1,720,963 research outputs found
Erratum: New technologies can support data collection on endangered shark species in the Mediterranean Sea (Marine Ecology Progress Series)
No full textReconstructing the history of the sand tiger shark (Carcharias taurus) in the Mediterranean Sea
No full textSharks are globally exposed to several anthropogenic threats, which, in many cases, have severely reduced their distribution and have impacted populations. In the Mediterranean Sea, because of its long history of exploitation and the relatively short span of scientific monitoring, reconstructing shark baselines is challenging. Many vulnerable species declined in population abundance and geographic distribution before it was possible to adequately track these changes. Consequently, for many of these species, current conservation assessments are now suffering from a severe case of shifting baseline syndrome, whereby their historical occurrence in the area is questioned.The sand tiger shark (Carcharias taurus) is one of these cases. Characterized by high philopatry, restricted home range, and low interchange between populations, its Mediterranean population may have been severely impacted by the high historical fishing pressure in the region before scientific monitoring began.In this study, the history of the abundance and distribution of C. taurus in the Mediterranean Sea was reconstructed through a comprehensive search of occurrence records in the literature and in museum collections. Between 1810 and 2008, 31 occurrence records and 54 publications provided information on the presence of the species in the area. These records were sparse but systematic over time and indicated occurrence hot spots in the south-western Mediterranean Sea and in the eastern Adriatic Sea.The presence of ten sightings of juveniles from a total of 18 sightings with length information suggested local parturition. Habitat and extinction models indicate that the area has suitable oceanographic conditions for the occurrence of the species and that the species cannot be considered extinct in the Mediterranean Sea. Our study suggests that there is still hope for the recovery of the species and underlines the crucial role of historical investigations to reconstruct the history of large elasmobranchs in the Mediterranean Sea
Dunaliella salina affects the quality of salt crystals in solar saltworks
No full textThe green alga Dunaliella salina is a common inhabitant of crystallizers of solar saltworks. Although its presence has been associated with low salt quality, little is known about the mechanism through which Dunaliella causes such effect. It has been suggested that the release of organic matter from healthy D. salina cells interferes with NaCl crystallization. With the intention to cast some light on this matter, we grew D. salina cells at different [NaCl] (0.3, 1.0, 2.0 and 3.0 M), in the presence of either NO3- or NH4+, in conditions that, although strongly hyperaline, were mild enough to minimize cell lysis and substantial spill over of cytosolic sap. The two N treatments were done because the N-source was shown to influence organic release from D. salina. We then attempted to link this physiological information to the NaCl crystals quality. In order to reduce the impact of inter-crystal inclusion and focus on the structure of the crystalline reticulum, the volume of water used for the production of crystals was as small as possible. Photosynthesis (as chlorophyll variable fluorescence associated with photosystem II), cell organic (as determined by Fourier Transform Infrared spectroscopy, FTIR) and elemental (measured by total reflection X ray fluorescence spectrometry, TXRF) composition were analyzed at the beginning and in the middle of the exponential growth phase, and in the stationary phase. The quality of the crystals obtained from sterile media and from D. salina growth media was studied by optical microscopy (to determine the shape of the crystals) and by X‐ray diffractometry.
Our results demonstrate that the presence of D. salina cells is directly connected to alterations of NaCl crystalline structure (specifically of crystallite size) and with the quantity and quality of contaminants
Historical DNA as a tool to genetically characterize the Mediterranean sand tiger shark (Carcharias taurus, Lamniformes: Odontaspididae): A species probably disappeared from this basin
Full text linkThe sand tiger shark (Carcharias taurus) is a coastal species distributed in temperate and sub-tropical waters, classified as ‘Vulnerable’ at global level and ‘Critically endangered’ in eastern Australia, south-western Atlantic Ocean, and Mediterranean Sea. Six populations (north-western Atlantic, Brazil, South Africa, Japan, eastern Australia, and western Australia) with low genetic diversity and limited gene flow were identified worldwide, but genetic information for many other geographic areas are still missing. Specifically, this species is listed in several reports as part of the Mediterranean fauna, even if there has been a lack of catches and sightings in recent years in this basin. To clarify the origin of C. taurus individuals caught in the past in the Mediterranean Sea, historical samples were genetically analysed. Nine samples with certain Mediterranean origin were collected from different European museums. DNA was extracted and ~600 bp of the mitochondrial DNA control region were amplified using eight overlapping species-specific primer pairs. Sequences obtained were aligned with all the haplotypes globally known so far. Genetic analysis revealed the misidentification of one museum specimen. Among the remaining Mediterranean historical samples, three different haplotypes were recovered. Two of them previously observed only in South Africa and one described in both South African and Brazilian populations. Results suggest a genetic relationship between Mediterranean sand tiger sharks and those from the western Indian Ocean. According to previous studies, we hypothesized that, during the Pleistocene, the cold Benguela upwelling barrier was temporarily reduced allowing the passage of C. taurus individuals from the Indian to Atlantic Ocean. After the restoration of this phylogeographic barrier some individuals were trapped in the Atlantic Ocean and probably migrated northward colonizing the western African coasts and the Mediterranean 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
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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