1,721,003 research outputs found
Flash Flood simulation and valve behavior of Mytilus galloprovincialis measured with Hall sensors
Get PDFMussels close their shell as a protective strategy and the quantification of this behavioral marker may represent an alarm signal when they are exposed to environmental stressors. In the present study, we investigated the ability of the Mediterranean mussel Mytilus galloprovincialis to recover and then the resilience or inertia of valve activity after a pulsing exposition to diverse levels of salinity (5, 10, 20 and 35 PSU as reference value). The trial simulated an event of drastic and sudden reduction of seawater salinity thus mimicking an event of Flash Flood from intense rain. Valve gaping and movements were measured in continuous cycle for ten days using a customized magneto-electric device which uses Hall sensors. Results showed that under normal conditions of salinity (35 PSU) the general pattern of valve movements was a continuously open state with sporadic spikes indicating a closing motion. At salinity of 5 PSU mussels reacted by closing their valves, leading to a 77% mortality on the fourth day. At salinity of 10 PSU animals were observed with closed valves for the entire duration of the exposure and no mortality occurred, they showed a significant reduction in the valve activity once the reference value of salinity was re-established. In contrast, salinity of 20 PSU did not trigger a significant behavioral response. Interestingly, there no define rhythms of valve movements were recorded during salinity challenges
Blue-Green Algae as Stimulating and Attractive Feeding Substrates for a Mediterranean Commercial Sea Urchin Species, Paracentrotus lividus
Get PDFSea urchins rely on chemical senses to localize suitable food resources, therefore representing model species for chemosensory studies. In the present study, we investigated the chemical sensitivity of the Mediterranean sea urchin Paracentrotus lividus to the blue-green alga Aphanizomenon flos-aquae, namely "Klamath", and to a few amino acids chosen from the biochemical composition of the same algae. To this end, we used the "urchinogram" method, which estimates the movement rate of the sea urchins in response to chemicals. Our results showed that Klamath represents a strong chemical stimulus for P. lividus as it elicits an overall movement of spines, pedicellariae, and tube feet coupled, in some cases, to a coordinated locomotion of the animals. Sea urchins also displayed a sensitivity, even if to a lesser extent, to leucine, threonine, arginine, and proline, thus implying that the amino acids contained in Klamath may account, at least in part, for the stimulating effects exerted by the whole algae. Additionally, our results show that Klamath, as well as spirulina, another blue-green alga with high nutritional value, is very attractive for this sea urchin species. These findings gain further importance considering the potential profit of echinoderms for commercial consumers and their growing role in aquaculture. Klamath and spirulina combine high nutritional profiles with attractive and stimulating abilities and may be considered potential valuable feed supplements in sea urchin aquaculture
The effect of Mistral (a strong NW wind) episodes on the occurrence and abundance of Atlantic bluefin tuna (Thunnus thynnus) in the trap fishery of Sardinia (W Mediterranean)
Get PDFFrom April to June Atlantic bluefin tuna, Thunnus thynnus, migrate along the western Sardinian coastline in a southward direction, where they are intercepted by the trap fishery. Fishermen claim that Mistral episodes facilitate the entry of tuna schools towards the traps, thus increasing capture rates. To test the fishermen’s hypothesis we conducted underwater visual counts of tuna in the trap chambers and analysed these data under the effect of wind. The results indicate a “stair-step” pattern in the abundance of tuna, demonstrating that major increases in abundance are associated with the Mistral. The second analytical approach involved a longer time scale to test whether higher Mistral occurrences corresponded to periods when higher captures were recorded. Using a linear regression model we found a significant correlation (p15 knots seemed to have a negative effect on captures. This pattern may be caused by wind-induced advection of coastal waters generating a physical boundary that may have had a deterrent effect on tuna schools
Microbiological characterization of a rearing system for the common sea urchin Paracentrotus lividus: a support to technical production regulations redaction and system monitoring
Get PDFObjective: The overexploitation of the sea urchin Paracentrotus lividus stock, as a consequence of the growing market demand for roe, has boosted the research for echinoderm rearing. The chemical, physical, and microbiological characteristics of land-based facilities are crucial for sea urchins' health and human consumption of their products. In Italy, health-hygienic regulations for P. lividus rearing are still to be perfected by the authorities. In this context, we characterized the microbiological quality of a pilot land-based facility for sea urchin production at the University of Cagliari (Italy) to support the development of technical production regulations.Materials and Methods The accredited Hygiene Laboratory of Cagliari University collected and analyzed the samples in June 2023. Mesophilic bacteria, yeasts, and molds were searched for in air and on surfaces. Total coliforms and Escherichia coli, Enterococci, Pseudomonadaceae, Staphylococcus aureus, sulfite-reducing Clostridia, and Vibrio spp. were identified in water samples. We searched forVibrio spp. and Pseudomonas spp. in the gonads and coelomic fluid of sea urchins.Results Although air, surfaces, and water quality were satisfactory overall, some critical points should be monitored more strictly. Enterococci concentration was 250 CFU/100 mL in the water reserve, suggesting animal contamination (other than humans). Pseudomonas aeruginosa was the most resistant to filtration processes, with a residual concentration of 6 CFU/250 mL after the second filtration. No colonies of Vibrio spp. or Pseudomonas spp. were isolated in sea urchins' gonads or coelomic fluid.Conclusions Starting from the results, we provided targeted advice for developing technical production regulations, system monitoring, and facility routine maintenance in accordance with the 'best practice' approach. This analysis could be considered a first step toward the elaboration of common regulations about the minimal standards for the breeding environment of P. lividus by national and regional authorities
Spatial distribution patterns and population structure of the sea urchin Paracentrotus lividus (Echinodermata: Echinoidea), in the coastal fishery of western Sardinia: a geostatistical analysis.
Get PDFThe identification of appropriate spatial distribution patterns for the observation, analysis and management of stocks with a persistent spatial structure, such as sea urchins, is a key issue in fish ecology and fisheries research. This paper describes the development and application of a geostatistical approach for determining the spatial distribution and resilience of the sea urchin Paracentrotus lividus population in a fishing ground of western Sardinia (Western Mediterranean). A framework, combining field data collection, experimental modelling and mapping, was used to identify the best-fit semivariogram, taking pre-fishing and the post-fishing times into consideration. Variographic analyses indicate autocorrelation of density at small distances, while the isotropic Gaussian and spherical models are suitable for describing the spatial structure of sea urchin populations. The point kriging technique highlights a generally patchy population distribution that tends to disappear during the fishing season. Kriging maps are also useful for calculating predictable stock abundances, and thus mortality rates, by class diameters within six months of fishing. We conclude that the framework proposed is adequate for biomass estimation and assessment of sea urchin resource. This can therefore be regarded as a useful tool to encourage a science-based management of this fisher
Sperm number and structure of the black-striped pipefish Syngnathus abaster (Teleostei, Syngnathidae)
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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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