Dissertations / Theses on the topic 'Diatom diversity'

The focus of this PhD project is the functional and molecular diversity of Leptocylindraceae diatom species, the study of which can lead to a better understanding of long standing questions regarding the ecology and evolution of phytoplankton. A wide range of tools, spanning from microscopical observations and physiological measurements to molecular techniques and high throughput sequencing, is utilized during this attempt. The genus <i>Leptocylindrus</i> has been chosen as the main target species due its worldwide and at the same time local importance in the Gulf of Naples and also because of the already extended study of the species in Stazione Zoologica Anton Dohrn (SZN) towards the direction mentioned above. Leptocylindraceae are centric diatoms that occupy a basal position in the diatom phylogeny and are abundant in marine plankton worldwide. In the Gulf of Naples (GoN), five out of the six species are found; <i>L. minimus</i> is known to be absent from the Mediterranean environment. The family shows a morphological conservation but the seasonal patterns between the species differ considerably. Indeed, physiological experiments of two <i>Leptocylindrus</i> species that show contrasting seasonality confirmed their opposed preferences regarding temperature as well as a high intraspecific phenological variability. In addition, the analysis of transcriptomes acquired for the three temperatures of one of them (<i>L. aporus</i>) indicated the possibly important role of transposable elements in response to stress and diatom adaptation. Furthermore, the transcriptomes of all <i>Leptocylindrus</i> species were explored in order to detect basic intra- and interspecific similarities and/or differences. HTS sequencing data from the MareChiara station in GoN and from the Tara expedition in the world’s seas were analyzed in order to assess the actual diversity of this important diatom family. A significant level of intraspecific variability was detected while the distribution of species and populations at spatial and temporal scale supported the functional differences among them that account for their distinct seasonality and their adaptation to different environmental conditions.

The number and abundance of diatom species in environmental samples are counted traditionally by means of light microscopy (LM). However, recognizing –let alone, counting- species is often challenging because of the existence of cryptic species and intraspecific phenotypic plasticity. Proper characterization requires isolation of cells, growing them into monoclonal cultures, and characterizing the cultures genetically and morphologically. However, not all species grow in culture, featureless ones are less likely to be isolated, and the procedure is laborious. High-throughput sequencing (HTS) metabarcoding bypasses morphology; DNA is collected from environmental samples, a particular marker sequenced, and the resulting sequences sorted into clusters or terminal clades assumed to represent species. Yet, reference barcodes of taxonomically validated species are needed to identify these clades. This exercise is the main aim of my thesis. Since it is impossible to do this for all the diversity within a PhD thesis project, we selected Chaetocerotaceae, an abundant and diverse family of marine planktonic diatoms, containing two genera: <i>Chaetoceros</i> and <i>Bacteriastrum</i>. Its members uniquely share setae; thin siliceous tubes emerging from the valve corners, facilitating detection in samples. Strains were obtained from the Gulf of Naples (GoN), from Central Chile and Roscoff – at sites for which LTER time series data are available. A total of 270 strains were obtained from these sites, and their 18S- and partial 28S rDNA sequences and morphological information gathered. The strains grouped into 60 genetically distinct species, thus providing a dataset of validated Chaetocerotacean 18S reference barcodes. Inferred molecular phylogenies showed monophyletic Chaetocerotaceae as well as monophyletic <i>Bacteriastrum</i> inside paraphyletic <i>Chaetoceros</i>, and the presence of cryptic diversity. To start with taxonomic updates, the species <i>C. sporotruncatus</i> and <i>C. dichatoensis</i> were described within the <i>C. socialis</i> species-complex based on spore morphology and sequence differences. Several rDNA sequences contained spliceosomal introns (ca. 100bp) and/or group-I introns (ca. 400bp). Phylogenies inferred from the introns did not corroborate rDNA phylogenies, suggesting horizontal gene transfer. Presence/absence of introns in conspecific strains sampled in different seasons suggests population differentiation between these seasons. A HTS dataset consisting of V4-sequences (part of 18S) from 48 seawater samples taken over the seasons in the GoN revealed 76 terminal clades of which 46 grouped with a reference barcode. Some of these species occur year-round whereas most others are seasonal. Surprisingly, of the 30 clades belonging to unknown Chaetocerotacean species, two appear to be among the most abundant in the GoN.

Diatoms are among the most productive photoautotrophic organisms on Earth. Within the diatom genus Leptocylindrus, two species, L. danicus and L. minimus, are reported as abundant in coastal waters worldwide and in the Gulf of Naples (GoN). This thesis aimed at a closer characterisation of Leptocylindrus species through different approaches, including the study of their morphology, molecular phylogeny, metagenomics and biochemistry. Eighty-three strains from the GoN and one strain (CCMP 1856) from the Atlantic US coast were analysed. Based on the morphological, molecular and life cycle differences, the taxonomy of the genus was revised. The GoN species previously identified as L. minimus was in fact identified as L. belgicus Meunier and was placed in a new genus, Tenuicylindrus Nanjappa and Zingone which, along with Leptocylindrus Cleve, belongs to the family Leptocylindraceae. Five species in all were included in the genus Leptocylindrus: L. danicus Cleve and L. minimus Gran, two novel species L. hargravesii and L. convexus, and L. aporus (Hargraves) Nanjappa & Zingone, which was raised from the variety to the species status. The real Leptocylindrus minimus was not found in the GoN. To address the distribution of the 6 species outside the GoN, two metagenomic databases, BioMarKs (Europe) and Tara Oceans (worldwide) were explored. Sequences of L. aporus, L. convexus and L. danicus were recovered at many sites in European waters and across the world's seas, while those of L. minimus were retrieved only in the Oslo fjord and those of T. belgicus were only found in the GoN and Oslo fjord. Additional diversity was observed in the Tara Oceans dataset but, in lack of morphological information, whether this diversity is real remains to be clarified. All species except L. minimus were also categorised based on the diversity in their oxylipins pathways. Leptocylindrus danicus and L. hargravesii shared common lipoxygenase pathways, different from the ones shared by the species L. aporus and L. convexus. Tenuicylindrus belgicus exhibits a pathway distinct from that of Leptocylindrus species. Species-specific compounds produced in minor quantities were also observed. Physiological experiments show that L. aporus can withstand higher (26 "C) temperature but not lower (12 CC) temperature, while L. danicus can withstand low temperature but not high temperature. This corresponds to the species occurrence in the natural environment, where L. aporus blooms during summer and L. danicus is found in all seasons except summer. Altogether, through an interdisciplinary approach, the studies described in this thesis provide substantial information that may have important implications in the field of ecology, evolution, conservation biology and biotechnology.

