1,720,976 research outputs found
An experimental protocol to select nematode species from an entire community using progressive sedimentary enrichment.
No full textThe purpose of this study was to introduce free-living marine nematodes to the ‘world of biomarkers’.Biomarkers are still not used in the monitoring and assessment of this highly diverse phylum, becausethe technique needs to be applied at the single species level. This incurs high costs and involves time-consuming procedures, which are currently the main pitfalls when it comes to the application of thesetechniques to marine nematodes. Consequently, this work proposes an innovative protocol for selectinga single species from an entire community of nematodes using two independent selection processeswhereby the sediment of the microcosms is progressively and separately enriched with fine and coarsesediment fractions. During our experiment, the abundance and number of nematode species decreaseddiscernibly with exposure to both finer and coarser sediment. Multivariate analyses revealed that deposit-and epigrowth-feeders were the most tolerant feeding guilds, probably due to their deposit-feedingand microvore behaviours. At the end of the experiment, Terschellingia longicaudata and Ptycholaimellusponticus became the unique members of the community when the sediment was enriched with fine andcoarse sediment particles, respectively. After the complete alteration of the community, and when themono-species level had been achieved, it was possible to maintain these two species alive, and withoutany drop in numbers, under the same laboratory conditions considered during the selection process.Accordingly, the protocol adopted here lays new foundations for the study of nematodes in the biomarkerfield
Environmental quality assessment of El Bibane lagoon (Tunisia) using taxonomic and functional diversity of meiofauna and nematodes
No full textThe lagoon of El Bibane (Tunisia) is a Mediterranean coastal area that is affected by an increasing human impact. Thus, an
estimation of its biodiversity and an ecological quality assessment are very urgent. This study investigates the meiofaunal and
nematode communities of the El Bibane lagoon both from a taxonomic and a functional point of view. Nematodes were the
dominant group as is common in brackish water systems. The nematode community was made up of 62 genera in 22 families.
Xyalidae, Chromadoridae and Cyatholaimidae were the richest and most abundant families. The taxonomic composition
and biodiversity of nematodes were comparable to those found in other European and Mediterranean transitional areas.
Both meiofauna and nematodes showed a clear subdivision between marginal and central areas. The central stations, represented
by fine sediments and higher amounts of organic carbon, seemed to be characterized by low meiofaunal densities,
nematode diversity and a strong dominance of 1B and 2B trophic guilds. These trends could be related not only to the
grain size and organic load, but also to a possible influence of tidal currents that can transport pollutants in the central
area of the lagoon coming from the adjacent coastal areas. Shannon diversity and life strategies are not always in agreement
in defining the ecological quality, but an overall worse ecological quality was detected especially at S6. The results of this study
are an important starting point for the future monitoring of the potential and actual human impact on the El Bibane area
over time
Impact of the biocide Irgarol on meiofauna and prokaryotes from the sediments of the Bizerte lagoon—an experimental study
No full textEffects of antifouling booster biocide Irgarol 1051 on the structure of free living nematodes: a laboratory experiment
No full textA mesocosm experiment was conducted to evaluate the effects of Irgarol on nematode diversity, composition and trophic structure. Sediment samples were experimentally contaminated using four increasing Irgarol concentrations [I1 (11.5 ng g-1), I2 (35 ng g-1), I3 (105 ng g-1) and I4 (315 ng g-1)] and compared to non-contaminated sediments (controls). Nematode diversity as the number of nematodes species (S) and species richness (d) was significantly lower in all Irgarol treatments than in the controls while the evenness (J′) increased significantly in I4 treated mesocosms. The nematode species composition significantly changed following Irgarol concentrations. Paracomesoma dubiun and Terschellingia longicaudata appeared as "tolerant" species to the highest Irgarol concentration. Additionally, Chromadorina germanica and Microlaimus cyatholaimoides appeared as "opportunistic" species. In contrast, Daptonema normandicum seemed to be a "sensitive" species to Irgarol contamination. Irgarol modified also the nematode trophic structure where the relative abundance of deposit feeders decreased significantly in all the treatments compared to control mesocosms and optional predators decreased only in treated mesocosms with I3. Epigrowth feeders increased significantly in treated mesocosms with I3 and I4 and the microvores increased with I1 and decreased with I4. The relative abundance of ciliate consumers appeared unaffected by the presence of Irgarol contamination. Our results open new perspectives on the potential impact of antifouling booster biocide Irgarol 1051 on nematode biodiversity and functional diversity as trophic structures
