain phytoplankton cell structures. In an additional experiment conducted with the two copepods Acartia clausi and T. longicornis the ability to graze on the largest centric diatom commonly found in the North Sea plankton was under investigation. A. clausi was not able to graze on Coscinodiscus wailesii but T. longicornis showed a very skilful handling of individual cells. The copepod did not ingest the whole cells, but bite a piece off the frustules to reach the protoplasma. After ingestion of the cell content, the empty diatom frustules were rejected. Results showed that traditional methods to determine grazing may sometimes be unsuitable and that new methods need to be developed. The new promising approach of genetical gut content analysis to qualify and quantify the grazing impact of copepods was therefore tested in a study and provided preliminary, but promising results.The general importance of food for copepods can be reflected in their energy requirements for egg production. To observe if and how food concentration is linked to egg production in a common Antarctic copepod species, the reproductive response of Rhincalanus gigas was studied during the build up of a diatom dominated phytoplankton bloom in the Southern Ocean. Results from egg production experiments as well as the maturation of their gonads revealed that R. gigas was able to react directly to enhanced food concentrations
Untersuchung zur Diversität und Funktion benthischer Mikroalgen und Protozoen im Nahrungsnetz mariner und limnischer Sedimente
No full textThis thesis aimed at achieving a deeper understanding of the dynamics and structure of microbenthic communities with a focus on protists. The most important discovery concerning protozoa in recent years is the fact that they play a much more important role in for example carbon and energy flow in nature than previously believed. In this thesis several studies were presented which focus on the seasonal dynamics and the spatial distribution of components of the small benthic community in marine and freshwater environments in temperate and arctic climates and which aim at establishing a generalised model of relationships and controlling factors in small benthic food webs. Samples of the upper 3 mm of the surface of soft sediment were collected in coastal freshwater and marine sites in Germany, USA and North East Greenland. The abundance and biomass of bacteria, cyanobacteria, diatoms and nanoflagellates (phototrophic and heterotrophic) were enumerated by means of epifluorescence microscopy. Ciliate species and meiofauna were enumerated with the help of light microscopy after QPS (quantitative protagol staining). Environmental data, such as temperature, salinity, sediment water content, grain size distribution, total and organic carbon- and nitrogen content as well as chlorophyll-a values were determined in order to study their influence on the community structures and total biomass. The investigation of a habitat in a mudflat in Dorum (Germany) revealed that the benthic microbial food web varied with the season with a primacy of bottom-up control during winter and spring, an increasing influence of top-down forces mainly by meiofauna grazing towards summer, decreasing again towards autumn, accompanied by a recovery of microphytobenthos.Investigations of soft sediment communities in different climate and geographic positions of freshwater and marine sites in Germany, North America (USA; Pennsylvania, New Jersey) and in North East Greenland were carried out. The results revealed considerable differences in the biomass of the small benthic components as well as in ciliate species composition and richness. The study of the ciliate species composition also exhibited a high variability of feeding types between the investigated sites, but the herbivorous feeding type seemed to be dominant in all sediments. Differences in total microbenthic biomass, abundance and ciliate species richness could not be attributed to the differences measured in carbon content, salinity or climatic parameters. The amount of chlorophyll-a was the only factor influencing the small benthic biomass. The sources of chlorophyll-a remained unclear. The hypothesis of Manini et al. (2003) stating that the composition of available carbon has a strong influence on the structure and biomass of microbial communities in shallow sediments seemed to hold true for the investigated sites. In a series of laboratory experiments the influence of the absence of all macrograzers as well as the presence of a single common abundant small macrograzer such as Hydrobia ulvae, Corophium sp. as well as Chironomid larvae and polychaets on the components of the microbenthic communities in sediments