1,720,973 research outputs found
Use of the dilution technique to determine microzooplankton herbivory in three contrasting oceanic systems
No full textThe dilution technique has been used during both laboratory experiments and in the field in three contrasting oceanic systems: the northeast Atlantic, Bellingshausen Sea and Arabian Sea. Laboratory dilution grazing studies, using Oxyrrhis marina as the predator and Dunaliella tertiolecta as prey, have demonstrated a significant linear relationship between apparent phytoplankton growth and dilution factor. The daily turnover of prey by Oxyrrhis ranged between 45 and 95%. Growth of prey was constant at all dilutions demonstrating that phytoplankton growth was density independent. Studies carried out during summer along a transect in the northeast Atlantic between 60°N and 47°N showed microzooplankton to consume between 0.5 and 17mg phytoplankton C d"\ This was equivalent to between 288 and 589 mg C m ^ d"^ being grazed in the mixed layer. Microzooplankton grazing impact was highest at the southerly end of the transect. During the spring-bloom period in 1990, microzooplankton grazed between 28 and 78% and between 26 and 55% of the daily primary respectively. The microzooplankton community was dominated by small cells (<20|jm). In the Bellingshausen Sea, microzooplankton consumed between 0.04 and 31.21 mg C m ^ d'\ and were estimated to graze between 21 and 3260 mg C m ^ d'^ in the pack ice and open water station respectively. In the Arabian Sea, microzooplankton grazed between 1 and 17 mg C m"^ d'\ In the mixed layer microzooplankton grazed between 161 and 415 mg C m"^ d"^ during the SW monsoon and between 110 and 407 mg C m"^ d"^ during the intermonsoon period. Substantial grazing of phytoplankton biomass by the microzooplankton occurred in all three oceanic systems. Variations in the grazing and phytoplankton growth rates can be attributed to differences in the phytoplankton and microzooplankton communities encountered. Results demonstrate a tight coupling between growth of prey and consumption for the northeast Atlantic and Bellingshausen Sea. production in May and June</p
The herbivorous impact of microzooplankton during two short-term Lagrangian experiments off the NW coast of Galicia in summer 1998
No full textMicrozooplankton (heterotrophic microplankton and heterotrophic nanoflagellates) and their herbivorous activity were estimated from dilution experiments in August 1998 during two Lagrangian drift experiments that sampled contrasting conditions—an upwelling/relaxation event along the shelf edge and an oligotrophic offshore filament. During upwelling/relaxation, heterotrophic microplankton were present at mean surface concentrations between 15,000 and 48,000 cells l?1. Heterotrophic nanoflagellate concentrations were between 200 and 700 cells ml?1 and the most abundant component of the heterotrophic microplankton was the aloricate choreotrich ciliates which increased dramatically in concentration from 6,000 to 24,000 cells l?1 during the first 4 days of the study. Total microzooplankton biomass reached a maximum of 39mgC.m?3. In the filament, which developed from the upwelling, cell concentrations were lower and averaged 4,500 cells l?1 for heterotrophic microplankton and 250 cells ml?1 for heterotrophic nanoflagellates. Total microzooplankton biomass was about 10–12mgC.m?3. Microzooplankton turned over between 40 and 85% of the phytoplankton standing stock, thereby consuming between 5 and 78mg phytoplankton carbon.m?3.d?1. The magnitude of this activity was highest during upwelling/relaxation and was positively correlated to heterotrophic nanoflagellate biomass and chlorophyll-a concentration but not heterotrophic microplankton biomass. The proportion of primary production grazed decreased from 160 to 59% d?1 during upwelling/relaxation and ranged between 60 and 90% d?1 in the filament. Microzooplankton herbivory within the euphotic zone increased from 684 to >2000mgC.m?2.d?1 during upwelling/relaxation and was between 327 and 802mgC.m?2.d?1 in the filament. Although microzooplankton herbivory was lower and less variable during the filament study, microzooplankton consumed on average 60% of the phytoplankton standing stocks which was higher than found during upwelling/relaxation. Microzooplankton assimilation efficiency ranged between 3 and 33% during upwelling/relaxation and between 0 and 13% in the filament. Our data demonstrate a close coupling between phytoplankton growth and microzooplankton herbivory in surface waters off the Galician Coast and suggest that microzooplankton may have been a significant sink for phytogenic carbon during August 1998
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
Seasonal variation of zooplankton community structure and trophic position in the Celtic Sea: a stable isotope and biovolume spectrum approach
No full textZooplankton on continental shelves represent an important intermediary in the transfer of energy and matter from phytoplankton to the wider ecosystem. Their taxonomic composition and trophic interactions with phytoplankton vary in space and time, and interpreting the implications of this constantly evolving landscape remains a major challenge. Here we combine plankton taxonomic data with the analysis of biovolume spectra and stable isotopes to provide insights into the trophic interactions that occur in a shelf sea ecosystem (Celtic Sea) across the spring-summer-autumn transition. Biovolume spectra captured the seasonal development of the zooplankton community well, both in terms of total biomass and trophic positioning, and matched trophic positions estimated by stable isotope analysis. In early April, large microplankton (63-200 µm) occupied higher trophic positions than mesozooplankton (>200 µm), likely reflecting the predominance of nanoplankton (2-20 µm) that were not readily available to mesozooplankton grazers. Biomass and number of trophic levels increased during the spring bloom as elevated primary production allowed for a higher abundance of predatory species. During July, the plankton assemblage occupied relatively high trophic positions, indicating important links to the microbial loop and the recycling of organic matter. The strong correlation between biomass and community trophic level across the study suggests that the Celtic Sea is a relatively enclosed and predominantly energy-limited ecosystem. The progression of the zooplankton biomass and community structure within the central shelf region was different to that at the shelf-break, potentially reflecting increased predatory control of copepods by macrozooplankton and pelagic fishes at the shelf break. We suggest that the combination of size spectra and stable isotope techniques are highly complementary and useful for interpreting the seasonal progression of trophic interactions in the plankton
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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