Aquesta tesi tracta la jerarquia i l'heterogeneïtat dels sistemes fluvials que afecten l'estructura de les comunitats bentòniques de diatomees. A nivell regional, es van buscar diferents grups de punts i les seves espècies indicadores, es va estudiar la resposta de les comunitats de diatomees als gradients ambientals, es va avaluar la utilitat de diferents índexs de diatomees i es va buscar el millor sistema de classificació per a condicions de referència. A nivell de conca, es volien definir els factors que determinen la distribució longitudinal de la diversitat de les comunitats de diatomees. Finalment, a nivell d'hàbitat es van determinar quins factors afecten les algues i els cianobacteris a aquesta escala i es va examinar la contribució relativa de l'ambient i l'espai en la distribució de la biomassa i composició d'algues i cianobacteris. Per tant, els diferents capítols d'aquesta tesi han estat desenvolupats seguint aquest esquema.<br>This thesis deals with the hierarchy and heterogeneity of stream systems affecting the structure of benthic diatom communities. At a regional level, I search for different groups of sites and their indicator taxa, I studied the responses of the diatom communities to the gradients of environmental variables, I tested the usefulness of diatom indices and I searched for the best classification system for reference conditions. At a watershed level my interest was to define the factors that determined the longitudinal distribution of diversity of diatom communities. Finally, at a habitat level it was interesting to determine the factors affecting algae and cyanobacteria at this scale and examine the relative effects of environmental factors and space on the distribution of biomass and composition of benthic algae and cyanobacteria. Thus, the different chapters of the thesis had been approached following this scheme.

Diatoms associated with foraminifers of the genus Amphistegina were assessed using a combination of morphological and molecular techniques. These included: 1) microscopic identification of diatoms cultured from the host, 2) sequencing of portions of the small subunit of the ribosomal RNA gene (18S) and the large subunit of the ribulose-1,5-bisphosphate carboxylase/oxygenase [i.e., RubisCO] gene (rbcL) from DNA extracted directly from the Amphistegina hosts and also from diatoms cultured from these hosts, and 3) denaturing gradient gel electrophoresis (DGGE) profiles of rbcL and internal transcribed spacer 1 (ITS1) PCR amplicons from DNA extracted directly from hosts and from cultures. Consistent with previous culture studies, multiple species of pennate diatoms of the genera Nitzschia, Fragilaria (including Nanofrustulum), Amphora, and Navicula, were cultured from >900 host specimens collected from >20 sites in the western Atlantic and four sites in the Pacific. Diatoms of the genus Nitzschia grew in about half of all successful cultures. The genetic identities of selected cultures were consistent with those based on morphological taxonomy. Diatom sequences from DNA extracted directly from the cytoplasm of the Amphistegina hosts were species specific and distinct from sequences obtained from cultured diatoms and from sequences in GenBank of diatom taxa previously reported as endosymbionts. Multiple phylogenetic analyses revealed that the 18S and rbcL diatom sequences from specimens of A. gibbosa collected from the Atlantic sites and of Amphistegina spp. from Hawai’i were most similar to the 18S and rbcL sequences of an unnamed Fragilariaceae diatom in GenBank (Accession # JX413542.1 for 18S and JX413559.1 for rbcL) and other closely related diatoms in that family. Of diatom taxa previously reported as endosymbionts of larger foraminifers, Nanofrustulum shiloi was the most similar, but not identical, to the sequences from hosts collected from the Atlantic and Hawai’i. The 18S and rbcL diatom sequences from the Atlantic host species, A. gibbosa, were all nearly identical, but small intra-species differences (subclades) were observed from specimens collected from the deepest (75 m) site in the Florida Keys and also from the eastern-most site, Young Island near St. Vincent. The 18S and rbcL diatom sequences from the two host species from Hawai’i, A. lobifera and A. lessonii, were more variable but still within the family Fragilariaceae. The diatom sequences from A. radiata collected from two sites in Papua New Guinea (PNG) were most similar to diatoms of the family Plagiogrammaceae and therefore distinct from sequences obtained from other Amphistegina species in this study, as well as from all diatoms previously reported as endosymbionts. A small difference was observed between the diatom sequences from host specimens collected from a Pacific site as compared to a Bismarck Sea site. The ITS1 DGGE profiles of DNA extracted directly from A. gibbosa specimens at different depths, locations, and seasons in the western Atlantic were nearly identical. Differences were seen between rbcL DGGE profiles of DNA extracted directly from the different Amphistegina host species. The rbcL DGGE profiles directly from all hosts were clearly different from those extracted from diatoms cultured from the same host specimens, as well as from Nitzschia laevis, a commonly reported diatom endosymbiont in past culture-based studies. My findings are consistent with ultrastructural studies of endosymbionts of Amphistegina published in the early 1980s and congruent with recent molecular studies of endosymbionts in other diatom-bearing foraminifers, all of which indicate specificity. Nevertheless, the consistency with which several diatom taxa have been reported in culture studies from all oceans indicates the possibility of some relationship with Amphistegina spp., either as important food items, epiphytes, or minor opportunistic symbionts that can thrive in culture media.

L’interaction entre les micro-organismes a de profondes répercussions sur les cycles biogéochimiques de l’océan. Cependant, la question de savoir comment les microbes s’associent les uns aux autres aux échelles spatiale et temporelle et si les associations de diatom-procaryote et de DOM-procaryote affectent la distribution de ces trois composants est ouverte. Au chapitre 1, nous observons des compositions distinctes de diatomées et de communautés procaryotes parmi les principales zones océaniques. Des relations significatives entre les changements de composition des diatomées et des procaryotes ont été trouvées. Au chapitre 2, nous avons observé deux proliférations consécutives de phytoplancton, chacune composée d’assemblages de diatomées distincts. À l’aide d’une analyse de réseau, nous avons identifié deux groupes de diatomées ayant eu des modèles de corrélation avec des taxa procaryotes. Au chapitre 3, nous avons trouvé la composition distincte de la MOM et celle des procaryotes totaux et actifs sur et hors du plateau. Les corrélations DOM-procaryotes étaient plus fortes sur le plateau que sur le plateau. Les principaux groupes de procaryotes actifs fortement corrélés à la MOM étaient qualitativement similaires dans les deux écosystèmes et quantitativement plus élevés sur le plateau. Pris ensemble, nos résultats démontrent les associations significatives entre les diatomées et les procaryotes, et entre les procaryotes et les DOM. Les compositions des communautés procaryotes sont influencées à la fois par les diatomées et les DOM<br>The interplay among microorganisms profoundly impacts biogeochemical cycles in the ocean. However, the questions of how microbes associated with each other on the spatial and temporal scale, and whether the associations of diatom-prokaryote and of DOM-prokaryote affect the distributions of these three components are open. In chapter 1, we observed distinct compositions of diatom and prokaryotic communities among the major ocean zones. Significant relationships between compositional changes of diatoms and of prokaryotes were found. In chapter 2, we observed two consecutive phytoplankton blooms, each composed of distinct diatom assemblages. Using network analysis, we identified two groups of diatoms representative of the spring and summer bloom, respectively, that had opposite correlation patterns with prokaryotic taxa. In chapter 3, we found the distinct composition of DOM and that of total and active prokaryotes on and off the plateau. The DOM-prokaryote correlations were overall stronger on the plateau than that off the plateau. The key active prokaryotic groups that strongly correlated with DOM were qualitatively similar in both ecosystems and quantitatively higher on the plateau. Taken together, our results demonstrate the significant associations between diatoms and prokaryotes, and between prokaryotes and DOM. The compositions of prokaryotic communities are influenced by both diatoms and DOM