from all study sites were investigated. The structuring influence of Arenicola marina on components of the small food web was investigated in a long term field experiment on the island of Sylt. The results of the laboratory experiments and those of the field study revealed that the small macrofauna tended to have positive stimulating effects on the microbial community by bioengineering, rather than negative ones by grazing. The exclusion of Arenicola marina in a long term experiment revealed the fact that the role of this grazer was adopted by other grazers.The results of this thesis and literature data led to the conclusion that in small communities of soft sediments the trophic levels are blurred and most species rather feed opportunistically on what is most available. The dominance of the omnivourous feeding type, detritus feeding, stimulating bioengineering effects and feed back mechanisms compose a highly networked food web. The fundamental attributes of microbes such as large absolute population sizes, short generation times and high dispersal capabilities, form a system with rapid changes in species composition.The outcome of this thesis verified the model of Fretwell (1977) for benthic microbial food webs in coastal regions, predicting that top-down forces form the trophic structure, but the bottom-up attributes of the ecosystems, such as nutrients availability, temperature and light, determine the fundament of the community as total biomass, abundance and production
Die Rolle des Mesozooplanktonfraßes im biogeochemischen Kreislauf von Silizium des Südpolarmeeres
No full textThe role of copepod grazing, particularly of :i:Calanus simillimus:/i: and :i:Rhincalanus gigas:/i:, in the biogeochemical cycles of silicon (Si) and carbon (C) in the Antarctic Circumpolar Current (ACC) of the Southern Ocean is investigated. The two grazers show differences in feeding behavior before and in response to a diatom bloom stimulated by :i:in situ:/i: iron fertilization. The continuously high feeding activity of :i:C. simillimus:/i: on diatoms is conducive to enhance the export of primary produced C and Si. The grazing impact of this key species is high enough to influence population dynamics in the microplankton communities of the ACC. In the pre-bloom situation, :i:R. gigas:/i: fulfils most of its carbon requirement through grazing on detritus and thereby effectively reduces the vertical fecal flux produced by :i:C. simillimus:/i:. It is proposed that a Copepod-Retention-System for organic material is put in place by the copepod community under High Nutrient Low Chlorophyll (HNLC) conditions. Prey switching by :i:R. gigas:/i: from detritus to diatoms in the bloom situation lifts the grazing check on the detritus flux and enables loss of particulate C and Si from the surface layer with fast sinking fecal pellets. Results from dissolution experiments indicate that the enclosure of biogenic silica (BSi) in copepod fecal pellets prevents the dissolution of diatom frustules. Diatoms submitted to grazing of copepods and krill (:i:Euphausia superba:/i:) dissolved 4 to 26 times slower than un-grazed controls. :br:Estimates of C ingestion from :i:in vitro:/i: incubations and from gut fluorescence measurements are compared to respiratory carbon needs of copepods. Methods yield generally similar estimates for :i:C. simillimus:/i: whereas methods differ strongly for :i:R. gigas:/i: in the pre-bloom situation, reflecting the above mentioned differences in feeding behavior
Trophodynamik von Salpen im atlantischen Sektor des Südozeans
No full textThe impact of food regimes on the feeding dynamics, bioelemental composition and community structure of the two Southern Ocean salps Salpa thompsoni and Ihlea racovitzai are studied. During a mesoscale iron fertilisation experiment (EIFEX) in the Southern Ocean Polar Frontal zone, S. thompsoni showed an enhanced ingestion inside the fast developing bloom but a low degradation efficiency of the diatom rich food. Seasonal feeding dynamics of S. thompsoni and I. racovitzai were investigated during three surveys in the Lazarev Sea in summer, fall, and winter (LAKRIS and IPY 2007/2008). Pigment concentrations in the salp guts of both species showed significant positive correlation to ambient surface chlorophyll concentrations with high feeding activity of Ihlea racovitzai in winter. Ecological impacts of the salps grazing pressure and contribution to the vertical flux by the production of fecal pellets are discussed for both studies. Population structure and demographic development strongly suggest that blooms of both salp species are pulsed events of ephemeral duration in Antarctic waters
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