1,721,014 research outputs found
Grazing experiments with Oxyrrhis marina and coccolithophores
No full textIn laboratory culture experiments, calcified and decalcified coccolithophore cells were offered as prey to a phagotrophic predator, both in separate pure cultures with calcified or decalcified cells only, and in mixed cultures that contained both cell types. Overall, three experiments were conducted, each with a different coccolithophore species. The prey and predator concentrations were monitored over the course of each experiment by flow cytometry and microscopic counting
Growth of scyphozoan polyps under different feeding conditions
No full textScyphozoa play an important role in marine ecosystems. In recent years, rising numbers of jellyfish have been observed worldwide, with potentially dramatic effects for the food web. Jellyfish have a complex life cycle which includes a changing of generations. The medusae stages are much larger and more visible and have therefore been more intensely studied than the polyp generation, which is smaller, benthic and sessile. Polyps, however, are a crucial life stage in the recruitment of Scyphomedusae and therefore require more investigations in order to assess their importance in marine ecosystems. This study contributes to the understanding of the ecology and food spectrum of the polyps. To date very little is known about the feeding of polyps, in particular with regard to the food size. As food is a determining factor in the survival and development of polyps, this study investigates the size class of food best suited for two different polyp sizes. The polyps were fed with Artemia of four different and distinct size classes and their growth determined with different measurements. The results of this study indicate that larger polyps are capable of feeding on a wider range of prey sizes than the small polyps. Prey organisms of an optimal size have to be smaller than the polyp feeding on it in order to enable direct and complete ingestion of the prey item
Growth response of Emiliania huxleyi to ocean alkalinity enhancement
No full textWe tested the sensitivity of Emiliania huxleyi, the most widespread coccolithophore species, to ocean alkalinity enhancement in laboratory culture experiments. The manipulation involved adding a NaOH (1 M) solution.
The experiment was conducted at the GEOMAR Helmholtz Centre for Ocean Research Kiel. Cells were acclimated for seven to nine generations to the respective experiment conditions. Cell density was recorded throughout the experiment with BD Accuri C6 Flow Cytometer. Samples for total particulate carbon (TPC) and particulate organic carbon (POC) were measured in an elemental analyzer (Euro EA, EuroVector). TA concentrations were determined by potentiometric titration with a Metrohm Compact 862 Titrosampler and corrected with certified reference material (A. Dickson, Scripps Institution of Oceanography, La Jolla, California). DIC concentrations were measured with an Automated Infrared Inorganic Carbon Analyzer (AIRICA) equipped with a LI-COR detector (LI-7000 CO2/H2O analyzer
No observed effect of ocean acidification on nitrogen biogeochemistry in a summer Baltic Sea plankton community
No full textNitrogen fixation by filamentous cyanobacteria supplies significant amounts of new nitrogen (N) to the Baltic Sea. This balances N loss processes such as denitrification and anammox, and forms an important N source supporting primary and secondary production in N-limited post-spring bloom plankton communities. Laboratory studies suggest that filamentous diazotrophic cyanobacteria growth and N2-fixation rates are sensitive to ocean acidification, with potential implications for new N supply to the Baltic Sea. In this study, our aim was to assess the effect of ocean acidification on diazotroph growth and activity as well as the contribution of diazotrophically fixed N to N supply in a natural plankton assemblage. We enclosed a natural plankton community in a summer season in the Baltic Sea near the entrance to the Gulf of Finland in six large-scale mesocosms (volume ??55?m3) and manipulated fCO2 over a range relevant for projected ocean acidification by the end of this century (average treatment fCO2: 365–1231?µatm). The direct response of diazotroph growth and activity was followed in the mesocosms over a 47 day study period during N-limited growth in the summer plankton community. Diazotrophic filamentous cyanobacteria abundance throughout the study period and N2-fixation rates (determined only until day 21 due to subsequent use of contaminated commercial 15N-N2 gas stocks) remained low. Thus estimated new N inputs from diazotrophy were too low to relieve N limitation and stimulate a summer phytoplankton bloom. Instead, regeneration of organic N sources likely sustained growth in the plankton community. We could not detect significant CO2-related differences in neither inorganic nor organic N pool sizes, or particulate matter N?:?P stoichiometry. Additionally, no significant effect of elevated CO2 on diazotroph activity was observed. Therefore, ocean acidification had no observable impact on N cycling or biogeochemistry in this N-limited, post-spring bloom plankton assemblage in the Baltic Sea
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Why do coccolithophores calcify? Does the calcium carbonate shell serve as protection against viral infection and predation?
Full text linkCoccolithophores are an important group of marine phytoplankton that are characterized by their ability to precipitate calcium carbonate. The single cells form small calcite plates (coccoliths), which are arranged on the cell surface in form of a spherical coating, called coccosphere. Coccolithophores account for a significant proportion of the marine primary production and are among the most important calcifying organisms in the ocean, thus having a significant impact on the marine carbon cycle. However, it is not known in what way their ability to calcify contributes to their ecological success, as the question of why coccolithophores calcify remains unanswered. Probably the most obvious theory is that the coccosphere provides protection against natural predators, the most relevant of which are viruses, microzooplankton (unicellular protists), and mesozooplankton (metazoan predators). By means of laboratory experiments, this work investigated whether the coccosphere of certain species provides protection against infection with a virus, a phagotrophic protozoan, and a copepod. The results show that the coccosphere does not prevent infection with the specific virus and reveal complex infection dynamics in the investigated host-virus system. It is further shown that the coccosphere does not protect against grazing by a certain copepod species. Experiments with a phagotrophic protozoan showed that the coccosphere affects food uptake and growth of the predator, but does not cause the grazer to avoid ingesting coccolithophores and to select non-calcified cells that were offered at the same time. The results raise the questions whether other microzooplankton predators that naturally co-occur with coccolithophores are able to select against calcifying cells, and whether the effect of calcification on the growth of nonselective protozoa provides a benefit for coccolithophores
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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