Diatoms have been proven to be reliable indicators of water quality in many countries of the world particularly Europe. The potential use of diatoms as indicators of water quality in South Africa was tested in the studies in this document. This study evaluates the potential use of diatom based indices by testing it against a macroinvertebrate index (SASS 5) and evaluating the variation in the index scores of the two indices due to changes in chemical water quality and habitat. It was concluded that the diatom monitoring system performs well as bioindicator of water quality. It was also concluded that it should be used as a complementary system to the much used SASS 5 invertebrate index. This conclusion was made due to the fact that diatoms react more directly to changes in water quality than macroinvertebrates (SASS 5), and macroinvertebrates react more readily to changes in habitat than diatoms. A further part of the study was to assess whether aut-ecological or diversity based diatom indices performed best in South African conditions. This study found that the ecological indices were more sensitive to changes in water quality than the diversity indices. The diatom based indices that performed best as water quality indicators were the specific pollution sensitivity index (SPI) and the biological diatom index (BDI). A standard method for the sampling, preparation and enumeration for diatoms to be used for index score generation is also suggested to ensure the comparability of diatom based index data to facilitate use of such bio monitoring data for management purposes. The main focus of the study was to eliminate some of the obstacles for the use of diatoms as bio indicators of water quality in South Africa. It is believe that this aim has been accomplished in the study.<br>Thesis (Ph.D. (Environmental Science))--North-West University, Potchefstroom Campus, 2008.

Domoic acid (DA), a potent neurotoxin that has the potential to cause amnesic shellfish poisoning (ASP), is produced by members of the marine diatom genus Pseudo-nitzschia. Outbreaks of ASP in humans and of DA poisoning in birds and marine mammals have been reported across the United States and Canada since the late 1980's. Pseudo-nitzschia species can be extremely abundant in Florida waters, with densities often exceeding 106 cells/L, and sometimes exceeding 107 cells/L. Based on preliminary data, it is evident that at least nine species of Pseudo-nitzschia are found in Florida coastal waters. At least six of these species are known to produce DA in other parts of the world, and some are morphologically identical to some of the major toxin-producing species in Californian and Canadian waters. Despite the strong presence of Pseudo-nitzschia, there has never been a report of ASP or a DA-related animal mortality event from Florida. Data collected from 2004 to 2011 show maximum Pseudo-nitzschia abundances exceeded 4 x 107 cells/L. Six species of Pseudo-nitzschia were identified from central west and southwest Florida waters via light and electron microscopy. This is the first report of P. micropora from the Gulf of Mexico. Additionally P. calliantha, P. cuspidata, and P. pungens were identified as producers of DA in Florida coastal waters; although cell quotas of DA were low. Low levels of DA were detected in about one third of the water samples analyzed and DA concentrations measured in the majority of shellfish from the study area were at least an order of magnitude below the regulatory limit of 20 µg/g, suggesting that Pseudo-nitzschia currently poses little threat to human health in Florida. However, DA production in Pseudo-nitzschia species has been shown to be variable and dependent on nutrient conditions, indicating that the potential for DA-related events to occur in Florida warrants further investigation.

Thesis (M.S.)--Kutztown University.<br>Source: Masters Abstracts International, Volume: 45-06, page: 3039. Typescript. Abstract precedes thesis as preliminary leaves [1-4]. Includes bibliographical references (leaves [51-52]).