Spatio-temporal evolution of the community structure free-living nematodes in response to the petroleum pollution in the Bizerte Bay
No full textThe spatio-temporal evolution of the community composition of nematodes exposed to petroleum pollution in the Bay of Bizerte, Tunisia, was studied in 7 sampling stations. 101 species of free-living marine nematodes, belonging to 28 families were found, from all of the stations put together, in summer 1992 compared with 54 species belonging to 22 families in summer 1996. Sediment enrichment with hydrocarbons is responsible for the temporal restructuring of the nematode communities. The spatio-temporal heterogeneity of the qualitative data, in terms of diversity, composition or functional maturity is confirmed by sediment analysis. Two sources of petroleum pollution are found, the discharge of refinery and the tankers berthing at proximity, but their importance is temporally variable.Publishe
Toxicity of pesticides and polycyclic aromatic hydrocarbons on marine bivalves : impacts of exposure to metallic nanoparticles
No full textL’objectif de cette thèse est d’étudier les effets de l’exposition individuelle ou en combinaison de certaines nanoparticules (NPs), de certains hydrocarbures polycycliques et pesticide sur les bivalves par le biais d’une approche multi-marqueurs (chimique, physiologique et biochimique). Pour atteindre cet objectif, le modèle biologique choisis est la moule Mytilus galloprovincialis. La réponse physiologique corresponde à l’évaluation de la capacité de filtration et de respiration de la moule et la réponse biochimique est étudiée à travers quelques biomarqueurs tels que la superoxyde dismutase (SOD), la catalase (CAT), le malondialdéhyde (MDA) et l'acétylcholinestérase (AChE). Les principaux résultats des analyses chimiques en utilisant la microscopie électronique à transmission (MET), la diffraction des rayons X, la diffusion dynamique de la lumière et le potentiel zêta confirment la taille nanométrique des NPs considérées et révèlent leurs stabilités aux changements des paramètres environnementaux (pH et salinité). L’estimation de la toxicité des NPs, des HAPs et des pesticides au moyen des paramètres physiologiques ont montré que l’effet dépend du produit chimique considéré et de la concentration. De plus, les paramètres de stress oxydants et de neurotoxicité ont montré que l’impact dépend du contaminant, de la concentration et de l’organe mis en jeu. Au vu d’ensemble, l’utilisation d’une approche intégrative associant des analyses chimiques et écotoxicologiques représente un bon moyen pour comprendre le profil relationnel entre les contaminants et les organismes aquatiques qui s’écoule dans le cadre de programmes de biosurveillance des écosystèmes côtiers.The main goal of this thesis is to study the effects of exposure individually or in combination to certain nanoparticles (NPs), certain polycyclic aromatic hydrocarbons and pesticides on bivalves through a multi-marker approach. To achieve this objective, the biological model chosen is the mussel Mytilus galloprovincialis. In addition, the impact of co-exposure to binary mixtures (NPs-PAHs and NPs-pesticides) on the physiological and biochemical response was assessed. The physiological response corresponds to the evaluation of the filtration and respiration capacity of the mussel and the biochemical response is studied through a few biomarkers such as superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA) and acetylcholinesterase (AChE). In parallel, PAHs photodegradation using NPs forms was studied showing different profiles related to each contaminant.The main results of NPs chemical analyzes using transmission electron microscopy (TEM), X-ray diffraction, dynamic light scattering and zeta potential confirm the nanometric size of the considered NPs and reveal their stability to environmental parameters changes ( pH and salinity). The estimation of the toxicity of NPs, PAHs and pesticides using physiological parameters showed that the effect depends on the chemical proprieties of each considered compound and on the concentration. In addition, oxidative stress and neurotoxicity parameters have shown that the impact depends on the contaminant, the concentration and the organ involved.Overall, the use of an integrative approach combining chemical and ecotoxicological analyzes represents a good way to understand the relational profile between contaminants and aquatic organisms flowing the framework of coastal ecosystem biomonitoring programs
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
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