Benthic diatoms, photoautotrophic, silicate plated, single-celled aquatic organisms dwelling on substrates, have been used in bioindication, since they are good indicators of ecological water state. In this thesis, we have used a multi-scalar approach to observe how diatoms from Spanish Mediterranean rivers are affected by the characteristics of the habitats they live in. These organisms were observed under a taxonomic-indicative, functional-grouped and morphometric prism. The samples stem from Mediterranean rivers pertaining to either the Ebro Basin, or jurisdictions of the Catalan rivers or the Júcar authorities. Ebro samples have a fundamental importance, due to their temporal frame of 10 years, which has permitted the establishment and observation of changes in diatom communities and their characteristics. Two experimental setups, comparing differing water compositions and hydrological characteristics, were made in the other basins. The structure of this thesis takes a gradual decrease in observation range. The macro-scale: chapter studied benthic diatom communities from the Ebro River Basin taxonomically, based on samplings ranging 10 years. We studied if diatom communities were maintained in time, or what parameters could help to the establishment of ecoregions. This study showed that the ecotype division of rivers established by the Water Framework Directive (WFD) did not reflect diatom assemblages well. A double approach of physico- chemical and diatom-sociological aggregation can create a better mirror of diatom communities, thus improving ecoregions for diatoms. The meso-scale chapter investigated the Segre, Ebro tributary, observing the relationship between land use and diatom assemblages and indicator values. Land uses have a direct effect on river water composition. Thus, a link between upstream land cover and diatom assemblages was expected. The results show that only the predominant covers affect both the composition of the diatom community and indicator values. Structural Equation Modelling comparisons have established changes in the importance of physicochemical parameters through time and depending on diatom community structure. Diversity indices and bioindicator values were affected mostly by physicochemical composition, and tangentially by land cover. In the micro-scale chapter, the reaction of diatoms at each site was studied. To do this, we parted the chapter in three sections, two life form experiments to observe how physicochemical composition and hydrology affect life forms, and how morphometry can be affected through abiotic parameter variation in time. The first, made in the Llobregat Basin, was an experimental approach to ascertain the effect of intrinsically different sites on diatom life forms and ecological guilds and the change when these communities are translocated. This showed that, although the physicochemical parameters seemed to favour functional groups, changing the community into a different site could still maintain some of the characteristic life forms. Then, a comparison of functional structure of the diatom community in temporary rivers (that lose part or the totality of its surface water) of Mediterranean basins along the northeast coast was made. It showed that the hydrological regime (connectedness of the stream in total) had a bigger impact than aquatic state (water quantity present at time of sampling). The disconnection of streams also affected the use of conventional diatom bioindicators that will be addressed in the future. Finally, in this microscale prism, we automatically photographed samples from the Ebro River to extract diatom morphometry features. Relating these to physicochemical parameters of each site and their temporal variability, we saw that diatom sizes are affected by water composition. The surface-to-volume ratio (S/V) was highly correlated. An up to now neglected parameter, diatom width, was highly affected by physicochemical parameters. This thesis attempted to establish how diatoms and their traits are affected by their surroundings, observing the effect of abiotic parameters, such as physicochemical composition, land use, and substrate characteristics.<br>Las diatomeas bentónicas son organismos fotoautotróficos unicelulares, acuáticos y colonizadores de sustratos, que se han usado en bioindicación por ser buenas indicadoras del estado ecológico del agua. En esta tesis hemos estudiado cómo las diatomeas de ríos ibéricos mediterráneos se ven afectadas por la ecología del medio donde habitan, a diversas escalas. Estos organismos se estudiaron a nivel taxonómico e indicativo, funcional y morfométrico. La estructura de esta tesis sigue una aproximación a la reducción de escala de trabajo. El capítulo de macro-escala se basó en una investigación de las comunidades bentónicas epilíticas de las diatomeas del río Ebro, en base a muestreos realizados a lo largo de 10 años. Este estudio se ha demostrado que la división en ecotipos fluviales establecida para el seguimiento de la Directiva Marco del Agua (DMA) no coincide con la diversificación delascomunidades deestosorganismos. Nuestrosresultados apuntanqueunaaproximacióndoble (composición físico-química y estructura de la comunidad) puede reflejar mejor la realidad para las diatomeas. En el capítulo de meso-escala se investigó el río Segre con la finalidad de establecer las relaciones entre los usos del suelo y las comunidades de diatomeas y valores de los índices de diatomeas. Los usos del suelo afectan directamente a la composición del agua fluvial. Por ello, se esperaba una correlación entre el uso del suelo aguas arriba de las comunidadesde diatomeas estudiadas. Los resultados muestranque únicamentelos usos mayoritarios afectan la composición las comunidades de diatomeas y los valores de los índices diatómicos. En el capítulo de microescala se estudió la reacción de las diatomeas en cada punto. Para ello el capítulo se dividió en tres secciones. Un experimento observó el efecto de puntos intrínsecamente diferenciales sobre las formas de vida, y cambios de estas tras su translocación. La otra sección comparó la composición funcional de la comunidad de diatomeas en ríos temporales, que sufren pérdida parcial o total del agua superficial. Finalmente, aún en microescala, se fotografiaron automáticamente muestras de diatomeas del río Ebro para calcular sus características morfométricas. Estas se relacionaron con los parámetros fisicoquímicos de cada punto y con su variabilidad temporal. El resultado fue una clara afectación de tamaños valvares según la composición del agua. La relación superficie-volumen estaba altamente correlacionada y la anchura valvar, obviada hasta ahora, se vio afectada por los parámetros fisicoquímicos.<br>Les diatomees bentòniques, organismes fotoautotròfics unicel·lulars, aquàtics i colonitzadors de substrats, que s’han utilitzat a la bioindicació per ser bones indicadores del estat ecològic de l’aigua. En aquesta tesi hem estudiat com les diatomees de rius ibèrics mediterranis es veuen afectades per l’ecologia del medi al que habiten a diverses escales. Aquests organismes es varen observar a nivell taxonòmic-indicatiu, funcional i morfomètric. L’estructura d’aquesta tesi segueix una aproximació a la reducció d’escala de treball. El capítol de macro-escala es basà en una investigació taxonòmica de les comunitats bentòniques epilítiques de diatomees del riu Ebre, basat en mostrejos realitzats al llarg de 10 anys. Aquest estudi ha mostrat que la divisió d’ecotips fluvials establerta per a el seguiment de la Directiva Marc de l’Aigua (DMA) no coincideix amb la diversificació de les comunitats d’aquests organismes. Els resultats assenyalen que una aproximació doble (composició fisicoquímica i estructura comunitària) podria reflectir millor la realitat per a les diatomees. Al capítol de meso-escala s’estudià el Segre per tal d’establir les relacions entre els usos del sòl, les comunitats de diatomees i els seus valors indicadors. Els usos del sòl afecten directament a la composició de l’aigua fluvial. Per això, s’esperava una correlació entre els usos del sòl aigües amunt de les comunitats de diatomees estudiades. Els resultats mostren que únicament els usos majoritaris afecten els la composició de les comunitats de diatomees els i valors dels índexs diatòmics. El capítol de micro-escala investigà la reacció de les diatomees a cada punt. Per això, el capítol es dividí en tres seccions. Un experiment observà l’efecte de punts intrínsecament diferencials sobre les formes de vida i canvis d’aquests després de la translocació. L’altra secció comparà la composició funcional de la comunitat de diatomees a rius temporals, que pateixen la pèrdua total o parcial de l’aigua superficial. Finalment, seguint a la micro-escala, es fotografiaren les mostres del riu Ebre automàticament per calcular les seves característiques morfomètriques. Aquestes es relacionaren amb els paràmetres fisicoquímics de cada punt i la seva variabilitat temporal. El resultat fou una clara afectació de mides valvars segons la composició de l’aigua. La relació superfície-volum estava altament correlacionada amb les variacions fisicoquímiques i l’amplada valvar, obviada fins ara, era afectada pels paràmetres fisicoquímics.

<p>Benthic diatoms are valuable tools for biological monitoring and paleo-ecological reconstruction of past environmental conditions. This thesis aims at describing size-related properties of benthic diatoms and suggests that data assessment for community analysis can be improved by considering the importance of scale. It investigates which environmental factors structure epilithic diatom communities on the coast of the Gulf of Bothnia and identifies environmental factors correlated with phytobenthic biomass. It also contributes to the floristic knowledge of the Baltic Sea. </p><p>Diatom species show large variation in size. The responses of large species (≥1000 μm3) in diatom communities to environmental factors are underestimated if solely measured as relative abundance, as is the common practice. However, relative abundance gives the best gradient resolution, as compared to surface area and biovolume, if species are counted separately in two biovolume classes. Small and large species in the same community may respond differently to the same environmental factors. </p><p>To assess the principal environmental factors structuring diatom communities in the Gulf of Bothnia, 270 quantitative samples were collected from submerged stones. Sampling was carried out in spring in four areas of the Bothnian Bay, characterized by a stable north-south salinity gradient (0.4-3.3 psu), and in three areas of the Bothnian Sea which has a rather uniform salinity of ca. 5 psu. Canonical correspondence analysis (CCA) identified salinity and exposure to wave action as the principal factors structuring the diatom communities of the Bothnian Bay, whereas exposure to wave action was the principal factor in the Bothnian Sea. Measurements of relative ignition loss suggested that the cover of macroalgae, and thereby the higher abundance of epiphytic diatoms in the epilithic samples, was positively correlated with salinity in the Bothnian Bay and with water movement in the Bothnian Sea. </p><p>Two new brackish water species are described, <i>Navicula sjoersii</i> S. Busse & Snoeijs and <i>N. bossvikensis</i> S. Busse & Snoeijs. The new species are compared with <i>N. perminuta</i> Grunow, a common brackish-water species.</p>

Les diatomées forment un groupe important d’algues brunes microscopiques colonisant l’ensemble des milieux aquatiques. Organismes photosynthétiques possédant un exosquelette siliceux, elles sont reconnues depuis plusieurs décennies comme d’excellents bio-indicateurs des caractéristiques physico-chimiques de l’eau. Cette bio-indication repose sur la connaissance de l’écologie des espèces. Peu de travaux ont été conduit dans le Sahel et en particulier au Tchad, alors qu’il possède l’un des plus grands lacs d’eau douce d’Afrique, le lac Tchad. A partir d’une étude exhaustive menée dans tous les lacs tchadiens, Tchad, Iro, Fitri et d’Ounianga (à l’exception du lac Léré inaccessible pour des raisons de sécurité), l’inventaire des diatomées est dressé. La distribution des diatomées en fonction des caractéristiques hydrochimiques de l’eau est explorée et une modélisation est proposée afin de quantifier les paramètres de l’environnement aquatique à partir de l’étude des diatomées fossiles<br>Diatoms form a large group of microscopic brown algae colonizing all aquatic environments. Photosynthetic organisms with siliceous exoskeletons have been recognized and used for decades as excellent bio-indicators of the water chemistry. This bio-indication is based on knowledge of the self-ecology of the species. Little work has been carried out in the Sahel and especially in Chad, while it has one of the largest freshwater lakes in Africa, Lake Chad. Based on a comprehensive study carried out in all Chadian lakes, Chad, Iro, Fitri and Ounianga (with the exception of Lake Léré due to safety reasons), the diatom inventory is drawn up. Diatomaceous distributions based on water hydrochemical characteristics are explored and modeling is proposed to quantify aquatic environmental parameters from the fossil diatom study

Il genere Pseudo-nitzschia, spesso presente nei popolamenti fitoplanctonici nel Golfo di Trieste, comprende alcune specie potenzialmente tossiche, produttrici di acido domoico, una neurotossina che provoca nell’uomo la Sindrome Amnesica per ingestione di bivalvi. Per questo motivo un’identificazione tassonomica è necessaria fino a livello specifico. Pertanto, lo studio intrapreso si è focalizzato su: -identificazione a livello di specie, tramite microscopia elettronica a trasmissione (TEM), di ceppi di Pseudo-nitzschia isolati dal Golfo di Trieste; -caratterizzazione genetica grazie al DNA-barcoding utilizzando il marcatore ITS2; -analisi tossicologica per l’identificazione dell’acido domoico tramite il metodo della cromotografia liquida associata alla spettrometria di massa in tandem; -analisi di dati abiotici e biotici raccolti dal 2010 al 2016 in una stazione di ricerca a lungo termine nel Golfo di Trieste. Sono stati isolati 15 ceppi assegnati, da osservazioni al TEM e analisi genetiche, a tre specie: P. mannii, P. calliantha, P. subfraudulenta. Sebbene le ultime due in altri studi siano state riportate tossiche, nessuno dei ceppi isolati dal Golfo di Trieste è risultato produrre tossine. L’analisi della serie temporale 2010-2016 mostrava una variabilità interannuale del genere con un ciclo stagionale medio caratterizzato da 3 picchi: primaverile, estivo e autunnale; ciò potrebbe indicare che vi siano diverse specie con diversi periodi di fioritura. Infatti, l’osservazione al TEM di campioni naturali ha evidenziato la presenza di altre specie: P. cf delicatissima, P. cf pseudodelicatissima, P. pungens e P. fraudulenta, tutte potenzialmente tossiche. Per avere un quadro completo delle specie presenti e descriverne il ciclo stagionale, sarebbe necessario isolare un maggior numero di ceppi in differenti periodi dell’anno e testare la produzione di tossine in diverse condizioni di coltura per valutare il potenziale tossico di tali ceppi in differenti condizioni ambientali.

Les bactéries et microalgues marines sont acteurs clés du fonctionnement des écosystèmes océaniques et leur contribution dans les cycles biogéochimiques majeurs est largement reconnue. Dans ce contexte, il apparaît essentiel de mieux comprendre les interactions existant entre bactéries et microalgues. Dans l’environnement marin, les interactions spécifiques entre microorganismes nécessitent une forte proximité qui n’est souvent rendue possible que par un attachement cellulaire. La première partie de ce travail de thèse a consisté à sélectionner les microalgues qui présentaient des bactéries physiquement attachées. Deux diatomées appartenant aux genres Thalassiosira et Chaeoceros ont été retenues afin d’étudier leur microflore épibionte issue d’associations à long terme (culture de microalgues établies depuis plusieurs années) et à court terme (microalgues prélevées directement dans l’environnement). Ces travaux ont permis de mettre en évidence une forte ressemblance des communautés épibiontes dans les associations à long terme, qui s’opposait à la forte différence des épibiontes issus des associations à court terme. Les communautés d’épibiontes bactériens étaient majoritairement composées d’alpha- et gammaprotéobactéries, mais aussi de Bacteroidetes et d’actinobactéries. Cette étude a également permis de mettre en évidence que la surface des microalgues représentait un écosystème particulier puisque près de la moitié des épibiontes isolés correspondaient à de nouveaux taxons (genres et espèces). Une de ces souches qui constitue un nouveau genre a été complètement caractérisée, contribuant à l’enrichissement de la diversité bactérienne décrite. Enfin, la nature des interactions entre les deux diatomées et leurs bactéries épibiontes a été analysée par l’intermédiaire de co-cultures, afin d’identifier une interaction forte, qui pourra être examinée par transcriptomique. De très nombreuses interactions commensalismes ont été mises en évidence, reflet de la reminéralisation de la matière organique par les bactéries. Cependant, un faible impact des bactéries sur la croissance des microalgues a été observé. Les conditions expérimentales qui excluent au maximum les stress abiotiques et biotiques, masquent peut-être les interactions qui pourraient se produire dans un environnement naturel plus fluctuant. Ces résultats témoignent de la complexité des interactions biotiques, fournissent des méthodes et des organismes modèles permettant de les étudier et soulèvent de nombreuses hypothèses exaltantes pour les travaux futurs<br>Marine microalgal and bacterial contribution to the global biogeochemical cycles is largely recognized and lead to define them as key actors of oceanic ecosystems. In this context, it is essential to better understand the interactions occurring between bacteria and microalgae. In the marine environment, specific interactions between microorganisms require tight physical association that is made possible by cellular attachment. In this work, we first selected microalgae with physically attached bacteria. Two diatoms belonging to the genus Thalassiosira and Chaetoceros were selected to study the epibiotic microflora from long-term (microalgae in culture) and short-term (microalgae directly collected from natural communities) associations. This work highlighted strong similarities between epibiotic assemblages from long-term associations and a higher difference for epibiotic communities from short-term associations. The bacterial epibiotic assemblages were mainly composed of Alpha- and Gammaproteobacteria but also Bacteroidetes and Actinobacteria. This study also highlighted that the surface of microalgae represented a peculiar ecosystem where nearly half isolates constituted new taxa (genera and species). One of them representing a new genus has been completely characterized, contributing to the enrichment of the described bacterial diversity. Finally, the nature of interactions between diatoms and their epibiotic bacteria was analyzed by co-culturing to identify strong interactions, to be further examined by transcriptomics. Numerous commensal interactions have been identified, corresponding to the bacterial remineralization of organic matter. However, only small effects of bacteria on microalgal growth were observed. The experimental conditions that exclude a maximum of abiotic and biotic stresses may mask potential interactions that could occur in an unstable natural environment. These results reflect the complexity of biotic interactions, provide methods and model organisms to study them, and raise many exciting hypotheses for future work

Les diatomées constituent un groupe majeur du phytoplancton marin. Ces microalgues peuvent former des blooms saisonniers considérables ayant des implications biogéochimiques importantes notamment sur l’export de carbone. A ce jour, la manière dont le parasitisme structure leur développement reste élusive. L’objectif de cette thèse était d’identifier le(s) parasite(s) associé(s) aux diatomées prédominantes en Manche Occidentale afin de mieux comprendre comment le parasitisme contrôle les blooms de ces microalgues. La première partie de cette thèse visait à décrire le réseau de parasites qui régule les diatomées du genre Guinardia, taxon-clef du microphytoplancton en Nord-Atlantique. Pour cela un travail d’isolement intensif des espèces de Guinardia et des parasites associés a été réalisé entre Août 2015 et Octobre 2016 à la station d’échantillonnage à long terme SOMLIT-Astan. La caractérisation des isolats a permis de mettre en évidence une diversité insoupçonnée de parasites régulant Guinardia delicatula, avec au minimum trois types de parasites appartenant à des lignées distinctes : des virus (Picornavirales, Bacillarnavirus), un parasite eucaryote (Labyrinthulomycetes, Aplanochytrium sp.) et des bactéries algicides (Bacteroidetes, Kordia sp.). Ces nouveaux parasites n’ont jamais été décrits en association avec Guinardia et s’ajoutent donc aux autres parasites connus pour cet hôte. Les parasites isolés à SOMLIT-Astan présentent des stratégies d’infections différentes, suggérant des interactions complexes dans la nature. Dans un second temps, nous avons étendu notre étude à des nanodiatomées appartenant aux genres Minidiscus et Thalassiosira, largement distribuées dans l’océan global mais dont les dynamiques saisonnières et leur contrôle sont quasi-inexplorées. La combinaison d’outils microscopiques et moléculaires a mis en évidence que ces nanodiatomées dominent numériquement la communauté phytoplanctonique à SOMLIT-Astan et qu’elles présentent des patrons saisonniers très marqués. La collection importante de 82 parasites, dont 27 virus, isolés tout au long de l’année à partir de ces deux genres indique pour la première fois un rôle-clé des interactions biotiques dans la régulation des dynamiques des nanodiatomées. Ce projet de thèse révèle une diversité nouvelle et importante de parasites associés aux diatomées au Manche Occidentale. La contribution relative de ces parasites dans la régulation des diatomées, leurs implications biogéochimiques, et évolutives reste à mettre en lumière<br>Diatoms are one of the most successful phytoplankton groups. They can form considerable seasonal blooms with important biogeochemical implications, especially with respect to carbon export. To date, the role of parasites in the regulation of diatom blooms remains elusive. The main objective of this thesis was to identify the parasites associated to dominant diatom species in the Western English Channel to better understand how parasitism regulates diatom blooms. The first part of the project aimed to identify parasitic network that controls the diatom Guinardia, a major component of microphytoplankton communities in coastal systems of the North Atlantic. Intensive isolation of Guinardia species and associated parasites into laboratory culture was carried out between August 2015 and October 2016 from the SOMLIT-Astan long- term monitoring station. Characterization of these isolates revealed an unsuspected diversity of parasites that infect Guinardia delicatula, with at least three types of parasites belonging to distinct lineages: viruses (Picornavirales, Bacillarnavirus), a eukaryotic parasite (Labyrinthulomycetes, Aplanochytrium sp.) and algicidal bacteria (Bacteroidetes, Kordia sp.). These pathogens have never previously been described in association with Guinardia and therefore add to the list of known parasites reported for this host species. The parasites isolated from SOMLIT-Astan displayed different infection strategies, suggesting complex interplays in nature. In the second part of this thesis, the study was extended to nanoplanktonic diatoms that belong to the genera Minidiscus and Thalassiosira. These minute microalgae are widespread in the global ocean, but their seasonal dynamics are quasi-unexplored. Using a combination of microscope observations and molecular tools, we showed that these nanodiatoms numerically dominated the phytoplankton community at the SOMLIT-Astan station and that they have contrasted seasonal patterns. The large set of 82 parasites, including 27 viruses, isolated from these two genera throughout the sampling period highlights, for the first time, the key role of biotic interactions in the regulation of nanodiatom dynamics. This Ph.D. project has revealed significant novel diversity of pathogens of diatoms in the Western English Channel. The relative contribution of these parasites to regulation of diatom populations and their resulting biogeochemical and evolutionary implications remain to be investigated

Les bactéries et microalgues marines sont acteurs clés du fonctionnement des écosystèmes océaniques et leur contribution dans les cycles biogéochimiques majeurs est largement reconnue. Dans ce contexte, il apparaît essentiel de mieux comprendre les interactions existant entre bactéries et microalgues. Dans l’environnement marin, les interactions spécifiques entre microorganismes nécessitent une forte proximité qui n’est souvent rendue possible que par un attachement cellulaire. La première partie de ce travail de thèse a consisté à sélectionner les microalgues qui présentaient des bactéries physiquement attachées. Deux diatomées appartenant aux genres Thalassiosira et Chaeoceros ont été retenues afin d’étudier leur microflore épibionte issue d’associations à long terme (culture de microalgues établies depuis plusieurs années) et à court terme (microalgues prélevées directement dans l’environnement). Ces travaux ont permis de mettre en évidence une forte ressemblance des communautés épibiontes dans les associations à long terme, qui s’opposait à la forte différence des épibiontes issus des associations à court terme. Les communautés d’épibiontes bactériens étaient majoritairement composées d’alpha- et gammaprotéobactéries, mais aussi de Bacteroidetes et d’actinobactéries. Cette étude a également permis de mettre en évidence que la surface des microalgues représentait un écosystème particulier puisque près de la moitié des épibiontes isolés correspondaient à de nouveaux taxons (genres et espèces). Une de ces souches qui constitue un nouveau genre a été complètement caractérisée, contribuant à l’enrichissement de la diversité bactérienne décrite. Enfin, la nature des interactions entre les deux diatomées et leurs bactéries épibiontes a été analysée par l’intermédiaire de co-cultures, afin d’identifier une interaction forte, qui pourra être examinée par transcriptomique. De très nombreuses interactions commensalismes ont été mises en évidence, reflet de la reminéralisation de la matière organique par les bactéries. Cependant, un faible impact des bactéries sur la croissance des microalgues a été observé. Les conditions expérimentales qui excluent au maximum les stress abiotiques et biotiques, masquent peut-être les interactions qui pourraient se produire dans un environnement naturel plus fluctuant. Ces résultats témoignent de la complexité des interactions biotiques, fournissent des méthodes et des organismes modèles permettant de les étudier et soulèvent de nombreuses hypothèses exaltantes pour les travaux futurs<br>Marine microalgal and bacterial contribution to the global biogeochemical cycles is largely recognized and lead to define them as key actors of oceanic ecosystems. In this context, it is essential to better understand the interactions occurring between bacteria and microalgae. In the marine environment, specific interactions between microorganisms require tight physical association that is made possible by cellular attachment. In this work, we first selected microalgae with physically attached bacteria. Two diatoms belonging to the genus Thalassiosira and Chaetoceros were selected to study the epibiotic microflora from long-term (microalgae in culture) and short-term (microalgae directly collected from natural communities) associations. This work highlighted strong similarities between epibiotic assemblages from long-term associations and a higher difference for epibiotic communities from short-term associations. The bacterial epibiotic assemblages were mainly composed of Alpha- and Gammaproteobacteria but also Bacteroidetes and Actinobacteria. This study also highlighted that the surface of microalgae represented a peculiar ecosystem where nearly half isolates constituted new taxa (genera and species). One of them representing a new genus has been completely characterized, contributing to the enrichment of the described bacterial diversity. Finally, the nature of interactions between diatoms and their epibiotic bacteria was analyzed by co-culturing to identify strong interactions, to be further examined by transcriptomics. Numerous commensal interactions have been identified, corresponding to the bacterial remineralization of organic matter. However, only small effects of bacteria on microalgal growth were observed. The experimental conditions that exclude a maximum of abiotic and biotic stresses may mask potential interactions that could occur in an unstable natural environment. These results reflect the complexity of biotic interactions, provide methods and model organisms to study them, and raise many exciting hypotheses for future work

Abstract Understanding of natural and human induced changes to freshwater biodiversity patterns is critical for efficiently conserving and managing these highly impacted ecosystems. In this doctoral thesis, I study the natural spatial and temporal variability of littoral macroinvertebrate communities, as well as aquatic biodiversity responses (of bryophytes, macroinvertebrates and diatoms) to human impact on forested headwater streams. I also study the temporal variability of natural and human-impacted stream communities. I show that littoral macroinvertebrate communities are most variable between individual samples and to some extent between littorals, and that the diversity patterns of rare and common littoral macroinvertebrates vary at different spatial scales. Temporal (interannual) variability is of minor importance, particularly for the core species of the community. For rare species, however, the temporal component was generally more important than spatial turnover. For headwater streams, I show that most taxonomic groups responded negatively to human impact on the adjacent riparian forest. Nevertheless, pristine riparian forest is not a sufficient surrogate for stream biodiversity as also streams with relatively disturbed riparian forests supported diverse benthic communities. A rapid classification method based on the physical structure of the stream channel and its riparian forest is able to identify the reference-state communities, as well as the most severely altered communities, but a reliable identification of the intermediately-disturbed sites would need more precise information about the key stressors of stream communities. I found that fine sediments originating from forest drainage were the main factor causing reduction of stream biodiversity. I also found that forestry impacted streams varied temporally more than pristine streams, emphasizing the importance of interannual sampling of impacted streams for a reliable status assessment<br>Tiivistelmä Luonnollisen ja ihmisen aiheuttaman biodiversiteettivaihtelun ymmärtäminen hoito- ja suojelutoimissa on tärkeää pienvesien monimuotoisuuden turvaamiseksi. Tarkastelen väitöskirjassani järvien rantavyöhykkeen pohjaeläinten ajallista ja paikallista vaihtelua sekä latvapurojen eliöyhteisöjen (pohjaeläimet, sammalet, piilevät) vasteita ihmisen aiheuttamaan fysikaaliseen muutokseen rantametsässä ja purouomassa. Tarkastelen myös ajallisen vaihtelun eroja luonnontilaisten ja ihmisvaikutteisten latvapurojen eliöyhteisöjen välillä. Osoitan, että järven rantavyöhykkeen pohjaeläinyhteisöt vaihtelevat eniten yksittäisten näytteiden välillä ja pienessä määrin eri rantojen välillä, mutta ajallinen vaihtelu ei heikennä tulosten luotettavuutta muiden kuin harvinaisten lajien osalta yhteen vuoteen rajoittuvassa näytteenotossa. Purotutkimuksissa osoitan, että useiden vesieliöryhmien lajirunsaus muuttuu ihmisen aiheuttaman rantametsän muutoksen seurauksena, mutta luonnontilaista rantametsää ei silti voida pitää yksiselitteisesti myös puron suojelutason mittarina, koska se ei välttämättä turvaa eliöiden lajistollista eheyttä suhteessa alkuperäiseen alueelliseen lajistoon. Rantametsän ja uoman fysikaalisiin rakennepiirteisiin perustuvaa nopeaa luokittelumenetelmää voidaan käyttää eliöyhteisöltään monimuotoisimpien ja metsätalouden voimakkaimmin rasittamien purojen tunnistamisessa. Eliöyhteisöltään lievemmin muutettujen purojen luotettavaan erotteluun luokittelun pitäisi kuitenkin sisältää tarkempaa tietoa metsäojitusten aiheuttamasta liettymisestä, joka on tulosteni perusteella haitallisin metsätaloudesta johtuva puroyhteisöjä rasittava tekijä. Havaitsin myös metsätalouden rasittamien purojen tilanarvioinnin toistettavuuden olevan luonnontilaisia puroja heikompaa, joten metsätalouden rasittamien purojen pidempiaikainen seuraaminen tuntuu välttämättömältä luotettavien tilanarvioiden tuottamiseksi

Der vorliegende Band wirft einen Blick in verschiedene Forschungsfelder, die an der Professur Interkulturelle Kommunikation der Technischen Universität Chemnitz in den letzten Jahren von Studierenden im Masterstudiengang ‚Interkulturelle Kommunikation – Interkulturelle Kompetenz‘ bearbeitet wurden. Die den sechs Artikeln zugrunde liegenden Studien nutzen Methoden der qualitativen Sozialforschung zur Datenerhebung und -auswertung. Die Artikel thematisieren interkulturelle Lernprozesse in internationalen Workcamps und interkulturellen Trainings, Erfahrungen während eines Auslandsstudiums und im interreligiösen Austausch sowie die Zusammenarbeit in multikulturellen Teams.<br>This volume gives insight into different research projects conducted by students in the master‘s programme ‚Intercultural Communication – Intercultural Competence‘ at the Chair of Intercultural Communication at Chemnitz University of Technology. All empirical studies on which the articles are based use methods of qualitative social research for data collection and analysis. The articles focus on intercultural learning processes in international workcamps and intercultural trainings, experiences during studies abroad and in interreligious dialogues as well as cooperation in multicultural teams.

The ongoing trend with urban infill often implicates a conflict with urban green areas, which becomes a problem when green areas in cities are declining and when biodiversity is threatened on a global scale. This case study investigates how green areas and existing biological values are prioritized in an area in Malmö where infill is taking place (Översiktsplan för del av Kirseberg). Specifically, planning process and dialogue, on detailed comprehensive planning level, between the municipality and the landowner is analysed and compared with the policy plan for the area. The methods used are semi-structured interviews combining qualitative and quantitative data.The results show that many of the planning policies regarding green areas are prioritized and considered. However, when it comes to preserving existing vegetation and biological values, these policy goals are prioritized lower than the other policies, which leads to postponed conservation measures. Arguments for planning green areas are about structural concerns and attractivity. Municipal planners are concerned about the low amount of green areas and they find that policies and the planning and building act for green areas give a poor support in the planning process.Vague policy goals for green areas make it difficult for planners to balance between the many policy goals they need to consider. Although the actors have common interests and two-sided compromises are done, profit and a high exploitation level are the priorities of the landowner,which leads to fewer green areas. Landownership therefore limits municipal influence to planfor public interests like green areas. Furthermore, the political focus on high exploitation is another reason for this. Insufficient and outdated policies and planning material are also concerns that affects the planning of green areas.Green areas and biological values are not prioritized enough on the detailed comprehensive planning level neither in the policies of the plan, in the planning process nor in other policies. To change this, both planning laws, policies and political will need to prioritize green areas higher. Many studies state that the planning and building act is insufficient for planning green areas that support ecosystem services on private properties. This seems to apply to this case study as well.

碩士<br>國立臺灣海洋大學<br>海洋生物研究所<br>100<br>In order to evaluate whether diatoms in the East China Sea were affected by silicon deficiency, we used the expression level of diatom silicon transporter gene (SIT) as a physiological indicator. This approach allowed us to directly detect the silicon environment sensed by a diatom cell in the East China Sea. Samples were collected on board R/V Ocean Researcher I during July 6 - 18, 2010. Works conducted included observations of diatom species composition, collection of diatom SIT sequences, and detections of SIT expression at individual stations. For SIT diversity, 48 homologous sequences were cloned. Based on phylogenetic analysis, we found that SIT sequences varied with hydrological environment, and also varied with dominant species. Many new SIT sequences were observed without an association with taxonomically described species. SIT sequences obtained in the East China Sea were used to design specific primers for Chaetoceros spp. and Skeletonema spp., and SIT expression levels were measured by real-time quantitative reverse transcription polymerase chain reaction. In order to establish a threshold expression level for silicon deficiency, a laboratory culture of Chaetoceros affinis was used in silicate-manipulation experiments. According to changes in growth rate indicated by cell numbers, the SIT mRNA expression on the 7th day was selected as the threshold value at 0.403 mol (mol EFL-1). A comparison with this threshold value revealed that all measured expression levels of Chaetoceros spp. SIT in the East China Sea were lower, which implied that Chaetoceros spp. during July 2010 cruise were not in a status of silicon deficiency. As for Skeletonema spp., spatial variation in SIT expression were consistent with the distribution of this species with reliable signals only appeared at 2 stations in the coastal zone. The significance of this expression pattern needs further clarification.

Der vorliegende Band wirft einen Blick in verschiedene Forschungsfelder, die an der Professur Interkulturelle Kommunikation der Technischen Universität Chemnitz in den letzten Jahren von Studierenden im Masterstudiengang ‚Interkulturelle Kommunikation – Interkulturelle Kompetenz‘ bearbeitet wurden. Die den sechs Artikeln zugrunde liegenden Studien nutzen Methoden der qualitativen Sozialforschung zur Datenerhebung und -auswertung. Die Artikel thematisieren interkulturelle Lernprozesse in internationalen Workcamps und interkulturellen Trainings, Erfahrungen während eines Auslandsstudiums und im interreligiösen Austausch sowie die Zusammenarbeit in multikulturellen Teams<br>This volume gives insight into different research projects conducted by students in the master‘s programme ‚Intercultural Communication – Intercultural Competence‘ at the Chair of Intercultural Communication at Chemnitz University of Technology. All empirical studies on which the articles are based use methods of qualitative social research for data collection and analysis. The articles focus on intercultural learning processes in international workcamps and intercultural trainings, experiences during studies abroad and in interreligious dialogues as well as cooperation in multicultural teams